James Webb is fully deployed | Hacker News Reader

James Webb is fully deployed

nasa.gov

1,384 pointsSami_Lehtinen494 comments

More great news. Congratulations to all who have worked on the project.

I understand the reasons for not putting a camera on or near the JWST, but I’m still a little sad that we’ll probably never get to see the thing in situ in all its operational glory.

Maybe one day when it finally expires, we can launch a “sample return” mission to tow it back.

RE>> "I understand the reasons for not putting a camera on or near the JWST"

What are the reasons? I'm sorry ~ I'm ignorant on the topic, but I'd love to learn more. Why/what are the reasons?

Great blog post from NASA themselves explaining it: https://blogs.nasa.gov/webb/2022/01/06/why-doesnt-webb-have-...

the post is really not very long and I would suggest getting it straight from the horse's mouth, but for those not willing to devote a click here are arguably the most relevant bits!

"deployment surveillance cameras would not add significant information of value for engineering teams commanding the spacecraft from the ground."

"Webb’s built-in sense of ‘touch’ (for example, switches and various mechanical, electrical, and temperature sensors) provides much more useful information than mere surveillance cameras can," said Geithner. "We instrumented Webb like we do many other one-of-a-kind spacecraft, to provide all the specific information necessary to inform engineers on Earth about the observatory’s health and status during all activities."

Perhaps one day they could send a robot mechanic along with the mission, and then a camera could be of value.

I’m sure if we ever have sufficient technology to build a city on the moon, the first museum exhibit will be a captured JWST

No. The museum will be built atop its first exibit: tranquility base. See Futurama s01e02.

For the sake of correctness, Tranquility Base is not where the museum is built upon in Futurama S01E02; you must be misremembering. In fact, the moon landing site is considered lost at the beginning of that episode.

When it's later found in the episode, it's found with the lunar ascent module still attached. Because the astronauts ascended in this module, only the descent modules should be there, so you might at first think that this is a blatant mistake on the part of the writing staff and you might hope someone was fired for that blunder[1]. However, if you pay close attention, there's a plaque behind Leela while she's in the ascent module that states "Lander returned to this site by the Historical Stickler's Society."[2]

[1]: https://www.youtube.com/watch?v=FTxw5nQX7SA [2]: https://www.reddit.com/r/futurama/comments/91kssj/i_didnt_wa...

My bad. I do remember the issue re the assent module, and the sign, but forgot that they escaped into the lander after leaving the dome.

The book Artemis proposes this also.

One thing they mentioned that kinda sends it home to me is that the telescope is aimed at the dark and away from the sun, and the other side is especially reflective[0]. In other words, one side is too dark to see, and the other is too bright to see.

[0]:https://twitter.com/NASAWebb/status/1479161991252131841

Couldn't they just use an image intensifier tube for night vision? I think they should just stick with the excuse of it being costly and unnecessary.

We're talking about "see the faintest light from stars millions of lightyears away"-dark (for that reason you also can't shine a light on it), with our sun in the background. To see something on that side, you'd basically need the vision capabilities the telescope itself has and that's obviously not going to happen.

It obviously needs a selfie mirror.

It has a selfie 'lens': NIRcam has extra optics that can be swung in that allows the camera to focus on the primary mirror instead of out in the great infinity.

So in this sense webb is already a camera which can photograph itself!

This capability exists for mirror alignment: They'll point webb at an isolated star, switch to focusing on the primary mirror, swap in optics that cause small phase differences to result in diffraction patterns, and then they can use the resulting images to fine tune the positioning of the mirror segments to a small fraction of the wavelength of light that they're using.

That's amazing. I was wondering how they did that. Every new thing I learn about this machine blows me away.

> to see something on that side, you'd basically need the vision capabilities the telescope itself

I'm not sure if that's correct - there's a lot of photons hitting the telescope (the night sky), and night vision systems can work off of a relatively small number of photons

> the telescope is aimed at the dark and away from the sun

To be more specific; It's "parked" in an orbit [0] that constantly puts Earth between the sun and James Webb.

So it's not only aimed away from the sun, Earth is also acting as a planetary scale sunscreen for it.

[0] https://en.wikipedia.org/wiki/Lagrange_point

Actually JWST orbits around L2 at appreciable altitude. The unique aspect of the orbit is that it is never in the shadow of the Earth or moon. It guarantees consistent solar power and thermal load.

https://jwst-docs.stsci.edu/jwst-observatory-characteristics...

Wow. I’m an astronomer and somehow I never learned this! Thank you for the link!

Of course a solar powered satellite can’t be parked in the shade. Can’t believe I never thought about that.

It can, it has batteries, but you don’t want to mess with thermals on that thing.

My first thought is, "Why didn't they eschew solar power entirely and 'simply' park it in the shade?"

Surely they considered that, and the wins would have been massive -- no sunshields needed. So I'm sure the downsides must have been massive as well. Not enough plutonium fuel, or perhaps it just wouldn't provide enough power over the life of the mission. And of course the radioactive fuel would generate its own heat as well.

Now I need to find out more about that decision....

edit: Another commenter mentioned, "The earth's shadow never reaches L2 anyhow - it's only penumbra at that distance since the angular size of the earth is smaller then the angular size of the Sun." If that's correct, then there was never truly an option of "parking it in the shade" anyway.

The dark side of the Earth is very bright in IR. Getting far away from the Earth and moon makes them dimmer. Also, going for L2 makes sure the Earth, moon, and Sun are all always in the same direction, so the sun shield will block all significant IR sources.

That explains the animation! I just thought NASA was just adding some more realism into the orbit animation by adding what looked like a wobble. Derp.

One of the fascinating bits is how much engineering has gone into keeping the detectors cold. Because JWST is (primarily?) taking images in the mid-IR region, it is crucially important to keep the detectors cool otherwise you'd just be swamped in background noise. Keeping things cold in space is despite it being a cold place actually extremely difficult, because you can't use convective cooling. If something sits in the sun "all-day" it gets warm, so the whole reason for the sunshield is to keep the instruments cool. On top of that they are using active cooling for the (IIRC) first time on a satellite. I saw a presentation from one of the engineers two years ago and it's absolutely fascinating stuff.

Given that this does not really give the orbit any real significance in terms of being shaded by the Earth from the Sun, is there another reason it's there?

I guess it gives you a very stable position for observations, but why not just put it in solar orbit then? Then again this is kind of a solar orbit that happens to stay close to the Earth at all times so that's a plus for comms.

That's exactly what L2 is. Otherwise the orbits of JWST and Earth would have different periods. It's handy to be able to have constant high speed communications and not need large antennas with blackouts.

It also is handy to keep the closest IR sources (Earth and moon) in the same direction as the sun at all times so there is never a point where you have a significant IR source above the sun shield.

Ah yes I hadn't considered the IR sources aspect, that makes a lot of sense.

It’s orbiting around L2. I’m not sure if it’s actually in the shadow of earth. Keep in mind that it’s still powered by a solar array.

JW does indeed circle that Lagrange point, but it is definitely not in Earth’s shadow.

The JW orbit semi major axis (about the L2 point) is order of 500,000 km. The radius of Earth is about 6500 km. Thus, the shadow of the Earth is extremely small compared with the excursions of JW.

The earth's shadow never reaches L2 anyhow - it's only penumbra at that distance since the angular size of the earth is smaller then the angular size of the Sun

Good point. JW is at about 1.01 AU, and the solar radius is a bit over 100x the Earth radius, so there’s not really even a “shadow”.

Besides the sun being so stupendously large that the L2 point isn't in the direct shade cone anymore. At the orbit it is in full sunshine as though the Earth isn't there.

It seems to me that that isn't quite right. "Dark" just means no visible light, but an infrared or thermal camera could see stuff. The article above mentions this possibility and the problems, which are harnessing and operating at cryogenic temperatures.

The point of the telescope is to capture IR light from space, if the telescope itself were generating IR light itself it would disrupt the sensor and data that it collects. Part of why its going to take so long for it to begin operating is that it needs to cool down to ultra cold temperatures before beginning operation.

Who said anything about generating infrared light? And I don't know what your last sentence is in reference to. Yes, it needs to cool down. Why is that relevant to this discussion other than what's already mentioned about that being a downside to operating cameras?

From the article so people can just debate NASA's own reporting:

> Although infrared or thermal-imaging cameras on the cold side could obviate the need for illumination, they would still present the same harnessing disadvantages. Furthermore, cameras on the cold side would have to work at very cold cryogenic temperatures.

The JWST has an extremely sensitive IR camera. And it is going to cool down to near absolute zero so that the IR sensors don't get flooded with radiation from the rest of the telescope. Because it will get so cold, it is not going to be emitting much IR (I think this is what the GP said when they said "generating"). Your typical deployment observation IR camera's won't be of much help in that case.

That makes sense, and I got thrown off (by maybe misreading the comment) thinking they meant the camera or something else would generate additional IR to illuminate the telescope, which I got confused by. It makes sense now that the comment was meaning that the cool down was to reduce as much telescope generated IR noise as possible.

I think that article is leaving out some of the other problems (which is understandable, it already covers plenty of downsides). The whole point of keeping the cold side cold is so that it doesn't emit any IR radiation (otherwise the JWST couldn't work). So by design it's "dark" to an IR or thermal camera in the same way it's dark to a visible light camera. Certainly you can build a camera to see it anyway (without extra lights), but the question then becomes how big that camera has to be, and I would assume it's way to big to be realistic.

That makes sense. Thanks. It was a question of mine just how much IR would be there to see.

First it’s possible to send up a camera that would be sensitive enough to use starlight to capture images on the dark side. However, those things aren’t light and would come at the cost of less propellant for minimal gain. Adding a tiny camera and a tiny light at the same time would also be possible but there really isn’t anything worth looking at via a single camera.

As to using infra red camera, they simply don’t work on objects the same temperature as the camera. NASA could have sent one up with a cooling system to look at the cold side of the sunshade, but again weight and pointlessness means it’s just wasteful.

It's probably not practical for JWST, but starlight is actually fairly bright. If you travel to somewhere with essentially zero light pollution, like a desert, if it's a clear sky you can see with starlight. At the South Pole on a clear night we would walk out to the dark sector (where the telescopes are) with our headlamps off because it just wasn't necessary. The only illumination sources outside were red safety lights[1] and we'd normally turn those off for long exposure photography. You do need a fast lens though, and that inevitably means lots of glass.

Whether the telescope is reflective enough to get a good photo is another matter - I would guess not, it's designed to minimise stray light.

As for IR, the telescope is probably bright compared to the background at least for now. The main issue though is whether you'd need to actively cool the engineering camera. Cooling stuff in space is difficult because you can only really dump heat via radiation. It's probably not worth the weight to carry a separate cryocooler just for that. The inability to conduct heat is partly why it takes so long to cool down, aside from minimising thermal stress on the infrastructure.

[1] The main reason they exist is so that you have a point of reference when walking about outside, particularly on foggy or cloud days. The meteo folks also use them as visibility markers in winter - e.g. IceCube is something like 1km from the station by line-of-sight. Turning them off for a brief period is usually fine and we'd notify the station before we did it. On a clear night though you don't need them at all.

    If you travel to somewhere with essentially zero light pollution, like a desert, if it's a clear sky you can see with starlight

This reminds me... I need to experience this firsthand at some point. Thank you!

Question: how much (if any) of that light is due to atmospheric scattering? ie, the sun's light hitting the daytime side of the earth, being scattered in our atmosphere, and faintly illuminating the night side of our planet? Would the same be true in the zero-atmosphere environment of space?

Here are some possible answers: https://space.stackexchange.com/questions/25901/how-bright-i...

Plenty of places around the world offer dark enough conditions (but make sure it’s a new moon) - in the US you just need to get out to Arizona or Joshua Tree (or similar empty places). In Europe and elsewhere look for International Dark Sky Reserves. In general go visit places where telescopes are built.

Possible that some of it is from scattering and then if course you wouldn't get that in space as there's no atmosphere to scatter from! Scattering is incredibly faint though, even compared to starlight.

See also gegenschein and the Zodiacal light - both are backscatter effects.

Slight addendum - actually you often want satellites to be reflective. Dark means good radiator, but also good absorber and a black spacecraft is about as bad as you can get for thermal management if you point it in the wrong direction. For an Earth orbiting craft that means it’ll overheat in sunlight and then dump everything in shadow - lots of thermal stress and not good for instruments that like a constant temperature. That’s why you often see sats covered in polymide foil.

they could have sent a temporary camera along with the craft to take a picture of it at the final position and send back to earth.

How about a Tesla with Sentry cameras going?

Sounds like that would be expensive with little to no return when it comes to the goals of the mission.

Sadly one of the the problems is, it's dark where it is. The mirror side is in complete darkness (because of the sunshield), and the sun side is blazingly bright (because of the reflective sunshield).

This is the unfortunate reality of space: The images we see from the Hubble, et al, are exposed for minutes if not hours, and processed to bring out colors invisible to the human eye. An astronaut flying to see the Webb, or one of many other "well known" astronomical landmarks would see either nothing or a faint smudge without a telescope or other enhancements.

The aforementioned NASA blog post goes into the many other reasons this wasn't practical.

Yes, I get all of that, but they still missed an excellent PR opportunity. NASA really could have built some engagement showing images of the deployment process, even if the images wouldn't have direct scientific benefit. Good PR leads to improved funding which leads to more science.

I just want to make sure I understand.

Your position is that they should have added significant complexity to a maneuver that was already the most complex of its kind. A maneuver with $10 billion and two decades of work on the line. In order to make the first 30 days of a 10+ year mission marginally more entertaining.

You propose this while fully aware that the "entertainment" in question consists of things unfolding in extremely slow motion, in total darkness.

I mean, okay.

(Thought experiment: when you think about the Hubble, do you think about the day they shoved it out of the shuttle's cargo bay, or do you think about those groundbreaking images it captured during its multidecade mission?)

Literally every other nasa mission is filmed like this now. 10 billion and we can't even get visual confirmation it's doing well.

And yes. Hubble being deployed was a big deal.

Not really. There are no "selfies" of voyagers, Dawn, New Horizons, Juno etc. T There ARE pictures/data from what these have produced. JWST will be no different.

Even Hubble didnt really have any of that that I am aware of. Most of the pictures of hubble itself are from servicing missions.

Sure you have some rover selfies on Mars, but thats not the sole purpose of the instruments, quite the contrary really.

How much electrical power do you want to devote to this feel-good PR selfie camera?

According to the mission director SmarterEveryDay interviewed on his YouTube channel recently, the James Webb Space Telescope is so sensitive it could detect the heat signature of a bumblebee at the distance of the moon.

I’m pretty sure if you asked the astronomers if you could put a 5 Watt webcam on the dark side of their sun shield for the social media clicks, they’d tell you to fuck right off to L3…

If it could see a bumblebee on the moon could it detect a while on Jupiters moons ? Can anyone do the calculations ?

Well it can allegedly make photos of Jupiter that would be comparable of doing them during a close flyby, but that's likely not good enough for something of that sort. You'd have to see things through kilometers of ice.

It’s designed to see things very very far away, which are all severely redshifted. It’s mostly an infrared camera. In the human visual range of light frequencies, is camera sensors only go up to orange.

So no, it can’t detect a blue whale… ;-)

I'm wondering if there is a correlation between the level of bowing to media hype by including cameras and the actual scientific value of the mission?

The recent filming of EDL of the Perseverance rover was spectacular, but a significant aim of that mission and indeed most of the recent mars rovers has been to inspire an interest in exploration and science in the public, a significant part of that is getting happy snaps of events as they happen. The pictures taken were also of significant interest to the engineers involved as they showed events that were extremely dynamic, video being one of the best methods to gain information about the events without impacting the operation.

Web is more aimed at direct science, the products of which will, as happened with Hubble be used to make pretty pictures, which in themselves have limited scientific value, but are of enormous value in engaging the public. This combined with the difficulty and risk of capturing meaningful images given the environment makes live video a non starter.

What a condescending reply.

That 10 billion was funded by taxpayers, and the assertion that at the very least there should have been a possibility of those taxpayers seeing the fruits of their money through pictures instead of some intractable telemetry is a fair one.

    taxpayers seeing the fruits of their money through pictures

I've got great news for you! It's going to be taking pictures.

It's a telescope, you see.

NASA has often added video or image capability with low scientific value to increase public engagement, despite the associated risk and cost. They made a call not to do it this time. My only point is that it would have been a nice PR opportunity if they could have found a way to make it work within their mission parameters. I apologize if making such a simple and obvious point has offended you in some way.

This is a good PR opportunity in the same sense that you giving all your earthly possesions away to charity is a good PR opportunity :)

It's only good if you ignore the cost, and look only at the benefits.

Nope. In the category of probes/satellites, NASA doesn't put cameras that aren't needed. Probes on Mars get cameras, but that's because they're in a dynamic environment. They then use those cameras in fun, engaging ways.

As the aforelinked blog post explains, the extreme environment of the JWST makes this more challenging than it would be for missions like the Mars rovers.

The dark side of the JWST (where all the instruments are) will be operating very close to absolute zero and in near-absolute darkness which, of course, is the entire point of the mission.

A selfie camera there would need to function in that environment, while also somehow not polluting the instruments on that side of the camera with heat.

It's surely do-able, but it's a more complex engineering task (and would therefore require more tradeoffs) than operating a camera in the relatively balmy environment of Mars, where heat pollution is of no concern because of the different nature of the mission.

Keep in mind that doing this on the JWST also need to have been accomplished with decades-old technology, given the extremely long design and engineering lifecycle of a complex space mission.

I doubt adding a tiny camera is adding a significant complexity.

I see you haven't read NASA's aforelinked blog post where they explicitly detail the sorts of complexity it would add.

Since you've indicated an unwillingness to read the blog post I'll summarize briefly:

A camera on the "light" side of JWST would need its own heat shielding and wouldn't show us any of the instruments.

A camera on the "dark" side of JWST would need to function at temperatures close to absolute zero. It would somehow need to do this without disturbing the ultrasensitive instruments on the JWST.

This would have been needed to be accomplished with, essentially, 10-30 year old technology as the designs for spacecraft like this need to be locked in far ahead of time due to the incredible complexity of deep space launches.

In both cases the cameras would need power and data cable routing, and given the various harsh constraints involved (complexity, budget, liftoff weight, size) would have involved compromises in some other area.

There is no reason to use the camera while the telescope is telescoping. From what is being requested in this subthread it doesn’t even need to survive past the initial unfolding, just get a pic or two and be done with it.

I’ve read the article and I’m not criticising NASA’s decision. I’m just pointing out that a cam wouldn’t need to bring significant complexity, not in the insane context of this project.

The data it provides is enough to get funding or not, Voyager still provide data.

The excellent PR opportunity is going to be the spectacular images it produces in 3-6 months time. I have a feeling some dark grainy photos of tin foil unrolling will pale in comparison to what the device will actually product

Once again scientists miss the entire point. It is about marketing and making people interested.

It makes it easier when you go back five years later and ask for more money if people can see the multi-million dollar toy they paid for.

Yeah, scientists are point-missing dummies who think that the images that telescope will produce are of no value next to images of the telescope unfolding. Far better to have internet randos who surely aren't dummies running things.

How often do you look at exterior photos of the Hubble?

Secondly, do we collectively as smart people honestly care what the ivermectin crowd thinks about exploring the cosmos?

It’s a telescope with a camera stuck to one end. I think people will be able to see what they paid for.

When you think of the Hubble, do you think of "product porn" shots of the telescope itself, or the spectacular images and science it produced?

Likewise, for Voyager/Cassini/Huygens/etc? Don't remember any selfies from those. We merely had to settle for the spectacular, never-before-seen images of other worlds. Guess they were failures. :-(

Wow this sound so patronising. I am sure there will be a moment when they say oh wish we had installed those cameras...

Yeah, it seems like NASA hasn't really put much thought into this mission. /s

Looks like there aren’t actually any good reasons. I’m actually kind of surprised that mere curiosity at what could have been seen wasn’t good enough.

Nothing could have been seen: on the bright side, a smudge of light. On the dark side, nothing. The mirror is currently at -172° C and further cooling down toward absolute zero temperature; even with infrared it's hard to see anything at this point.

it might be "desense", that the running of electronics of certain sorts near the large detector has the effect of desensitizing it.

this is just a guess though.

Won't it be pretty close to earth in its final position at L2? If so, is there no chance that there will be future missions to do service to it? If so, maybe we can get a photo of if then?

Maybe Hubble could take a snapshot or two?

With Hubbles's highest resolution optics, the JWST will be about one-tenth the size of a pixel.

Scale. We are just a bit of noise in an impossible to understand large, complex system.

It is crazy to think about.

How can it make out galaxies at billions of light years away, but not a truck sized craft at a few million miles?

I haven't done the math myself, so I'm certain one side of that equation is wrong, but that seems hard to believe!

It’s interesting that you are expressing an opinion about something that you could calculate in the same amount of time it took to write down that opinion.

It seems like they are going for the "the easiest way to get a right answer is give the wrong answer on the internet" approach.

Cunningham's Law

https://en.wikipedia.org/wiki/Ward_Cunningham#%22Cunningham'...

To be fair, for someone who is not well-versed in either optics or space physics, calculating the answer is not that straight-forward.

You can do pretty well just comparing the ratios of the size to the distance, right? Or is it more than that?

That's a start, for sure, but to do a super accurate calculation (the kind I feel unqualified to carry out), you need to take into account apparent size, redshift, whether or not there's gravitational lensing, interstellar dust in the way, etc etc.

But I want to reiterate that what's meaningful about this discussion is in part how unintuitive things at the far edges of our scales of perception really are. It's a muscle that, left untrained, will lead you to make incorrect characterizations like the one I made.

It's been over a decade since my last astrophysics class, but I appreciate you being charitable about my assumed knowledge! I think if anything this thread shows:

1) how absolutely mindblowingly big space is

2) how bad humans really are at intuiting things at the scale of space

>a truck sized craft at a few million light years?

JWST is three light seconds from earth

Awful typo on my part! Definitely face palmed when I caught it.

Well galaxies at billions of light years distance are also 100000s light years wide. Rest of the math you can do about resolution now!

Here's the math[1]. Seems believable to me. The Web telescope is miniscule conpared to faraway galaxies, and it doesn't emit much light.

[1]: https://mobile.twitter.com/gfish/status/1479339620785524736

I did a little math of my own, and found that while the ratio of these distances is on the order of 10^15, the ratio of the sizes of these objects is on the order of 10^19.

In other words, Webb is only one TEN THOUSANDTH the apparent size of a galaxy that's a _billion light years away_

That's just mind numbing to consider!

galaxy_width / truck_width = 3 × 10^20

That is staggering. Just, wow.

Hubble can't see the Apollo descent stage on the moon either, and that is a LOT closer than L2.

TLDR: Not really. At the distance of the JWST, a single pixel on the hubble's camera is about 700m across, or roughly 30 times the size of the JWST.

The L2 point is about 1.5 million km from earth [0]. The smallest size Hubble can resolve is about 1/20 arcsecond [1]. It's in a pretty low orbit, so is effectively "on earth" relative to the distance to the L2 point where JWST is. Calculating the size of an angular measure at a given distance [2], you get about 727m [3].

[0] https://en.wikipedia.org/wiki/Lagrange_point#L2_point

[1] https://illuminateduniverse.org/2019/04/11/angular-resolutio...

[2] https://astronomy.stackexchange.com/a/20728

[3] https://www.wolframalpha.com/input/?i=tan%28%281+arcsec%29%2...

It's not that close. The moon is 384,400km away, and JWST will be 1.5 million km away (i.e., around 4x as far as the moon). It would be a pretty serious undertaking to get to it and get back.

Distance isn’t the best proxy for difficulty of a space mission. The delta-v to get to low lunar orbit is higher than the delta-v to get to L2. The delta-v required for lunar landing is considerably higher. And all of these manoeuvres are much less than the delta-v required to get to LEO.

That depends. If we're talking a manned service mission, then distance is a factor as it would mean a several month trip using current vehicles.

That being said, and I haven't done the math, but I think a Falcon Heavy and Dragon could do it at least in terms of delta V; although there are numerous problems with that like the fact that the dragon doesn't have a proper airlock for starters.

No L2 is on the further side of the moon.

Maybe when we have active bases on the moon or Mars would a rendezvous with L2 be feasible but not before. Hubble is in low earth orbit and far more accessible.

Not exactly. Actually it's on the opposite side of the Earth relative to the Sun. So the 3 are always on one line but it has nothing to do with the position of the Moon. (Maybe you thought it was at the L2 of Earth-Moon system?)

Oof, I knew that. JWST is at the earth-sun L2, that fact just didn’t enter my mind trying to figure out how far away it was.

L2 is 1.5 million km away. For perspective, the moon is 384 000 km away. That's nearly 4x the distance. It took Apollo astronauts 3 days to reach the moon.

So it will take almost 2 weeks to get to JSWT, and two weeks to come back.

Presumably such a mission would be unmanned and therefore a one-way trip.

Given that SpaceX is hoping to start initial Mars missions by the 2030s and JWST is expected to last much longer than 10 years due to fuel savings on the L2 injection burn, it wouldn't be too outlandish for a servicing mission to be attempted by then, a vehicle capable of the 3-6 month trip to Mars is obviously capable of a 2 week trip to L2 and back.

On the other hand, with how delicate the optics and sunshield are, a servicing mission might not be worth it. At that point NASA might find it more productive to build a larger telescope, except this time it could again be designed to be manually deployed and serviced, thus not needing the complex automated deployment that delayed the JWST so much.

the plan as i understand it is to have a drone refuel it after about 10 years or so... that might have a camera on it perhaps?

I thought there were no plans for any refuel or repair mission.

There are no plans at the moment because it is not even clear how long will current fuel supply last. NASA engineer today said "maybe 20 years, roughly speaking", my back-of-napkin math says that it could be up to 30 if everything goes great. It will depend on exact schedule of observations, number of unexpected transient observations and solar activity. Computer simulations of its orbit and solar wind pressure have some error bars that will be corrected once we get solid data. It also has funding for only 5 years of ground operations right now. Once the mission get extended and we have solid understanding of how it behaves in space we could think of designing refuelling mission. It has fuel port so it is possible in principle, but I don't expect any concrete plans within 10 years.

Yeah, I think that will depend on the scientific quality of the observations provided by JWST:

- Hubble/COBE level. Refuel it!

- LHC level: Meh, let it rot.

Tbf it is less about the device (and the people working on it) and more about what kind of fundamental changes to our understanding of the universe is provided by its observations. BTW I am pretty bullish on that front.

I guess the videos I watched made it seem more sure than it is... at the very least they left themselves open to the possibility of it if it makes sense to do.

Why dont we deploy a smaller sat in the same-ish orbit thats only job is to be the RING Doorbell for the JWST -- all it does is stream a live-stream back of the JWST -- if we can freaking deploy streams of Starlink (SKYNET) devices - we can certainly place tele-photo-capable sats that can then provide streaming video back of the things they are walking -- and they can FN relay off the starlink (SKYNET) devices...

All you would be able to see is the sunny side of the sun shield, none of the cool (both literally and figuratively) bits, which are all in darkness.

I have a few questions about extending a tethered "selfie bot"

If you have a tethered camera which uses the tether as its power source which is out in front of the scope, wouldn't it be able to "stare" back at the Business Side of the mullet and stream the Party back to earth?

Or does a teathered bot risk messing with the orbit of the scope?

How much actual pull strength is requireed per kilo to re-orient something in space, meaning: How easily could say an astronaught pull on a cable and change the orientation of an object of much larger mass?

What if there were a gyro-ratchet:

Gyros that spin, and are tethered to a thing. There are multiple of them and they "yank" a small amount by spinning their gyro/flywheel a bit to initiate a pull... but there are many of these extending off tethers to orient something...

What if the tethers are like a flat ribbon cable of super thin solar collecting "flat noodles" - they provide power to the orienting gyros...

but how do you untangle things in space if stuff goeas awry...

---

Maybe the craft only deploys gyros, via tethers, when it needs alignment - re-pointing... and reels the gyro back in when done...

or reels them back out when the tether should use solar to trickle re-charge the gyro battery.

But what would the point be? All the interesting bits are in effectively total darkness.

>>But what would the point be?

But why should imagine anything?

But that's literally all we would be doing... imagining... You could accomplish exactly the same thing by leaving the lens cap on a camera here on earth. It would see just as much of the interesting parts of Webb as a camera 20m beyond Webb's orbit looking back at it.

Totally not related to the thread, but I think you would like looking into certain aspects of etymology...

Specifically the terms HollyWood (where that comes from is Pagan Druids, as that is where they took their Wands from which CAST SPELLS... Tele-vision, broadCASTING, Programming -- etc, its all there...

Spelling - to create/cast - cast as into formation....

Imagining --- is an interesting word...

even if its looking at the business side of the telescpe the sun sheild means there is no light there for it to be able to see anything.

its a case of your can't see it because there is no light, not because you dont have an angle of it (although that is also a chalange to overcome.

Nothing to see here folks, move on.

Because it’s not interesting looking at a big sheet of tinfoil in space. It also would be quite likely that the two would run into each other.

And JWST is really far from earth, starlink would do nothing.

Maybe Hubble could be used to take images of it?

One of the big numbers that been thrown around is that JWST has 344 single points of failure in its mission. Now that deployment has been completed, is there somewhere that lists how many of those points we have passed?

Not sure about the points of failure, but according to [1] only four deployment stages remain. So the large majority of point of failure should have been passed already.

[1] https://jwst.nasa.gov/content/webbLaunch/deploymentExplorer....

>344 single points of failure

How can a system have more that one single point of failure?

If you're in a car being held above the ground by a chain, every single link is a potential single-point of failure.

What a fantastic comment. In a visual and immediate way to explain such a complex concept in one sentence.

But the chain itself can be considered as one component and it becomes a single point of failure. Or if we go in the opposite direction, then we can breakdown links and say "Every single grain boundary is a single point of failure".

Partially-agreed on the former, but not the latter.

So long as the chain is not loaded near its tensile limit, then the grain boundaries that support the load within each link do so in parallel and are therefore redundant.

The selection of the allegory of the chain was intentional -- each link must be properly formed, or the entire chain will fail. If it breaks, it is surely correct to say, "the chain broke", but in truth, it was actually link-86.

For JWST, the remarkable/audacious thing is that many links in the chain from launch to observation are potential single-point failures. Furthermore, many of them haven't ever been tested independently in space... ever. It is a hell of a triumph that JWST has gotten this far already.

If even a small fraction of the instrumentation works at this point, we are going to learn a ton about the universe, simply due to JWST's position, collecting-area, and mirror-diameter.

You're right. I think I was searching for a better analogy. Abstractly: Sub-system SPOF conditions can be bundled up as a single System SPOF condition by multiplying the probabilities.

Also, I don't want to underplay JWST's success or its challenges. But, when saying 300+ SPOF conditions, one has to specify at what abstraction level. Otherwise, it can be misleading.

Each link in the chain is itself manufactured/created/constructed. If the weld is bad, the link may fail. "every grain boundary" is not formed in the same way each link is. The analogy is solid - actually, it's very good in that it conveys clearly and succinctly the concept the parent was asking about without introducing extraneous concepts. Very much in the flavour of EWD: "The purpose of abstraction is not to be vague, but to create a new semantic level in which one can be absolutely precise."

Another example is a small single engine airplane. The engine can be considered a single point of failure but if you zoom in it’s a complex system with many redundant components (multiple cylinders, multiple spark plugs per cylinder, etc.)

A system may be implemted as a set of cooperating microservices each one being a (single) point if failure of the entire system.

Like many Node dependencies

Contrast a chain with double links, where if any link fails another is entirely capable of holding the load.

In a real chain, only one link is actually the weakest, and it is at that link where the chain will break, in the hypothetical you offer.

Which is true, but also not what's being discussed, which is "single point of failures", not "weakest link".

That’s not correct, someone with a bolt cutter can get any link in the chain and it causes collapse.

Single point of failure doesn’t mean “weakest link”. It means if this one piece (“single point”) fails, the whole system will fail.

But you don’t know which, and others may fail first due to various adverse events (say, random micrometeoroid strike). If any link fails, the whole chain fails.

Contrast a second chain, or double linked chain, so if any link fails the load is not lost.

This assumes the environment is completely predictable.

If you know the strength of every link in the chain with perfect accuracy, and you know that the only potential cause of failure is too much weight being placed on the chain, then the only link that can fail is the weakest[1] one because no other failure can happen before that one.

But really you need to design for the idea that various things might happen. Someone else gave the example of a person choosing a link to cut with bolt cutters. The person's choice is what's not predictable in that example.

---

[1] And if you assume it's not possible to have two links that are exactly as strong as each other.

"only one link is actually the weakest"

Which isn't relevant since (obviously) no one was talking about how many links are the weakest link.

"it is at that link where the chain will break"

Wars have been lost by thinking this way. e.g., D-Day was a successful assault on a strong link.

The classic counterexample to the chain (where each link is a SPOF) is the braided cable or rope, in which each individual strand shares the load collectively, and loss of some fraction of the total strands won't itself cause failure.

That's not to say that cables or ropes cannot fail, but when they do so, failure of many individual components is required.

A recent example is the failure of support cables for the Arecibo radio observatory in Puerto Rico in 2020. This was the result of a progressive failure played out over months, though at an accelerating rate, until the final catastrophic failure and loss of the instrument as a whole. (This wasn't wholly unforseen and was precipitated by a long period of rather intentional neglect of maintenance.)

Even after the failure of two complete cables, the remaining cables supported the load of Arecibo's instrument platform. On 1 December 2020, strands of one of the remaining cables began breaking, at an accelerating rate, leading to the total failure of that cable, then a second and third, and with it loss of the instrument platform. The final moments were captured on video.

Sequence begins at about 55s here: https://yewtu.be/watch?v=b3AASKr_iHc

Thank you for linking to one of the invidious instances. Youtube itself has become so annoying it's no longer workable for me.

The sequential deployment process had many possible individual points of failure along the way - if any step went wrong then the full deployment failed.

well yes, but wouldn't we refer to them simply by "points of failure" not "single"?

I think it's single in the sense that only a single failure in any of those points would render the entire project a failure, not that there's only one point that can possibly fail.

Contrast, say, a single-engine jet plane with a twin-engine jet plane that can still make it to the airport safely with the remaining engine, should one engine fail mid-flight.

"single point of failure" is a phrase that refers to any subsystem which the whole system is dependent on.

Most failure points on Webb have redundancies. So their failure doesn't brick the telescope, both the part and its redundancy have to fail before Webb is bricked. The single points brick Webb with only a single failure.

Because a point of failure could have multiple redundancies, and in this case they did not, every one of those points was implemented in a non-redundant way.

It's a point where a single failure causes system failure, but that's a lot more words. These things tend to get whittled down to "terms of art", the meaning of which is understood by those trained in the art. It's perhaps best to just call it an SPOF and then people will hopefully google it to find out what that means.

I think linguistically the term can be hard to parse.

If any one of 344 pieces were to fail during deployment, then all of the deployment has failed and the entire $10B was a loss. Consider the engine in your car- how many single pieces of it could fail before the entire engine can't work? The difference with Webb is that most of those points were single actions that had to work once.

And we're now at a stage where most of them did not fail.

"A single point of failure (SPOF) is a part of a system that, if it fails, will stop the entire system from working."

>I think linguistically the term can be hard to parse.

Yeah, "solitary" might make more sense ... or "non-redundant". Or "point of single failure".

I think SPF means a construction where there's no redundancy provided? Though it does raise the question of how this is counted: table with 4 legs, any of them breaks, table is still standing. Table with three legs, any of them breaks, table is broken.

Airliners are designed so that no single failure can bring it down.

That's not entirely true. Any reasonably complex system will almost certainly have single points of failure, including airliners. Those single points of failures might be very unlikely, but they are still there. E.g. what if the front fell off?

It is entirely true. Source: I worked on 757 flight controls design for 3 years.

> what if the front fell off?

All structural components are redundant and have redundant attachments. The wing spars are doubled, for example.

There are certainly single points of failure in airliner design. An example that springs to mind is the stabilizer trim jackscrew. There are supporting systems which try to mitigate the risk of failure or the likelihood of failure, but bottom line, if the jackscrew fails, there is no redundancy. You've lost stab trim, potentially making the situation unrecoverable. Of course Alaska 261 is one such example of a jackscrew failure.

I worked for 3 years on the design the 757 stab trim jackscrew. We considered every failure, and had redundancy for it.

The AL flight cracked its nut, and the balls fell out. I don't know the details of that design, but on the 757 the ice scrapers on both sides of the nut will hold the nut in place if the balls fall out.

If I recall correctly, if the AL pilot had simply left the trim system alone after it failed, and landed the airplane, it would have been fine. Instead, he kept fiddling with it, driving it up and down, until it tore the nut to pieces. The loud screech it made when running in a half broken configuration should have chilled anyone's blood to bone at 30,000 feet.

As that incident, and the later MAX crashes clearly demonstrated, once something goes wrong with the stab trim system, you move it only enough to get the airplane into a flyable state. Then, you turn it off and leave it the frack alone. Land it, and let the mechanics figure it out with it safely in the hangar.

One incident where the stab trim failed and the poor pilots were just passengers to their doom was that 747 that took off from the base, and some tank in the cargo hold broke loose, slid back, smashed through the bulkhead and broke off the whole stab trim system.

That really wasn't the stab trim system's fault, you can't really design for a tank falling on it. It was the fault of no redundancy in the straps holding the tank in place.

The video of the crash, shown endlessly on the news, makes my gut turn to water.

I fully agree that the risk tradeoffs made on these designs are highly unlikely to fail. The point is, though, that if they DO fail there IS NO redundancy. There aren't two jackscrew mechanisms. It's a single point of failure. Highly reliable single points of failure don't become redundant because of their high reliability -- they are still single points of failure. And sometimes those must be accepted -- even in safety critical systems.

Tell that to the passengers on the two 737 MAX planes that crashed.

Single point of failure is a term for non-redundant, critical parts of a system:

https://en.m.wikipedia.org/wiki/Single_point_of_failure

Are these 'points of failure' ? not single points of failure? I assume some of these have redundancy but could fail.

In your body, the brain, heart and lungs are all single points of failure.

If either one fails, you die.

You have two lungs, though. One can fail and you will still live. As with kidneys. Strange that there is only one heart.

It's strange but we're still pretty bad at using more than a single computer core on average.

Lungs and kidneys can work independently, but two pumps running at the same time on the same circuit will cause more failures ... it's like parallel vs. sequential circuits.

There are 344 individual items that can make the $10 billion satellite be a paper weight in orbit. Those are the very definition of single points of failure.

BY the phrase not meaning what you think it means.

https://en.wikipedia.org/wiki/Single_point_of_failure

"A single point of failure (SPOF) is a part of a system that, if it fails, will stop the entire system from working."

AFAIK no single mirror segment failure would destroy the entire telescope, so the only one still on the future is the L2 insertion burn.

As always, it's useful to post this link:

https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html

Since L2 is an unstable equilibrium, won’t there also need to be routine adjustments throughout the mission?

Yes.

Those adjustments, as well as unloading of the reaction wheels used to position JWST, and the fuel burns reqiured for them, are the principle determinants of the JWAT's lifespan, estimated at 10 years.

Nasa have lowballed such estimates for numerous missions in the past (Hubble and numerous Mars lander and rover missions come to mind), and it's possible JWST will exceed the planned lifetime, potentially by a wide margin. Initial indications are that the Ariane V insertion should have spared much potential fuel use in orbital corrections and insertion.

I expect the space geek set will have speculation, hopefully reasonably informed, on this in the not-too-distant future.

Apparently the launch and mid course burn were precise enough that it should have enough remaining propellant for a bit more than 10 years of station keeping.

Thought the same. The launch and everything went down so perfectly I bet it gets more than 10 years.

I was under the impression that they were planning on making a drone that would refuel it in 10 years or so? Is that not correct?

I've heard that the capavility exist but the mission is not planned.

https://www.space.com/3833-nasa-adds-docking-capability-spac...

https://jwst.nasa.gov/content/about/faqs/faq.html#serviceabl...

They have given it a 10 year lifespan. They have said that fuel is a major limiting factor and talked about a refuelling drone to extend life.

But I don't think that means it only has 10 years of fuel, and I don't think they have ever said explicitly said that. I suspect it's more like 15 years in the best case.

The fact that they aren't already planning a refuelling mission implies that it's not a critical limiting factor.

Would I be wrong to assume that technological advances in the next 15 years would justify sending a second satellite? As in, instead of a refueling mission we'd be more likely to send a version 2 of the satellite with even better sensors/apparatus/whatnot?

jswt was the version 2 satellite for hubble. turns out we were able to do 4 massive upgrades to keep hubble relevant before hubble v2 got anywhere

It's helpful to think through what opportunities might exist.

There are a set of telescope plans which are presently in consideration, including WIRST, the wide-angle infrared telescope; HabEx, the Habitable Exoplanet Imaging Mission; Lynx, a next-generation X-ray telescope; and the Origins Space Telescope, an infra-red telescope even larger than Webb.

https://www.universetoday.com/139461/what-comes-after-james-...

For telescopes, among factors I'm aware of are:

- The total number of devices. More 'scopes means more points of the sky which can be imaged at any one time. This permits detecting either rare or transient events.

- Wavelength specificity. Infra-red, radio, visible light, UV, and X-Ray sensitivity all permit detection of different phenomena. Devices suited to one wavelength may not be suitable for others. Specific research goals may favour specific observational methods.

- Other sensing modes. Gravity, gamma ray, and particle sensors (e.g., neutrino sensors, cosmic-ray detectors) may afford other options. There are proposals for space-based gravity-wave detectors, for example.

- Compound devices. The HabEx system in particular has two components, the telescope itself, and a sunshield used to block the light of an observed star, which would operate at a separation of 100s of thousands of km.

- Collector size. Larger mirrors permit gathering of more light. This permits shorter collection periods for brighter events, and imaging of previously undetectable phenomena. The Hubble Deep Field views are an example of the latter, and pushed the boundaries of known and and observable phenomena tremendously.

- Storage, processing, and communications capabilities. I don't know how much this contributes to observation capabilities, though I suspect it has an impact.

- Developments in phsyics, materials, and sensing, generally. Looking through lists of physics and chemistry Nobel awards since the 1970s, a surprisingly large number have concerned capabilities rather than fundamental characteristics or properties of matter or the universe. Many of these afford new capabilities in sensing and detection.

- Probes. Rather than a single instrument which views distant objects, probes get close to a specific object, or set of objects, and make close or direct observations of these. Various landers, impactors, flyby, orbiter, and similar missions, to date all to objects within the Solar System, would be examples of these. These compete with other missions (manned, long-distance sensing).

- Earth observation. Probably the largest class and most productive set of space-based observation platforms has been looking at our own planet.

It's also worth thinking through what has made JWST possible, including launch platforms, experience with complex deployments, manufacturing, sensing, and control capabilities. These will have impacts on future missions, and further development might also extend their capabilities.

Finally: most technological improvement tends to follow a sigmoidal curve: an early period of slow development, a period of rapid attainment, then a slower period of approaching theoretical maximum efficacy. New developments or combinations of technologies may restart that curve, but often 15 years doesn't deliver transformational development. Rather older technologies are refined, reliability improved, costs reduced, or flexibility increased.

They are already ahead on their fuel budget due to the accuracy of the Ariane launch process. NASA said it would "significantly" extend the mission lifetime.

https://blogs.nasa.gov/webb/2021/12/29/nasa-says-webbs-exces...

Of course, nothing is perfect they will have to adjust position over time and have accounted for all of it with possible robotic missions in the future to extend and refuel as necessary, although that is a "hope" rather a surety.

Does anybody know exactly how unstable L2 is?

I've seen lots of people talk about how some Lagrange points are stable and others are unstable, but I've never been able to find a source for how much this matters.

How long would it take for Webb to move so far off L2 that we can't communicate with it anymore, or for it to be at risk of being completely thrown out of orbit to the point that it would impact earth or the sun?

It matters enough that "over ten years" of fuel left (as we supposedly have now) is a really great outcome, as opposed to just five we might have form. Scott Manley on YouTube has a pretty good video on Lagrange points (and it's a topic where the video medium is actually pretty helpful).

The failure mode of straying too far from L2 is the inability to shield the highly sensitive optics from both the Earth-Moon system and the Sun simultaneously.

> Mike Menzel: 49 of the 344 single point failures remain and will remain throughout the mission. They are the same types of things on every mission, like propulsion. 15 are related to the instruments.

https://twitter.com/SpcPlcyOnline/status/1479900221131964421

Can anyone elaborate on these single points of failures? For example, are they actually single points of failure? Or is it a bit of exaggeration for marketing purposes (a bit of under promise, over deliver)?

There is a bit of exaggeration, for example non-explosive actuators that needed to be released for sunshield to deploy have two redundant electric circuits for their deployment but are considered 'single points of failure' as compound part. Propulsion system is also considered SPoF but there is some redundancy built in, like there are two independent sets of thrusters feeded from one fuel tank.

Some other parts don't and cannot have redundancy due to design.

They are single points of failure.

That's not much of an elaboration. Further, I am doubtful, because something always goes wrong. So if a project that has seen decades of delays and billions of dollars of budget overruns has suddenly invented engineering and processes that yields zero failures, count me surprised.

I just wish there was more elaboration of things they are able to accommodate for as things inevitably pop up and not this hyper focus on a number of supposed single point failures.

A lot of them are "optional" but strongly preferred. E.g. if one or two of the mirror wings failed to deploy, JWST would still be usable, but with a degraded resolution.

If one or two layers of the sunshade failed to correctly deploy, JWST is still usable, but the temperature of the mirrors would be higher than expected, and thus the spectrum of IR light it can image would be reduced.

If the momentum flap fails to deploy, then more fuel is needed to keep the JWST at the right attitude/position, shortening the lifespan of the mission.

But some others were make or break: deployment of the solar panels, deployment of the secondary mirror and a few others. If those had failed then the mission would be over.

It’s probably an internal list of serious things that could go wrong. There’s a lot of bike shed discussion here about what a “single point of failure” should include.

I think it's one of the greatest engineering results ever, a 6 meter infrared telescope 1 million km away, just wow!

1.4, not that that is a difference in degree, but it is somewhat relevant.

What puzzles me is the maneuvering fuel. When that fuel runs out, the telescope can no longer orient itself. This ended the life of the Kepler telescope.

But aren't there other ways to orient in space?

1. use pressure from the solar wind

2. have 3 electric motors on 3 axis. Wouldn't spinning those motors rotate the craft? Electric power to do it would come from solar panels, giving it plenty of fuel.

IIRC the thrusters are also used for station-keeping since practical Lagrange orbits are unstable.

Being a telescope, what matters is where it is pointing, not where it is.

It matters a lot, L2 is unstable point so if it ventures beyond L2 there would be no way to bring it back and it would enter a heliocentric orbit. Communication between Earth and telescope would become impossible after some time as gimballed antenna can only rotate so far and stray light reflected from Earth would limit its field of view.

Due to that JWST will always be on 'close side of L2' and technically in slow freefall back to Earth and boosted up periodically, but always a bit short of passing to the other side.

> as gimballed antenna can only rotate so far

That's a fixable design problem. Or you can rotate the telescope.

> stray light reflected from Earth would limit its field of view

What? The earth and the moon are nearby anyway. What about that reflected light? And heck, what about the sun limiting its field of view?

Actually you can't rotate the telescope; they managed orientation even through the launch because if some of the science instruments get pointed towards the sun for too long they'll be destroyed. Now that it's deployed it's even more important that the cold side stays cold.

> That's a fixable design problem.

You are right, it is fixable. It was fixed by adding active station keeping to the telescope.

> Or you can rotate the telescope.

There are limits on its rotation with respect to the Sun, dark side must be kept away from sunlight at all times. It can rotate 5 degrees "pitch down" toward the Sun and 45 degrees "pitch up". Gimballed antenna has enough authority so that it can communicate with Earth at whatever valid rotation telescope is so that science operations are not interrupted for transmitting data.

> The earth and the moon are nearby anyway. What about that reflected light? And heck, what about the sun limiting its field of view?

That light is reflected back by sunshield as all 3 bodies are behind it. Sun is limiting field of view but area of exclusion changes as telescope orbits and it can image every point in the sky at least every 6 months and 39% of the sky at any given moment.

Could they put up some relay sats?

Reaction wheels let you orient but they don’t allow you to maintain an orbit.

not sure about 1, but it already orients itself using reaction wheels, which are basically what you are describing with 2.

The issue is that its position at the lagrange point L2 is an unstable equilibrium, which requires occasional adjustment using thrusters. In terms of gravitational potential energy, its position in space is a saddle point, not a local minimum.

They've already mentioned having more than the of amount of manoeuvring fuel (or, as we should really be calling it, delta-v) they had planned to have left at this point. Space craft have a limited life time anyway (CCD's wear out, semiconductors are subject to electron migration, solar panels degrade), so having a limited amount of fuel to stay at Sol-Earth L2 is just part of the whole lifetime equation.

Right, but NOVA said that running out of fuel ended Kepler.

It worked for 9 years and 7 months, whilst being planned to operate for 3,5 years, so beyond it's expected lifetime then.

And it would have worked for longer if it didn't depend on the fuel!

BTW, I doubt there's enough experience with space hardware to accurately predict it's life, especially since each machine is a one-off.

It would have lasted a lot longer if its reaction wheels hadn't failed. That was the main failure which shortened its remaining operation.

You'd need at least 3 wheels to orient the craft. I bet that 4 wheels would be able to survive the failure of one.

Kepler had 4 wheels, with 2 failing

Pressure from solar wind will constantly put some torque onto telescope as its center of pressure is offset from center of mass. This torque will be counteracted by reaction wheels but they have maximum rotation speed and need to be unloaded using thrusters periodically.

A rudder would work to counter any torque from the solar wind, and can be used to orient it.

Thus, the "Aft Momentum flap":

https://www.jwst.nasa.gov/content/webbLaunch/deploymentExplo...

Momentum flap will bring average CoP closer to CoM but CoP will shift as JWST is rotated to point at different targets. Unwanted torque can be minimised by carefully choosing observations targets so it mostly cancels out but it cannot be done perfectly.

I wonder if the target scheduling will take that into account to minimize average drift? Interesting set of calculations...

> As an additional challenge, the JWST observation schedule in the next 21-day period will not be known at the time of SK [station keeping] maneuver planning. A planned observation schedule one week ahead will be available, but the actual observation schedule will be event-driven. If a ‘target of opportunity’ arises then the schedule can be changed within 48 hours to point at the new target.

https://ntrs.nasa.gov/api/citations/20140007519/downloads/20...

JWST, like many other spacecraft, has reaction wheels to orient itself. The reason Kepler ran out of fuel when it did was that it was expending more maneuvering fuel for attitude control because two of its four reaction wheels failed. Hubble and the ISS also had similar failures.

We're getting better all the time at building more reliable components (including reaction wheels and cryocoolers) though. Until a few years ago, the life of something like JWST would be limited by the amount of liquid helium on board to cool the components. Modern cryocooler technology (aka a space grade refrigerator) is good enough to cool it indefinitely. Solid state cryocoolers, previously unachievable, are now apparently available for some applications (important not only for reliability but also to reduce vibrations).

Reaction wheels can be used for attitude control but they still have to be unloaded by thrusters after maneuvering for a while. You're right that you could use a rudder (probably two rudders would be required for 3d attitude control) and have to have a balanced solar wind profile (JWST does actually have a solar wind balancing flap, but I don't think it's adjustable like a rudder). But solar wind won't act fast enough if you want to quickly change attitude for observations. And you can't use reaction wheels for stationkeeping. It very much matters where the telescope is, since if it drifts too far away from Earth it will be much harder to send high bandwidth data, and if it's too close to Earth, Moon etc. it will have no way to orient without heating up or blinding itself with the IR sunlight reflected by them.

> The reason Kepler ran out of fuel when it did was that it was expending more maneuvering fuel for attitude control because two of its four reaction wheels failed. Hubble and the ISS also had similar failures.

And to calm down anyone afraid of JWST sharing the same fate - construction of reaction wheels have been changed some time ago to make them significantly more reliable. The source of issues on Hubble, Kepler, FUSE, Hayabusa, Dawn and TIMED was electrical arcing between metal parts of reaction wheels. Static charge was building up like when you rub a ballon against your head. That charge caused arcing that in turn caused metal pitting and increased friction leading to failures. That failure mode was understood only in late 2007, when Kepler was already fully build and ready for launch.

JWSt uses new generation ceramic bearing in its reaction wheels, they have been used in spacecrafts since 2010 with great performance.

Great info: citation? More details?

Here is a paper detailing metal reaction wheels failure modes going into detail on how charge was built up and solar influence on this process: https://www.esmats.eu/esmatspapers/pastpapers/pdfs/2017/bial...

I cannot find primary source for JWST using ceramic bearings right now, but I know they are manufactured by Rockwell Collins Deutchland and have good track record: https://jwst.nasa.gov/content/forScientists/faqScientists.ht...

TELDIX (today owned by Rockwell Collins Deutchland) invented use of ceramic bearing in reaction wheels for spacecraft use in 1978: https://patents.google.com/patent/DE3027209A1/en

so it would make sense that JWST uses ceramic bearings. Other manufacturers (ITHACO) have switched to ceramic too.

Scott Manley video: https://www.youtube.com/watch?v=KibT-PEMHUU

> JWST, like many other spacecraft, has reaction wheels to orient itself.

It should be noted that reaction wheels can saturate when the motor reaches its top speed. One then needs to spend fuel to provide a counter-force while the wheel to spins down.

So even with reaction wheels running off solar panels or similar you need fuel, though much less.

That's what "unloading" the reaction wheels refers to in some comments here, in case others were wondering.

Perhaps in a future design the reaction wheel could be unloaded by solar rudder, reducing the need for maneuvering fuel (although station keeping fuel would still be required without an outright solar sail).

edit - apparently they do do something like this? https://news.ycombinator.com/item?id=29857031

As far as I can tell it only really needs the fuel to maintain an L2 orbit, which is important because if it's too far away we can't really communicate with it effectively (i.e. actually download much of the data it's generating). For orientation it uses reaction wheels as you mention, and then there's a general plan to desaturate these momentum wheels by managing the average orientation of the telescope (it's effectively like an inverted pendulum: the solar wind will push it further away from having its back to the sun), but this might intefere with some observations so they may burn some fuel to maintain orientation in certain circumstances.

https://space.stackexchange.com/questions/35399/how-will-jws...

Kepler used a similar strategy (though I don't know what its desaturation strategy was): it only ran out of fuel very quickly after its reaction wheels failed.

They should have made a port for refueling it.

An internal fuel tank and a high-capacity tank externally

Once the fuel is getting low, launch a refuel. when the new supply gets closed, eject the previous tank, dock the new one.

Easy.

When they managed to du an in air refuel of a SR71 in 1970s . Surely we can dock a fuel tank in 2022?

And besides, it works in kerbal space program.

> Easy.

Nothing in space is easy.

They did:

"Unlike Hubble, Webb isn't designed to be fixed by astronauts. But it can be refueled robotically. Zurbuchen says that 'once this telescope is deployed, I'm going to put all the effort towards developing that technology, and so within the 10-year lifespan, we can go refuel it'"

https://nitter.42l.fr/marinakoren/status/1474367236244750345...

https://nitter.42l.fr/Dr_ThomasZ/status/1474398711505580032#...

awesome :) Thank you.

The astronauts had some serious, unexpected difficulties fixing the Hubble in orbit, and had to improvise. I'm skeptical that blasting a fuel coupling into space, and then trying to figure out how to connect it to a robot, will end well.

I don't know. If the fuel coupling design is compatible with robotic access, it might be doable. That would seem easier than the dozens of repairs that astronauts did with Hubble. I assume we learned a lot with the Hubble servicing missions, some of which will be applicable to robotic work. The full list of Hubble service/repairs is quite remarkable if anyone is interested:

https://hubblesite.org/mission-and-telescope/servicing-missi...

Press release with more details: https://www.nasa.gov/press-release/nasa-s-webb-telescope-rea...

Ok, we've changed to that from https://twitter.com/NASAWebb/status/1479880178021060609 above. Thanks!

For some context around what makes this deployment so remarkable, watch this[0] video that talks about the engineering/building aspects of the James Webb [0] https://youtu.be/aICaAEXDJQQ

Thanks for the link. I am interested in knowing more about the organization behind that project: how many people took care of the deployment, how are they organized, how has quality control been done.

https://www.latimes.com/business/story/2021-12-25/james-webb... gives some info but not an in-depth view of how things work at the NASA.

A couple of interesting links I've found so far on the technology of the telescope.

https://www.jwst.nasa.gov/content/observatory/ote/mirrors/in...

https://www.stsci.edu/~idash/pub/dashevsky0607rcsgso.pdf

https://ntrs.nasa.gov/api/citations/20080030196/downloads/20...

Thank you, this is great, have been looking unsuccessfully for technical content like this.

What I love about this project is that I had an active worry about its success, very few things in life inspire that kind of emotion. Well done to all involved, a true lifetime achievement. Can't wait for the images!

The cost: 23 years and $10B

The benefit: “JWST’s instruments are designed to make discoveries across the spectrum of astronomy — ranging from the worlds and mini-worlds in our own solar system to alien planets circling distant stars, from the supermassive black hole at the center of our own Milky Way galaxy to the edge of the observable universe.” (https://www.geekwire.com/2021/high-cost-high-risk-high-hopes...)

Extremes on the cost/benefit helped create some extreme emotions, I agree!

I don't understand why is it considered extreme cost. IIRC it's around $1/us citizen/year. For example the budget for keeping us safe from ourselves is much higher.

That's a great point, Makes me wonder what long term projects my own government have. Does anyone know of other inspiring long term projects in progress? The ITER fusion project is one that comes to mind.

You could probably find any by searching your country's name here: https://en.wikipedia.org/wiki/List_of_megaprojects

It seems to cover all sorts of categories, and the James Webb Space Telescope is there (though listed as still under construction).

So it is cheaper than most of recent Olympics. More benefit as well.

Right, but I think the risk factor as well makes it emotional. There was a non-0 chance that it could be unrecoverable and we could get 0 use of it if one of the points of failure went wrong.

To me the second most exciting idea about JWST is that it might give us fairly definitive proof that other intelligent life exists in the galaxy.

The most exciting idea is if that happens we'll realize they might have built their own version of JWST and proven we exist.

How so? What technology specifically would give the JWST an advantage in discovering new life? Genuinely curious.

1. Its resolution might be high enough to image [big] surface features on exoplanets, and alien megastructures if they exist[0].

2. JWST has extraordinary spectral analysis capabilities and it should be able to characterise gases in extrasolar planetary atmospheres [1].

[0] https://www.popularmechanics.com/space/telescopes/a19346/jam...

[1] https://www.jwst.nasa.gov/content/science/origins.html

Heh. Can you imagine the world-wide debate over whether or not we should reach out to the alien intelligence?

Apparently, SETI's policy is to NOT respond. Which makes sense to me.

Looking for intelligent life or hoping we’re found by one is likely very foolish. To me, the dark forest theory is the most compelling explanation for the Fermi paradox.

Something I am wondering about the L2 orbit ... per NASA:

> Webb's orbit [~ around L2] ... is actually similar in size to the Moon's orbit around the Earth! This orbit (which takes Webb about 6 months to complete once) keeps the telescope out of the shadows of both the Earth and Moon. Unlike Hubble, which goes in and out of Earth shadow every 90 minutes, Webb will have an unimpeded view that will allow science operations 24/7.

https://jwst.nasa.gov/content/about/orbit.html

Wouldn't remaining in Earth's shadow result in less interference, with Earth providing an extra sunshield? And "an unimpeded view" of what? I can't believe those cold, sensitive optics, with that carefully engineered sunshield, will point anywhere but away from the Sun.

> with Earth providing an extra sunshield

Maybe it needs the sun for its solar power?

> And "an unimpeded view" of what?

If hubble is looking at sometihng not perpendicular to its orbit, during half the 90 minutes the target will be "behind" the earth, right? So it can only look at things that are to the left or right of its orbit.

The advantage of L2 is that the sun and earth will always be in the same direction (more or less) so it's easy to cancel it out. I don't think there's an orbit that would stay in Earth's shadow constantly that would have the same properties (without needing a ton of fuel)

I think it needs to get some sun to power the solar panels, right? No sun = no electricity = no science.

Congratulations to the team, it's been a long road but it's satisfying to see so many folks efforts paying off.

I remember seeing a full size mock up of the JWST nearly ten years ago, and thinking it was just too big, complex and far out to succeed. But dedicated people made it happen.

It says it will arrive in 14 days or so at L2.

Right now, it is moving 0.3933km/s which according to Google is 1415.88km/h. That is pretty fast.

What speed does it need to be at for insertion and steady state? How long will it be breaking? (If at all, or of it is not already doing it).

About 0. It’s climbing a hill and has just enough energy to get to the top. A small burn then will be all it takes to put it in an orbit around L2.

It also needs to get as close as possible to the top of the hill without going over. L2 is not a stable point: you’re either falling back to Earth or drifting away. If it goes over it can never get back as it can only fire in one direction - away from Earth (to protect the instruments from the Sun). So it’s a continuous balancing act where it falls downhill towards Earth a bit, then jumps up without going over the edge, rinse and repeat.

This answers a question I’ve had for a long time: how can the telescope station-keep without any thrusters pointing “up”, away from the sun? Answer: very, very carefully.

> How long will it be breaking? (If at all, or of it is not already doing it).

All* of it's acceleration was given by the rocket at launch, it has been constantly "braking" since then as it's being pulled by earth's gravity, and it will reach L2 at same time it reaches a speed of 0.

* Not actually all in truth, since for margin of safety reason, the Ariane rocket purposefully imparted a lower than necessary speed, and the more precise thrusters on the JWST will be used to top it off with 3 different short burns (2 of which already happened), always staying just short of the required speed. The idea being that you want to make sure to be always missing a little bit of speed and readjust as needed, but never too much, as that is not recoverable, and the telescope would just drift away for ever.

No mention of ESA again, looks like it is solely NASA project, which it is not.

Shame.

I was under the impression that ESA's role was to get it into orbit, and is thus largely done. Is that wrong?

From Wikipedia:

> NIRSpec (Near InfraRed Spectrograph) will also perform spectroscopy over the same wavelength range. It was built by the European Space Agency at ESTEC in Noordwijk, Netherlands.

and more.

To be fair ESA contributed only with ~10% of total budget, and I guess much of that was the rocket.

I don’t see how that’s fair.

If that’s insignificant, why invite them? If that’s significant, why not mention them?

From the article, near the very top:

"A joint effort with the European Space Agency (ESA) and Canadian Space Agency, the Webb mission will explore every phase of cosmic history – from within our solar system to the most distant observable galaxies in the early universe."

They changed the link. It pointed to a tweet initially.

For those not up on the project, what are some of the earliest novel types of information we expect to receive from it?

"Meet hot methane-breathing life forms in your neighborhood!"

"5pc from Coatesville, PA"

One of the more interesting things that we'll get is data about what's in the atmosphere of exoplanets

https://jwst.nasa.gov/content/science/origins.html

Note that the next 5 months or so will consist of mirror cooling and calibration, so nothing until summer.

This will only work for a handful of very nearby exoplanets, unfortunately.

hell I’d be excited for 1!

The planets around Alpha Centauri orbit a red dwarf. They are almost certainly tidally locked and lack any atmosphere. The more distant ones that might not be tidally locked are likely frozen like Pluto.

...but who knows.

This one was really interesting to me because this kind of observation didn't exist when JWST was being specced out. We didn't know there were that many exoplanets around that we'd want to look at.

Would you happen to know if they can make intermediate observations while this is in process e.g. observe a relatively nearby object before the telescope is fully cooled and aligned? I'm wondering if they would be able to prove out the optics early on - this is no slam dunk as the Hubble proved.

My knowledge is basically 0, but from what I understood the sensitivity of the sensor is so high, that anything above its operational temperature would overload it and basically make a 'white' image. Basically like having a kitchen scale and then trying to weight an elephant on it (and somehow not breaking the scale in the process).

Not really… these telescopes aren’t like snapping a photo, they take long exposures. The famous hubble deep field image was a 20+ day exposure time spread out over months (due to orbits, etc).

Trying to get an image out of it too early would just be a mess, it’s kind of an all or nothing affair. The sensor needs to be at the right temperature and the mirrors need to be precisely aligned. It’s all built to be outrageously sensitive so it can operate at the level it’s meant to.

Also, each image it’s scheduled to take has been submitted years in advance.

Huge. This is the first large telescope observing in far infrared. Some things:

- very early galaxies (so far that they are redshifted to far IR). Hence the “looking into the start of the Universe” talk). We know they are there, and that they are unusual and super-interesting, but just can’t see them.

I think this is high on the agenda so I’m guessing some PR shots of ancient galaxies are due.

- cold objects nearby; brown dwarves, rogue planets etc. Maybe planets around nearby stars.

- I haven’t seen this discussed, but maybe: Kuiper Belt objects, maybe looking for Planet X etc.

Even earlier than galaxies, we'll be able to see some of the first stars that existed before galaxies formed.

IIRC the telescope will be able to see "back" into 98% of the observable universe.

Yup! If the universe's age were a single year, we're looking back to January 6th. Truly remarkable. :)

what prevents us from seeing back any further?

Redshift and mirror diameter. There is very little old light, so to see further, you have to collect more light to have a chance of catching those ancient photons. Also, due to expansion of space, the older the photon, the less energy it has, so you have to look deeper and deeper into infrared.

Disclaimer: not a cosmologist. We can see back further with other instruments, just there's less to see.

The universe's history: https://en.wikipedia.org/wiki/Chronology_of_the_universe#/me...

- We can see the cosmic microwave background (CMB), the earliest photons after the big bang still observable. This is ~14 minutes into Jan 1 if the whole age of the universe is a year. Satellites like the WMAP have done a great job of that.

- The dark ages that follow had few photon sources.

- JWST will be observing the earliest stars following that era.

There's a proposed radio telescope (that would have to be on the far side of the moon!) to observe neutral hydrogen photon emissions from the dark ages: https://en.wikipedia.org/wiki/Dark_Ages_Radio_Explorer

There were maybe 100 million years after the big bang with no star formation. Darkness. Here's a page about that era as it relates to Webb: https://webb.nasa.gov/content/science/firstLight.html

> what prevents us from seeing back any further?

The other comment mentioning darkness is wrong.

In the very early universe, it was extremely bright and hot. It was only after 100,000 years or so the universe cooled down enough to become transparent.

I'm excited to see what we learn about the earliest days of the universe since it can observe highly red-shifted objects.

It will take another 6 months before JWST will go into operation it seems. This page has a list of approved programs.

https://www.stsci.edu/jwst/science-execution/approved-progra...

Apparently it takes about 100 days for the instruments to cool down far enough.

https://planet4589.org/space/misc/webb/time.html

“Images of the first galaxies, the first black holes” iirc from Smarter Everyday’s interview with John Mather, sorry don’t have a time code for you

https://youtu.be/4P8fKd0IVOs

Word on corners of the interwebz has it that this is gonna prove the existence of aliens (or at least gov. are gonna frame JW as the indicator of alien life)

It could find a candidate biosphere. If we see a lot of free oxygen or other super reactive things like fluorine that would be very suggestive. It’s not proof but we don’t know many other processes that can maintain a high percentage of oxidizers in an atmosphere.

If we saw that the next step would probably be a telescope designed specifically to observe that target. There are some thoughts about using a telescope out near Pluto that could use the sun as a gigantic gravitational lens to photograph an exoplanet and get very detailed spectroscopic information.

If we have a planet nine that is a primordial black hole that would be an absolute killer gravitational lens.

Being able to see how galaxies evolved - you can see a galaxy 200M light years after the Big Bang and compare it to Hubble’s 500M years after the Big Bang.

Also spectra will be available to understand physical and chemical compositions at early times.

The full list of the first set of scientific missions is available here: https://www.stsci.edu/jwst/science-execution/approved-progra...

The overall idea is that JWST can see very faint objects in the infrared spectrum. The analogy I've heard is that it could pick out a bedroom nightlight on the moon from earth.

This feels perhaps like a silly comment, but I have this intuition that the data collected by JWST could prove to be some of the most important ever collected.

I keep telling people that, no matter what, we're going to learn something cool about the universe. I'm so excited to see these images. I mean, imagine humans 10,000 years ago, just surviving, maybe figuring out agriculture, and thinking about their place in the world. They looked up at the stars in wonder. Now, we've progressed to the point where we can polish gold down to the nanometer, and we're sending a giant hunk of origami circuits out to L2 to squint back to nearly the beginning of time as part of our eternal quest for answers.

Your comment is not silly.

I suppose I meant it felt silly in the sense that it would probably come across as seeming vague. And I may as well say a few more words. If I had anything specific in mind, it was the possibility that the JWST could find evidence of compounds in the atmospheres of distant planets that made it seem likely that there is life on those planets. Even if that doesn't happen, the fact that it feels like it's even on the table is amazing.

I'm also thinking back to when the Hubble came online and they started releasing the deep field images. And there was this moment where we all realized, "Wow, those things up in the sky that we all casually assumed were stars...many of them are actually galaxies. And all those black spaces in between are full of...more galaxies." Maybe astronomers already knew this; I don't know. But the average person didn't and it was hard to deny once we started seeing those images.

Not sure if it's justified, but I expect similar kinds of moments when the JWST starts collecting its first images.

People (including me!) really don't have a feel for just how far some of these instruments push things.

The Hubble Deep Field was a surprise to quite a few established astronomers. LIGO is measuring things way smaller than nucleons. The JWST can see so far back in time hat you can measure deltas from the beginning of the visible universe.

I know that I just don't have an appreciation for just how hard these things are to do.

In a comment above someone said it "might be high enough to image [...] alien megastructures if they exist"[0] and that was a clear sign I had absolutely no idea how powerful this thing was. I guess I was just expecting Deep Field but like... again? I don't know.

[0] https://www.popularmechanics.com/space/telescopes/a19346/jam...

Since 90% of the cost is probably in R+D of the telescope, one could build and deploy another for another 10%. Why isn't this done? Why is every space telescope completely unique?

Why would we need two? I would think the next one 20+ years from now would hopefully be exponentially better.

So that more researchers have access. Afaik access is shared and researchers have to make a proposal and get it approved before use, which to me suggests some kind of queue

Queueing researchers should be fine given the universe will be around for a while.

Next time you have to wait for your code to compile we'll say "should be fine, computers will be around for a while".

Redundancy would be good reason.

To get twice the science done, of course.

In 10 years we can send a bigger, simpler, cheaper, one-piece, non-foldable telescope in Starship for a fraction of the cost. The biggest saving wouldn't even be the launch costs - it would be the simple design allowed by relaxing the volume and mass constraints.

If only most of the cost was folding it (and if only Elon Musk's solutions somehow changed all the problems to fit them).

When it takes so long to build, it’s already obsolete by the time it gets launched.

If you made a new one every year, it wouldn’t be so bad of course, but a decade+? Oof.

It was so bad they kept redesigning it mid way through to upgrade things as new discoveries were made, which caused even more delays.

> redesigning it mid way through

And that doesn't have to be redone when making a copy.

Except it will because no one wants an exact copy, because if you do it at the same time that’s twice the rework, and if you do it later, you’re building something you know is obsolete. No one can resist throwing in some upgrades.

I believe in this case it's not 90%.

Much of the cost here was (on the ground) assembly and testing, given the intricate nature of the setup.

What about all the costs in developing the test procedures? Obtaining the test equipment. Designing and building the test rigs. Designing, coding, and debugging the test software. Training people on how to do the tests. Endless committee meetings on if the tests are accurate and complete. Failure analysis. I bet they're enormous.

Running the same tests again on another part would be at very little incremental cost.

Part of the reason is that each telescope has different scientific goals. For example, Hubble is a visible wavelength telescope and we learned a lot from the data it collected and continues to collect. JWST is an infrared telescope designed to see wavelengths that Hubble cannot see, and has a different set of science goals.

I don't think that's necessarily the case. For advanced R&D projects like this, it's super difficult to capture all the processes and knowledge the first time around required to build it a second time. I think it would probably be cheaper and faster, but not by such a large amount. Also, given the timeframe of this project, I would estimate that many of the parts may be difficult to obtain again.

There's also the fact that for projects like this, so much is learned along the way that you probably wouldn't even want to build it the same way again, having found better, more efficient, cheaper, etc. ways of doing things.

I was wondering that myself. How much would a second Webb cost? Or three? Or a fleet of smaller ones.

I’m assuming all of this was looked at, just curious what the answers to these questions.

Kudos to the team! Huge accomplishment.

My guesses:

- due to the time between the start of the project and the end, enough time has passed where there are sufficiently new advances in science/tech/robotics/etc to open up new possibilities

- a second one will probably still cost >10% of the original

- a second one wont yield enough benefit to be worth it

like...the JWST isn't anything like hubble, and can do things that hubble cannot. So it's not like a fleet of hubbles would equal one JWST or something.

Because it's a wrong assumption. Significant cost come from the assembly and testing of all the components itself, that you would have to redo entirely.

Also if you were to build just 2 or 3 of them, you can't expect any economy of scale.

On top of that, the operational cost of JWST is expected to be around 1B$ for it's lifetime, you could expect that to be similar for every single replica you have.

And finally, you can only put one per rocket, and just the rocket is about 200M$ dollar, and you need to add all the cost of shipping the telescope to Guyana, that's not cheap.

So overall, while a second replica would not cost you another 10B, it would probably cost in the order of 3-5B$, that's a lot of billions for a telescope with exactly identical capabilities to another one. It would still be useful, as astronomers are going to have to compete for time on the JWST and not everyone will be served, but the benefits of a second one would be marginal compared to the benefits of the first one. So the price/benefit ratio might actually be worse on a new copy.

Meanwhile, there is a myriad of other very cool NASA projects that would greatly benefit from 3-5B$ instead and do things that we haven't done so far.

This question comes up in every one of these threads and this is the correct response.

If you look at the line items on a build, you might see something like a $200 bolt. It’s not that there was $198 of R&D going into the design of the bolt, it’s that quality management drives the cost. Chain-of-custody, bonding, material testing, witnessing etc. are all part of that effort and they don’t scale like a design spec does.

If it's a one-off bolt with a custom design, it will likely cost thousands of dollars.

The GPs point was that subsequent builds would make it no longer a one-off design. My point is that there are other substantial cost drivers that break their assumptions. My analogy of a $200 bolt was not meant for a custom design, but the point stands regardless.

(I’ve worked in a custom machine shop for aerospace, and depending on the tolerances, the actual build is typically not thousands until you factor in all the aspects in my previous post)

Assuming your figures are correct, you'll get double the data for another 30% cost.

If you wait a month before launching #2, if problems appear in #1 (like the telescope mirror was ground improperly) it can be fixed in #2.

The operational cost will not double. The same ground facility, equipment, and staff can manage both.

If you're buying two identical launches, you can get a quantity discount.

> the benefits of a second one would be marginal compared to the benefits of the first one

And yet I read many glowing accounts about how much extra value came from extending the Hubble's lifetime.

I do have some experience with this. I worked for 3 years on the design of the 757. Thousands of engineers spending maybe 5 years on it. None of that has to be repeated. In a machine shop, most of the cost is in the setup. Making two adds little cost. I had a job assembling electronics to help pay for college. The first board would take 2 hours to build. The next one, half that. The fourth, 20 minutes.

I'm sure there's plenty of software on board that machine. On HN we all know how expensive making software is. Making a copy costs nothing.

Agree. A replica wouldn’t have to be sent to L2 for that matter. Pretty sure a lot of science could be done with even a slow trajectory leaving the solar system, if orbiting something else is infeasible.

As I understood the engineering of the JWST requires it to be at L2 so it's in permanent shadow of the sun and can keep the very low temperatures necessary for good infrared image quality.

It has solar panels, so it can't be in shadow. IIUC the advantage of earth-sun L2 is it's away from the light and shadow of the earth and moon, while being reachable by radio year round.

I didn't check for sources again earlier, but this NASA article [1] explains it.

Yea shadow was the wrong word and doesn't actually apply because of the relative size of the sun and earth. However the L2 point is by definition in a straight line Sun -> Earth -> L2, so if the sun would be a single point light source that would block the sun and place the JWST in the permanent shadow thrown by the earth. The point is actually that the sunscreen is always facing earth and sun at the same time to block/reflect a maximum of heat.

[1] https://jwst.nasa.gov/content/about/orbit.html

It's orbiting L2, not at it. It will have basically constant sunshine, which is good - solar panels provide all its power. (no RTG)

It has constant sunshine on one side, and constant darkness on the other.

> double the data

Yes, but the data has diminishing returns as well.

The real value in a second unit is having a backup in the event of a total failure of the first. But that's a hard sell to the taxpayers who fund these things.

> Yes, but the data has diminishing returns as well.

I find that hard to believe considering there's literally a universe of things to look at. We find surprising things everywhere we look.

$3-5B would go a long way to a new Einstein telescope (ie. gravitational waves detector). It would likey allow for significant sensitivity increases in the existing ones. It could propel the National Ignition Facility or ITER forward. It could be used to build a new Arecibo. It could add an enormous amount of low-frequency telescopes - or other scopes for very large integrated scope arrays.

I'd much rather broaden our view than double it in one narrow band. (Or advance fusion research.)

For reference, the entire NSF budget is about $8B (maaaybe $10B next year!).

That's not true. The potential for surprises gets smaller and smaller the more data you collect. The Webb will produce surprises at first because it is able to make new kinds of observations that were not possible before, but after a while that new data will be used to improve our models and subsequent observations in the same regime will (almost certainly) be less surprising as a result.

> The potential for surprises gets smaller and smaller the more data you collect.

Mathematically, you are quite correct.

But do you really believe that with one little ole' telescope pointed at the freakin' universe you're going to reach a significant point of diminishing returns?

It's like saying if you invent the first microscope, and discover bacteria, why bother with another one?

You might see more new things if you spend the next US$4 billion on a different instrument instead of a carbon-copy Lagrange-point infrared telescope. But you're right that you also might not.

I wonder what the optimal number of James Webb space telescopes would be? The cost per unit as a function of number built has been debated, but what about the marginal utility (benefit) ? If you built two instead of one, you would get lots of benefit from the second - an entirely independent set of scientists could decide what to do with it, and maybe explore entirely different subjects. If you made ten thousand of them though, the last one would be nearly useless, because there aren’t enough smart people to make proper use of it. My guess is that after a couple of them, the marginal utility falls off very quickly.

> It's like saying if you invent the first microscope, and discover bacteria, why bother with another one?

Exactly, why bother with discovering millions of bacterias with 20 copies of the same microscope if for the same cost can build 5 different microscopes allowing discoveries of thousands of fungi, viruses, protozoans, algae, plankton etc.

In astronomy there are multiple bands to observe - gamma rays, x-rays, EUV, UV, visible light, near-IR, far-IR, short/medium/long radio waves. There are also gravitational wave observatories and special instruments like spectrographs and coronagraphs for imaging exoplanets. Every of those observations needs highly specialised instrument but brings a lot of new insight about what is happening in the universe.

Most of Hubble's groundbreaking discoveries came in first 10 years of its operation. Less in next 10 years. Even less in third decade. In fact its final service mission had been cancelled once but was reinstated once it was clear that JWST will be massively delayed and risky. For combined cost of Compton (gamma/high x-rays), Chandra (low x-rays) and Spitzer (infrared) we most likely could have built and launched another Hubble, but there was no point as those 3 generated much more valuable science than another Hubble ever would.

> But do you really believe that with one little ole' telescope pointed at the freakin' universe you're going to reach a significant point of diminishing returns?

I believe that James Webb has some unique capabilities, and a whole lot of overlap with other instruments, too. For things that you can only do in infrared, we have Herschel's history of observations, and VISTA. Sure, JWST is bigger and up at L2, and will be better overall, but VISTA's instruments have some advantages.

Not to mention all the other telescopes and ways we have of studying the universe.

There's all kinds of other things the government has spent $3B on in the intervening development time that I'd trade for another JWST. But it's a bit moot, here: NASA didn't have another $3B to spend. If you made JWST $3B more expensive, you'd not get 2 telescopes instead of 1: you'd get 0, because JWST almost died because of cost overruns.

(And even if NASA had $3B more--- there's a lot of other things that might have been better to do with it than JWSTx2).

It's not quite the same thing, but as an analogy: should we have built two CERNs (edit: LHCs, not CERNs) to "find" the Higgs boson faster? Or was it better just to build one, expecting that it had a good chance of finding the particle and other new physics, and then put future funding toward different/more advanced and capable instruments that will give us a window into even higher energies/entirely new observation spaces, rather than just accelerating our search of the same spaces by low integer multiples?

My understanding is that the JWST opens up new observation spaces, specifically very distant and highly redshifted objects that Hubble couldn't capture. So we should have a lot of data on a new class of objects in fairly short order, and thanks to the cosmological principle we can expect to see similar distributions of the same objects and phenomena no matter what direction we look in. As we gather more data, we will converge on an understanding of these new spaces, and eventually the error bars will shrink to the point where further observation is generally not giving us much new information.

Is it better to build more JWSTs, to accelerate that convergence by low integer multiples and similarly increase the chance that we'll happen to point one at something truly new and "surprising"? Or should we spend our money on bigger and more capable instruments that we know will give us access to entirely new observation spaces that are completely out of reach of the JWST and other extant instruments?

I don't think it would be such an obvious question, if we weren't constantly getting better and better at designing and launching large and complex instruments. As things stand, we can let JWST and its ilk blaze the trail, then follow up with cheaper instruments building on lessons learned and our general technological and economic progress.

It's not quite the same thing, but as an analogy: should we have built two LHCs to "find" the Higgs boson faster?

Depends. Is experimental time at the LHC anywhere near as competitively-rationed as it is for a space telescope like Hubble or Webb?

I don't think Hubble or the JWST have much to do with the question of whether we should have built another LHC to collect data twice as fast, except as an imperfect analogy to help frame the question in casual consideration—i.e. the reverse of the analogy I made in my comment.

In fact, answering that question should come down to whether we expect the LHC to realize the majority of important observations "in range" of its instruments within its projected lifetime, and also in time to make useful contributions to the selection and design of future experiments.

To answer your question directly: yes, AFAIK the LHC is fully utilized; when it's not running, it's down for maintenance or upgrades, and its observations are (or have been, in its active periods) in high demand. But it's far from clear that building another one would yield a good return on investment, especially given the opportunity cost of diverting funding from future experiments.

Double the data may not be worth 30-50% more money to NASA. Going from no data of type X to 1 data of type X is worth a lot more than going from 1 to 2, and so the leap from 1 to 2 might just not be worth it, even if it is 50% cheaper than the leap from 0 to 1.

>you'll get double the data for another 30% cost.

Sending just another similar telescope that provides more same typed data (wavelength, angular resolution) is probably not worth it. Spending the same sum for different type of telescope would be better use of the money.

Hubble, Hershel and Webb were are made for different wavelengths, they are complementary.

The Extremely Large Telescope (ELT) is ready around 2027 and it will be the next revolution. 0.005 arc-seconds compared to 0.1 arc-seconds of JWST. (978 m2 vs 25.4 m2 collecting area)

>Making two adds little cost.

I think you are overextending your experience in a production environment here.

I’ve worked in both, and the type of builds in these aerospace applications still have huge costs in subsequent runs. Hell, even rebuilding an existing component can be prohibitively expensive.

Much of the GSE was likely existing so that’s probably a non-issue.

> huge costs in subsequent runs

Often that's because they have to rebuild and reset the tooling. Within the run, though, the incremental cost should be minimal.

The huge costs may be huge, but not huge compared to the cost of the prototype.

IMO your logic fits with large production runs.

In space applications costs can be exaggerated compared to actual production environments because the risks aren’t mitigated by something like the FAA, meaning they are often mitigated by some downstream process. Besides, a lot of the the designs already include critical spares, so there’s more than a single run, even in a one-off design

So build a copy out of the spares! If they're there, they're already paid for.

Not every part meets the criteria to be a "critical" spare. You don't have a complete set of spares for every component.

Are you suggesting that spares are only produced for the cheap parts?

No. Only for the parts deemed critical.

An example may be a part with a long lead time and no redundancy. If it is found defective during testing, they need a replacement right away and don’t want the schedule to slip while it gets fabricated

A lot of times when you make one of something, there's stuff you would make tooling for if you were going to do more than one, but which instead you do by hand. Sometimes this is even true in software, but not very often, because the advantages of being able to recompile something from source code are so huge.

Even when doing things by hand, making a duplicate alongside the original is not much more time. That happens to me every time I do something by hand.

I think the error in your assumption comes, in part, that there’s is tooling set u for mass production of each part.

A lot of parts are hand-fabricated. The setup may take time but it’s not necessarily like a assembly plant that requires new dies on each design.

This is true for things like motor mounts and pipe flanges, but not for things like optical surfaces and lathe ways. Even in cases where it is true, if you didn't make the duplicate alongside the original, you have to do the setup again to make a duplicate.

Yes, make it alongside the original. I've been saying that all along.

Doesn't help with telescope mirrors, as you likely know from experience.

I think your mindset is stuck in thinking about this as an airplane production environment because that was your experience. And your points make sense in that type of environment. But research aerospace in which JWST operates is a very different scale, operating much more at the margins where the tech is less well understood and takes much longer to develop. Investing billions for redundancy on an unproven system is a big risk (besides the fact that it would likely be designed differently - and better - if started today).

The sunk cost fallacy already drives a lot of these projects...imagine how much worse it would be (and how many other, competing projects wouldn't get funded) if the costs were higher.

I think it's more that this argument can be continued ad infinitum. Yes the JWST had significant cost overruns, but in the design phase these types of projects necessarily are looked at as how to best utilize a fixed size grant of money. At the end of the day the decision got made to make a better single telescope than to make two simpler telescopes.

I wouldn't be surprised though if we start to see clever design proposals coming down the pipeline, like several cheaper telescopes, swarm designs for giant radio telescope arrays, and even amateur designed and operated space telescopes. Remember that the JWST started it's design phase back in 1996, and the economics of space launches have changed considerably since then.

I remember having manuals printed in the 1980s. The first manual cost $1000 to print, the second one $1. This was with camera-ready copy. Never mind all the cost of writing the manual, proofing it, and formatting it.

When I worked at Boeing, the first forging of a part cost $250,000. The next, just a handful of dollars.

At Boeing, the first airplane gets a ton of testing, as the design is being tested. Airplanes #2 and on only get tested to verify it was built according to the design, at a tiny fraction of the cost of testing #1.

You still don't choose forging as a process to make quantity 2 (unless you absolutely need forged parts for strength). Instead, you're milling two parts from billet.

Milling 2 parts from billet is cheaper per unit than milling 1 (some shared setup and programming costs), but it's the same amount of raw material and basically the same amount of operator time.

You're right that a one-off forging is so expensive that a hogout will be used instead. My point was how expensive one-offs can be compared to multiple ones, and I used extreme examples as illustrative.

Even in custom machine work, the cost is in the setup. A machinist can make two identical cuts on two parts for not much more cost than one cut on one part.

Doubling the data will also double the processing requirements for that data. The observatory is just the remote part of this operation. The data doesn't do squat unless stored, analyzed and interpreted by expensive professionals on expensive equipment.

It's like saying if you're gonna build a chip fab, why not build two while you're at it? Well because the building isn't the operation.

Why do I have to do all the thinking?

1. Grad students and computers are cheap.

2. Crowd source it. Make the data (and the programs that process it) freely available. Let anyone who wants to analyze it - if they find something cool, they can be famous. They'll do it for free.

3. Processing doesn't have to be done in real time. There's no problem with taking 5 years to analyze 1 year of data.

All of the above are already utilized, to varying degrees of success, and lack thereof. I believe in this stuff but let's be real, we're exploding fossil fuel to propel a camera into space. Baby steps for global consciousness.

> Assuming your figures are correct, you'll get double the data for another 30% cost.

I think 30% is probably a reasonable guess, based on past programs where people have flown 2. You get to reuse design and some fixturing. You get to share some operational costs. But you're not at unit counts where you benefit from mass production techniques and a whole lot of verification and qualification work are still effectively one-offs for each one.

(You save a whole bunch of costs related to making a repeatable program that can turn out hundreds of an item, but more has to be validated/verified for each unit).

The thing is-- what's the marginal value of the additional data (and of the higher priority data arriving earlier)? Would you rather have 2 James Webbs for $13B, or 1 James Webb & some other $3B mission?

(Or, at the outset/original decision making: do you aim for 2 somewhat simpler telescopes or 1 really awesome telescope with the block of money you're given?)

Another poster here remarked that spares would be made. That would indicate the cost of doing so isn't that remarkable.

Lots of engineering models. Some spare parts for parts of assemblies.

Not a lot of complete, flight-capable assemblies.

I'm actually teaching a bunch of high school students to make a cubesat right now, and we are going through costing of:

* Prototypes -> protoflight -> flight, no engineering model

* "Flatsat" electronic engineering model, prototypes -> protoflight -> flight

* Prototypes -> qualification article -> flight article, + "flatsat"

* Prototypes -> qualification article -> flight article + ground engineering model

There's a whole lot of derisk that happens as you go down that list, but the cost and labor increase (the latter is "free" for us but also limited) is substantial.

>I do have some experience with this. I worked for 3 years on the design of the 757. Thousands of engineers spending maybe 5 years on it.

Just wanted to say that's really awesome. The 757 is by far my favorite Boeing jet of all time. They are so overpowered it feels like taking off in a fighter jet. Delta still flies them from LAX to HNL, and it's always so much better than cramming into a 737.

I am always pleased to be boarding a 757! I was sad when the front page of the Seattle Times showed one being cut up for scrap.

> Assuming your figures are correct, you'll get double the data for another 30% cost.

The debate over the cost to build another is largely moot. You'd struggle to find the people to do it for many reasons. The talent is even scarcer than the money.

> the benefits of a second one would be marginal compared to the benefits of the first one.

This can't be true.

The benefit of the JWST is the observations it can make Two JWSTs can make twice as many observations as one, so it provides twice the benefit.

In some sense there is a diminishing return in that the most important observations will be attempted first, and and over time the average observation will be less and less important. But surely there is many decades of pent up very important research!

JWST was built to see in IR to help us get answers to a set of important questions. The best known one being trying to elucidate the question around the rate of expansion of the universe. We hope to get some answer by looking at objects much further away in space and time with the JWST and getting new estimates for the expansion rate. Something we cannot do today.

You don't need two telescopes to do that, you just need one with a specific set of IR capabilities.

Sure, having twice the imaging power is better, but it's definitely far from doubling the benefits. The lifetime of the JWST is expected to be 10+ years, that's a lot of data that will come to us already, and everything the astronomer community deems important will have time on the telescope.

Just like we only needed 1 LHC to confirm the existence of the Higgs boson and the robustness of the standard model. Building two of those would have been a massive waste of money, it was much better to build one, run experiments, assess the results and then use the money that was saved by building a single one to build new tools with new capabilities to answer the new questions.

Of course the reality of government budgeting is a little bit more complicated than my rosy picture but the point stands.

A small nitpick: yes, we only needed 1 LHC to confirm the existence of the Higgs boson, BUT we made sure to have two experiments (ATLAS and CMS) looking for it. As far as I know, every modern high energy physics accelerator has had two (or more) sister experiments to cross-check each others!

Of course, it is not a perfect analogy, since the two experiments are not replicas. They try to address the same physics cases, but they were designed, built and are operated in a completely independent way.

JWST is a general purpose telescope, and the by far most powerful ever built.

It should, if working as intended, be able to observe anything in the sky, and get the most detailed pictures ever seen of them. In wavelengths not seen before.

Without doing the math, there are probably billions of interesting things to point it at, most of which it will never get around to.

> be able to observe anything in the sky, and get the most detailed pictures ever seen of them

That's just not true. JWST is primarily infrared, with some limited ability to observe in visible light (essentially half of the spectrum, no blue or green). It has no capability in ultraviolet, x-rays, gamma-rays, microwaves or radio.

You just can't build a single instrument to "observe anything".

JWST can't do what Hubble can for the most part, and Hubble can't do what JWST will do.

WMAP, Spektr (Russian), Chandra and many other missions all do different things and help us answer different questions with very little overlap.

You seem to argue against something I didn't say.

I understand it observes a different frequency range than Hubble, but it can still "observe anything in the sky, and get the most detailed pictures ever seen of them".

> but it can still "observe anything in the sky, and get the most detailed pictures ever seen of them".

That's my point: it cannot!

Not all objects are visible at all wavelengths. Some extremely old and far-away objects are not emitting anything in the shortest wavelengths because of red-shifting, and you need infrared capabilities to see them (hence JWST).

Dust clouds are also blocking certain frequencies of light from reaching us, so you need instrument detecting certain frequencies to see through them. But if you want to study dust clouds, well you obviously need a different instrument that will not see through them.

If you care about observing very energetic objects like neutron star, you need x-ray capabilities.

If you care about studying atmosphere of exoplanet your best bet is UV light, and this is why NASA is working on LUVOIR.

It's like saying you can observe anything with an iPhone camera. You can't, if you care about imaging a brain tumor or a broken bone, you need x-ray, your iPhone just won't see through the skin. And if you care about taking a picture of the skin, you can't do that in x-ray.

Are you seriously suggesting there is no other value in infrared light images? That there's only one thing worth looking at in infrared? That nothing else one points it at could possibly yield a surprise?

I'm astonished. I don't think we remotely know enough about the universe to draw such conclusions.

> Are you seriously suggesting there is no other value in infrared light images

I have never suggested that no. What I am suggesting, is that if you asked the astronomy community wether they want to spend 3-5B$ into getting an exact copy of the JWST, or spend those 3-5B$ into a different telescope, with capabilities complimentary with the JWST, you would get an absolute overwhelming majority voting for the latter.

We are still going to invest in future IR telescopes, but they won't be exact copy of JWST, they will either be complementary (see the future Roman space telescope) or will just be based on newer technologies and be more powerful.

There is simply little value in getting twice the same instrument for that price tag.

Why didn't we build another Hubble? The US build 18 of those for reconnaissance purpose but a single one for astronomy. Because the astronomy community never chose to spend their budget on that, instead they chose 4 new telescopes, with 4 different capabilities, all different from Hubble. That's where JWST comes from. They could have asked for 4 JWSTs instead, but they didn't because that would be terribly pointless.

> > but it can still "observe anything in the sky, and get the most detailed pictures ever seen of them".

> That's my point: it cannot! > > Not all objects are visible at all wavelengths.

A JWST observation showing nothing is new science. Now we know that object emits no light at those wavelengths even when observed by the most sensitive instrument!

But of course those are exceptions. Most things we point JWST to will be seen in greater detail than ever before, and also in frequencies not seen before.

> If you care about observing very energetic objects like neutron star, you need x-ray capabilities. > > If you care about studying atmosphere of exoplanet your best bet is UV light, and this is why NASA is working on LUVOIR.

This feels like deliberate misunderstandings (conscious or not) of my points. I don't think we can get any further in this discussion.

There is a list of specific questions JWST was built to answer.

* What were the first stars and galaxies like?

* How do stars come to form deep within a dusty nebula?

* What are the atmospheres of Earth-sized worlds like, and do they contain signatures of life?

* How far away do we need to look to see the pristine, pre-stellar Universe?

* How did the early stars and galaxies assemble to give rise to what we have today?

Once these questions have been answered, answering them again with exact copies of the same instruments at the same fidelity does offer diminishing returns. Sure it will provide valuable data for its whole lifespan, but there are diminishing returns. Better to invest the marginal cost of another JWST in a different instrument that gives us measurements the JWST can’t. There will be successors to the JWST, and that’s where the investment should go.

I know NASA has a reputation for bureaucracy, but I don't think it will be forbidden to use JWST for other purposes than those 5 questions?

It is capable of being aimed at any point of the sky and show us things we've never seen before, is it not?

Reminds me of when Seattle finished boring a transit line with their zillion dollar tunnel boring machine, they cut it up and sold it for scrap. Never mind that the machine could have just kept right on boring, extending the line.

That is true, but it was designed specifically to perform certain tasks. It’s capable of much more, but those are essentially bonus stretch goals. Nobody is saying a second JWST would have no value, or couldn’t do useful science, that’s a gross mischaracterisation. There are diminishing returns, that’s all.

We all want more science, the question is what’s the best use of 3-4 Bn in extra funds. The real question is which other future telescopes and space missions would you cancel to get a second JWST?

Honestly that doesn't sound like much money. Especially since these projects aren't solely funded by one country, even if one foots most of the bill. Also, $1bn over it's lifetime is really cheap even just for the US alone.

> Honestly that doesn't sound like much money

Well by comparison, here is the cost of two of the most impactful recent-ish (post 2000) space telescopes the US has launched:

- Spitzer: 700M$, JWST being it's successor. This telescope allowed us to detect an exoplanet through light for the first time, refine our understanding of the shape of the milky way, find candidate objects to be further observed by JWST and many more contributions.

- Kepler: 600M$, this is the telescope that allowed us to understand that planets were not rare at all, detecting more than 2500.

So imagine what you can do with 3 to 5B$. Certainly more interesting things than just doubling your data gathering rate of a single telescope.

Instead of comparing to other telescope projects maybe better to compare to other mega science projects. Or better yet, other government costs. Though of course we'd need to run a cost benefit analysis.

The thing is that these numbers are big for us and most companies, but these are government numbers and decades of work. Both factors are important. It's $11bn over 24 years, or 458m/yr. I'm happy to pay an extra $3/yr for this project.

> I'm happy to pay an extra $3/yr for this project.

Yes, I think many of us would be happy to. But the reality is that NASA has to fight a pretty ferocious budget battle every year, and often (not always) delay and increase in JWST cost has meant postponing or cancelling other missions.

For example the Nancy Grace Roman Space Telescope, which was deemed the top priority by the decadal survey in 2010 almost got canceled in 2018/2020 because of JWST overruns.

This Nature article is a good read: "The telescope that ate astronomy" [1] (and at the time of the article, JWST cost was "only" at 5B$).

I am very excited about what we will observe with the JWST, but shelling yet a few other billion of dollars out of NASA's tight astronomy budget to get an identical copy, mean we are yet again cancelling or postponing other exciting missions that could help us answer very important questions.

[1]: https://www.nature.com/articles/4671028a

This isn't so much a limited resource problem as an allocation problem. If US, and western, interest increases in science then funding more missions like these will be more popular and Congress will increase budgets. But budget allocations are low because they are unpopular. We talk about the high costs of these missions but they are close to rounding errors in the US yearly budget. It's weird to me that we argue over pennies when we're spending hundreds with no question. We'd say that's insane if we were trying to set budgets for ourselves. The reason it works it because the total numbers are large and we aren't scaling properly. It's a distraction.

If it makes you feel any better, if I had Gates' money I'd be funding a fleet of probes. Most of the same design :-)

Perhaps the cost of NASA probes is so high because politically they cannot tolerate failure. This drives the cost up 10x, which means it's a self-fulfilling prophecy that failure is career-ending.

Contrast this with Musk's approach to blow them up until they work, and then he has cheap launch vehicles.

I remember a NOVA on one of the Mars landers. Nobody had ever landed anything on Mars with a parachute before, so the developers had a massive problem. They built this humongous facility to test parachutes. One design after another failed, for several months. They finally found a design that worked.

I don't know what building a second chute would cost, but I bet it would be less than one thousandth of the cost of #1.

The Hubble telescope wasn't unique. It was simply the first one that was pointed away from earth.

For the JWST, is there even room for a 2nd telescope at L2?

There's room for a lot of them, it will be in orbit around L2, not exactly in L2.

Space is huge.

But L2 is just one point

That's an abstraction. In reality, what we call "L2" is an orbit around the L2 point. No shortage of room.

I was thinking since the point is so unstable, the orbit must be extremely small...

Boy was I wrong. The orbit is about the same size as the moon makes around the earth. [0] Its HUGE. We would run out of material to make satellites before we ever ran out of room.

[0] https://jwst.nasa.gov/content/about/orbit.html

Why spend money on JWST 2 when you could as well spend it on ... LUVOIR? ^^

https://en.wikipedia.org/wiki/Large_Ultraviolet_Optical_Infr...

taps temple Why go big when you can go gigantic.

JWST versus LUVOIR-A... just wow! Imagine difference in quality of pictures!

https://en.wikipedia.org/wiki/Large_Ultraviolet_Optical_Infr...

Actually LUVOIR will most likely have smaller 6 meter mirror to reduce cost and use lessons from JWST construction. It will be simpler design than JWST as it will use only 2 or 3 layer sunshield and no cryocooler (creating equipment that can work at 5 Kelvin was massive issue for JWST). Its main science goal will be examining atmospheres of exoplanets, plus general observations like Hubble.

It will observe in UV/visible/near-IR so its resolution will be higher than JWST's as shorter wavelengths are easier to focus (diffraction limit is a function of wavelength) but it will not be able to see objects at the very end of observable universe as it cannot image in mid-IR or longer wavelengths. There is still plenty of interesting stuff closer to us and it will be "true" successor to Hubble.

There are several space telescope projects under consideration besides luvoir.

Habitable Exoplanet Imaging Mission https://en.wikipedia.org/wiki/Habitable_Exoplanet_Imaging_Mi...

Lynx X-ray Observatory https://en.wikipedia.org/wiki/Lynx_X-ray_Observatory

Origins Space Telescope https://en.wikipedia.org/wiki/Origins_Space_Telescope

I know nothing specific about the JWST, but here is a theory:

NASA is a government agency, which makes what it does ultimately political.

In a political "economy", the return on investments is mainly PR. Politicians aim to get voter sympathy in return for investing $B in NASA.

And voters won't much care if you put up 3 JWSTs or 1.

> 90% of the cost is probably in R+D of the telescope

While I might have guessed that, IIRC someone at NASA said that most of the cost is parts, assembly, and testing of a massive, highly sensitive, highly unusual custom build. Many (most?) parts are custom made, and even finding vendors to make them again would be difficult - wasn't the manufacturing completed several years ago? Again, IIRC, they said a second one might even cost more.

Projects to widen freeways face a similar diminishing return. The most value arises from the new capability. Each lane thereafter does not yield linearly increasing returns.

Reminds me of the line in Contact: "why build one when you can have two at twice the price?"

Contact was written by a scientist who had no experience whatsoever in building things.

That doesn't sound right...

> Carl Sagan played a leading role in the American space program since its inception. He was a consultant and adviser to NASA beginning in the 1950s, he briefed the Apollo astronauts before their flights to the Moon, and was an experimenter on the Mariner, Viking, Voyager, and Galileo expeditions to the planets. He helped solve the mysteries of the high temperature of Venus (a massive greenhouse effect), the seasonal changes on Mars (windblown dust) and the reddish haze of Titan (complex organic molecules).

> For his work, Dr. Sagan received the NASA Medals for Exceptional Scientific Achievement and for Distinguished Public Service twice, as well as the NASA Apollo Achievement Award.

https://www.planetary.org/profiles/carl-sagan

I've met Sagan (he came by our dorm for conversation and dinner with the students). He was a great man. He was wonderful to talk to. He has made great contributions to science. He deserves all the credit and accolades you mentioned.

But I doubt he ever set foot in a machine shop. Making things is an entirely different skill.

Machine shop experience is not related project cost estimations.

Sorry, I'm not buying that. But that notion might be one reason why government projects cost so much.

I've taken apart cars many times. I know when I'm being fed a baloney sandwich when taking my car in for service, and use that to pare down the estimate sometimes as much as 50%.

(For all the women who rightly complain about being scammed by auto mechanics, I can vouch for them doing their best to scam me about 75% of the time.)

I'm not buying it either. NASA wasted billions on the space shuttle and single-use rockets until a programmer from Paypal showed them how to build re-usable rockets. Musk regularly refers to the economics of airliners as inspiration.

Obviously ideas to improve the economics of space exploration can come from anywhere, but one of the first places I'd look would be the Boeing machine shop.

And we haven't touched on human spaceflight, where economy must be balanced with safety. Hmm, I wonder what industry has the most experience with such engineering tradeoffs?

But who had experience with a twin space science probe project.

After reading / watching all the info on this page [1], I find it very hard to imagine even the tiniest reduction in cost in going from 19 insanely complex mirrors to 38, then there's all the insanely complex instruments. It might even be the case that the super specialised and expensive machines that were built to construct the telescope itself wouldn't be able to produce 2 full telescopes without being upgraded / refurbished, hence costing a lot more. Everything about this ambitious project is probably once-off for a very good reason.

[1] https://www.jwst.nasa.gov/content/observatory/ote/mirrors/in...

The technology is pretty outdated already at launch time. I think they take the lessons from this one into the next telescope.

There is also the question of the part if the spectrum they are looking at. The JWST is for infrared so I assume the next one will be for different frequencies.

I wish there were a FAQ. This comes up every single time there's a thread about Webb on HN. Search previous posts. You'll see a hundred answers to your question, some of them well researched.

This is accurate, and unfortunately the questioner is going through all the threads repeating naive objections to the legit answers offered by people familiar with aerospace. I know the guy who led the assembly of the JWST/MIRI cryocooler, which was one of a handful of high-risk items on the spacecraft, and all of his team’s time was taken up with assembly, build, integration, and test, not just abstract design. I’ve explained this kind of thing in past threads, but it’s tiresome!

After reading all these replies, I'm glad Musk never listened to people who said he couldn't make a cheap, reliable rocket that could land on its tail.

grump, grump, grump

Your point is completely unfair.

Sure if our goal was to mass manufacture a "cheap and reliable JWST" we could, with a lot of money, create an entire assembly line and benefit from economies of scale. And then what? What are we supposed to do with 100s of JWST? It's cool they only cost 200M$ each now, but we don't need them.

What we need after JWST is a different telescope with different technologies to answer questions that JWST cannot answer and to follow up on the discoveries from JWST.

SpaceX and Boeing are responding to a scale problem: getting as much mass as possible into space, getting as much people as possible from point A to B. You solve a scale problem with scale.

JWST is science instrument, looking for answer to specific questions, once those answer are found we will want a different instrument to answer different questions. Scale does not help. Multiple JWSTs cannot see what a single one can't.

Is it unfair?

In Spring 2020, in this forum, the vaccine experts here told me in no uncertain terms that a vaccine would take 18 months to develop. I said it could be done in 6 if all the slack was removed, and things done serially were done concurrently. I was told that was all completely unreasonable and impossible.

6 months later, the vaccine was released.

The JWST has what, 390 single points of failure, and cost $10B. I.e., it cannot afford to fail, so $10B was spent to ensure it would not fail. And it worked! But suppose for $1B one could build a less reliable JWST. They fail like Musk's early rockets, but since they're cheaper the failure is not career ending, and you can iterate the design fixing the things that broke rather than trying to make everything perfect. You wind up in the end spending a lot less money.

BTW, the airplane industry long ago gave up trying to make parts that could not fail. (390 parts that could fail and end the mission is pretty darn risky.) Instead, one makes redundant systems. It is far, far cheaper, and yet more reliable than going for perfection. Yes, it'll be heavier, and that will cost more. It makes airliners heavier, too, and it indeed costs more. But in the end it costs less, much less.

Do I know how to build satellite telescopes? Nope. But I do know how airliners are designed and built. And I know that Musk upended how rockets were designed and built.

As for different technology telescopes, I bet a lot of the telescope could be the same from design to design, just changing the instrument package.

> Yes, it'll be heavier, and that will cost more.

It won't just cost more, it'll be impossible. Aircraft care a lot about weight, spacecraft are obsessed with it, because it's often an absolute limit based on what launch technology you have available and where you're trying to get. JWST doesn't have any spare weight to try to build more redundancy.

> But suppose for $1B one could build a less reliable JWST

Well, the calculus of many single failure points makes this questionable. Even if you're 99% confident in each point of failure, with 390 failure points you have a 2% chance of success. You need extremely reliable components. Also, it's not clear that the majority of the budget is being spent on increasing that reliability: certainly a lot goes into testing, but all of that testing is generally a lot cheaper than a launch and rebuild.

What I am saying is unfair is your insistence on trying to think of astronomy as a problem that can be resolved by scale.

> that a vaccine would take 18 months to develop. I said it could be done in 6

Cool anecdote. I was also part of those who thought it would be done earlier, we agreed on this. This is not comparable at all.

> so $10B was spent to ensure it would not fail. And it worked! But suppose for $1B one could build a less reliable JWST.

That was the plan, JWST was supposed to cost 1B$, not 10B$. And then we were supposed to start building other telescope based on the lesson learned with that design such as: https://en.wikipedia.org/wiki/Large_Ultraviolet_Optical_Infr....

But it ended costing 10B$, not because that's what anyone wanted, but because that's what happens when you try to push the enveloppe. Just like the A380 program ended up costing 25B instead of 9 planed.

> Instead, one makes redundant systems. It is far, far cheaper, and yet more reliable than going for perfection

The JWST does not have 390 single point of failures like the media like to say, a lot of those are highly preferable but not make or break: If the mirror wings failed to deploy, JWST would still work at a lower res. If some of the sunshade layers didn't deploy correctly, it would still work. If the momentum flap didn't deploy, it would still work but require more fuel to keep orbit stable, lowering life expectancy of the missions, Latching mechanisms and release bolts where all designed with tolerance for some of them to fails etc.

There are was actually just a handful of true single point of failures with no redundancy.

> But I do know how airliners are designed and built

Yes I think by now we are all aware since you keep mentioning it in every single one of your comment. And I don't doubt that you know what you are talking about when discussing airliners, but it also seems to me that your experience is a hammer and now everything you see looks like a nail to you.

What I find irritating, is that the team that build the JWST is made of many, many highly intelligent individuals that thought about about how to best respond to the need of astronomy over 25 years, and you seem to think that they are complete idiots that didn't think about solutions and problem that you can think of in 5 minutes on hacker news. They have. A lot of those people come from the world of airplanes. One the biggest contractor for the JWST is Lockheed, which knows a thing or two about designing airplanes and asssembly line.

Hubble, was actually built like that, as it's actually a repurposed KH-11 reconnaissance satellite. Lockheed built 18 of those. Only one of them was ever ordered for astronomy.

So do not worry, JWST is built like it is, not because no one thought about your ideas before, but because they don't help solve what we actually care about.

Apparently NASA and the Soviet Union used to build duplicates:

https://flyingbarron.medium.com/the-james-webb-space-telesco...

so it's not such a ridiculous idea after all.

Intelligence has nothing to do with it. All you have to do is look at the space shuttle design. It was a seriously flawed concept. I did not understand how that concept could have been pushed forward. So I emailed Homer Hickam about it, wondering what I missed. He said I was right, and that he'd also thought the concept was completely wrong. Events later showed both of us were right in every aspect. (I had not expected a reply from him, but he was very nice to do so!)

The Fukushima reactor and the Deepwater Horizon drilling rig were also designed and built by experienced, intelligent people, but they both could have used experience from the airline people. Both had multiple single points of failure, which failed, and none of those points had to be there. I see this again in the auto industry, in particular Toyota's onboard computer.

The software industry is also full of the smartest people I know. Yet I've been able to bring in ideas from airliner design that are of significant benefit. For example, "defensive programming" comes from a talk I gave in the 1990s.

I recommend James Burke's "Connections" series. It is a history of technology, on the theme of how outsiders repeatedly spark advances and innovation by seeing things that the insiders don't see.

I'm an outsider as far as space probes go. I know little about the details. But that also means I am not immersed in the conventional wisdom that develops around the insiders of every profession, and sometimes and outsider can see things the insiders don't.

I don't claim I'm always right. But all I ask is to keep an open mind. Sometimes an outsider with experience in another industry can make a connection.

It seems that NASA and the Soviet Union used to build duplicates.

https://flyingbarron.medium.com/the-james-webb-space-telesco...

They technically did build duplicates of some (not exactly which missions, possibly all) rovers because of the communication delay i.e. you practice the dance moves on earth then send them to mars since you can't really do anything once it gets going.

How does this compare to the 'man on the moon' projects of China? It appears that from a purely scientific standpoint, this telescope will have a bigger impact than those of other space programs. Is my thinking on the right track here?

Also, is this complementary in function (and mission) to the Hubble? It appears to me that the spectrum is split up between Hubble and James Webb.

As an aside, it is interesting that the telescope is named in honor of a Lawyer turned administrator of NASA, James Webb (https://en.wikipedia.org/wiki/James_E._Webb). He must have been very capable indeed (or perhaps had the talent of attaching himself to very successful programs) because he was tapped by Kennedy to lead NASA at a time when the space race was at its peak. What's also weird is that James Webb worked as an administrator in all sorts of Government departments before being tapped to run NASA.

> How does this compare to the 'man on the moon' projects of China?

I don’t think space research has to be a zero sum game with one prescribed approach. The nature of research is that we need a multiple pronged approach into the unknown. If CNSA wants to pursue ‘Man on the Moon’ or JAXA wants to study asteroids, I see this as a win for humanity.

Programs like man on the moon make their contribution to mans knowledge through the engineering required to achieve the end, rather than in what they discover when they get there.

> Also, is this complementary in function (and mission) to the Hubble? It appears to me that the spectrum is split up between Hubble and James Webb.

Hubble's IR compliment was spitzer until it ran out of liquid helium. Webb is spitzer's replacement, with orders of magnitude more resolution.

Spitzer has qualified a lot of interesting mid IR targets to go look at in more detail.

In general non-vis space telescopes are more interesting than visible spectrum ones: Our vision only covers one octave so the odds that some random important physical process will best be observed in the visible spectrum isn't that great.

The visible spectrum is also the same spectrum that is well transmitted by the atmosphere so many vis observations can be conducted from earth with much larger and less costly instruments. Adaptive optics can mitigate atmospheric distortion at least somewhat, but there is no solution to non-transmission but space.

The atmospheric transmission has a two fold impact too: To study the atmosphere of extrasolar planets we need to study wavelengths that their atmospheres block. ... which, of course, are also wavelengths that our atmosphere blocks.

The picture is a visualisation, but does the telescope have a camera pointing at itself?

No. https://www.space.com/amp/james-webb-space-telescope-no-came...

Alas no its too dark on the cold side and far too bright on the hot side, no camera can work in these extremes. Everything we know is based on telemetry and they set up a 3D model based on the telemetry so that we could see the live state.

(This comment was posted in response to https://twitter.com/NASA/status/1479837936430596097, so that's the picture)

As others have noted, no.

Ground-based observations of the JWST are possible. They're rather more in the style of Seurat than Hirothropologie, and rather minimalist-pointilist at that.

https://www.space.com/james-webb-space-telescope-video-image...

Maybe we could use the Hubble space telescope to make a photo from the James Webb telescope ;-)

I wonder if there are some aliens looking at this, and wondering if another advanced civilization has put this together (just like we were wondering with ʻOumuamua). To me James Webb looks definitely like alien technology, if it manages to pass 50 deployment stages, depending on 178 deployment mechanisms... The team working on this did an incredible job! https://www.youtube.com/watch?v=uUAvXYW5bmI&t=195s

i'm sure they might when the light reaches them, given the context of planets in our neighborhood, probably in a few hundred/thousand years?

not if they know how to bend it ;-) I was told that even the speed of light is hackable!

For some light speed hacking porn I'd recommend reading Cixin Liu's In Remembrance of Earth trilogy. It has a few deus ex machina moments but overall it's just pure fun.

I understand that it will take months to perfect the primary mirror alignment and focus for good science data, but when can we expect the first image?

> Some high priority scientific observations (GTO & GO) with the JWST are likely to be carried out during the commissioning period, since it is clearly desirable to begin to take science data as early as is technically feasible.

> Early Release Observations (EROs) will be taken by JWST during both the commissioning and post-commissioning phases of operation. These observations will be chosen to have wide public appeal and are designed to demonstrate the capabilities of the JWST instruments. Publication or reporting in any form of results of these observations is embargoed until the EROs are released.

https://jwst-docs.stsci.edu/jwst-opportunities-and-policies/...

There is a chance for first images to be released before commissioning is complete, but no dates announced so far.

I've never been one for being hyped about telescopes, but I am particularly excited about the images that this one will come up with.

What kind of images can we expect? I understood it's an infrared telescope. Will we get visually ... interesting images? Or just data?

Public perception is always part of big budget projects like this. They are most likely releasing some outstanding "enhanced" visually interesting images

I'd like to see the scientific community get more throughput. While the launch of this telescope is great, it cost wayyy more than anyone expected and took far too long.

I hope all the applause doesn't drown out the criticism on the badly run operations and manufacturing capabilities at NASA that contributed to the delays.

Couldn't we make a photo of the deployed James Webb telescope from the Hubble space telescope?

Amazing design.

Was worried for a moment when they picked up heat issues during deployment but could resolve it a million miles away.

Well done to NASA/ESA/CSA/Northrop Grummam and all others who worked on it.

So now we just have to worry about the spacecraft ever losing attitude control, since exposing the telescope and its instruments to sunlight now will permanently damage them.

> Next up for Webb? Five months of alignment and calibration before we start getting images

I thought the L2 insertion burn was the next thing. Has that already happened?

From the Where_Is_Webb site, insertion doesn't happen for another 2 weeks. Like coasting up a hill half the time to L2 has elapsed but 75% of the way there (50% of the way in the first few days!).

The next thing looks like aligning the mirror segments. See the status bellow. I think there were already two relatively early correction burns.

https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html?un...

It has not happened yet. See: https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html

However, the alignment and calibration starts soon, before the l2 insertion burn. It will just continue for months afterwords, too.

Curious did they do a sample data with current temp? Since the deployment is complete. I know it will be not as good as at L2, but still.

They have to wait for the instruments to cool down some more first. Data is expected in 5-6 months.

I wonder when it can start observing.

It'll take a few weeks after L2 insertion to cool the components and another 5 months to calibrate the instruments.

I'm hoping that the 5 months of calibration time is one of those where the engineers were asked "how long", so they thought about it and then padded the shit out of it, then the PMs took that number and padded it yet again. After all that, it only takes a few weeks. It'll be the first milestone JWST would meet early, so not too likely. We've only waited decades, so a few more months isn't that bad. At least it is off the ground now!

Similar question was just asked during press conference and the answer was "telescope is cooling a bit faster than we simulated but it is not a significant difference, it might be ready one or two days ahead of current estimation".

Current timeline is for getting all 4 cameras to work, but I think only one needs cryogenic cooling, other 3 could work with just sunshield. In another answer one of the engineers said that first images will be released once telescope is fully operational (aka all 4 instruments cooled down).

Surely, it can take pics during this time with suboptimal cooling.

Probably hard to resist the temptation:)

There might be good engineering reasons to experiment early, like testing comms systems etc

It will surely take plenty of engineering and calibration photos during that time. I don't think they will be published instantly because telescope operators want to make a 'wow' effect with first photos from JWST.

Here is first technical image from Hubble, before its mirror's flaw was discovered: https://stsci-opo.org/STScI-01EVTBEME0059ASGX8X3DFWZMX.jpg

I can tell, you're an engineer. Of some variety.

I only play one on TV ;-)

Then again, it's not a unique situation for an engineer. It's the same for any situation for construction (and related jobs) estimates, auto-repair, etc. You always want to lean on over estimating time and finishing "early" vs the opposite.

https://jwst-docs.stsci.edu/jwst-opportunities-and-policies/...

There is a chance for first images to be released before commissioning is complete.

When is first-light scheduled for?

As all the unfolding SPOFs have finally been overcome, the title deserves an exclamation point.

How long before we can see images?

Awesome news. How much longer untill it gets to its destination and sends data and observations?

https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html?un...

Another while to go - 2 weeks left to its destination, but several months (~5?) of setup and calibration once it gets there.

I’m glad we got this good news. I would have been truly depressed if it had failed.

I can't help but be a little sad. JWST will be an incredible tool for scientific discovery, but its sensitivity range means it will never produce the kind of compelling imagery that Hubble did. Those pictures played a role in inspiring many of the people in the field today.

I would not be so sure about that. Many (most) astronomy photos are false color photos from quite different wavelength regions (often several different overlayed ones). So I do expect some fascinating images to come out of jwb as well.

Exactly this. Just google "infrared images of space", it's all false colors but still incredible pictures.

Fascinating, sure, but Hubble has almost six times the frequency range of Webb. In terms of magnification and dust penetration Webb is leagues ahead, but for a given magnification Hubble just sees a wider variety of stuff.

Can't wait for the first science results from JWST. Any predictions?

"We apologise for the inconvenience." written in the deep IR background.

Great news! I’m happy about this. Just curious - had this mission critically fail, how likely would we be to simply try again? Who needs to approve the cost for that? Would it be politically important to succeed currently?

I don’t think there was a way to fix it remotely. It would just do minor science missions with whichever instruments actually worked.

Sorry - by ‘try again’ I meant build a new one and launch it

Hopefully it inserts into L2 orbit successfully and starts doing science. If the results are interesting I can well see a future mission to try and refuel it to extend its life past its projected 10+ years.

https://www.cnn.com/2021/12/30/world/james-webb-space-telesc...

“It also used less propellant than planned due to the precision of the telescope's launch aboard the Ariane 5 rocket, so "the observatory should have enough propellant to allow support of science operations in orbit for significantly more than a 10-year science lifetime," according to NASA.”

Most excellent!

An incredible feat by all the engineers working on this!

Do we see anything up there yet?

A months long alignment period will follow, where the hexagonal segments are bent and turned by thousands of actuators until they are all focused to wavelength precision.

The first images will follow, but not before the dark side cools enough to not flood any interesting target into locally generated infrared.

Family guy has got to me, i keep thinking of James Woods high.

Amazing feat of engineering. NASA can be proud of achieving something that no other space agency could do. It took courage to keep shovelling money and effort into this project and some amazing science to get it deployed into space.

I agree with the sentiment, but I think some people might take issue with the suggestion that this was entirely NASA's achievement.

Who else was involved?

ESA and CSA to name a couple. Probably also lots of other uncredited, small cross-institutional interactions. Not to mention all the details of the launch. I was partly trying to speculate as to why the comment appeared to be getting down-voted. But I guess it's also my opinion that it's kinda weird to claim that no one else could have done it. Who else are we talking about other than earthbound humans?

https://en.wikipedia.org/wiki/James_Webb_Space_Telescope#Par...

NASA, ESA and CSA have collaborated on the telescope since 1996. [...] ESA is providing the NIRSpec instrument, the Optical Bench Assembly of the MIRI instrument, an Ariane 5 ECA launcher, and manpower to support operations. The CSA will provide the Fine Guidance Sensor and the Near-Infrared Imager Slitless Spectrograph plus manpower to support operations.

Several thousand scientists, engineers, and technicians spanning 15 countries have contributed to the build, test and integration of the JWST. A total of 258 companies, government agencies, and academic institutions are participating in the pre-launch project; 142 from the United States, 104 from 12 European countries, and 12 from Canada. Other countries as NASA partners, such as Australia, have or will be involved in post-launch operation.

ESA and CSA seem to be in every headline so I wanted to emphasize that only one org would've poured so much money into a project. NASA gets way too much flak and little credit these days.

I'm European btw.

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