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Comment by lainga | Hacker News Reader

I can't find an answer to this anywhere: is there a backup JWST (or parts thereof) if this one fails to launch?

To me, this is a major dysfunction of the NASA model.

Why wasn't 5 Hubble telescopes launched? The marginal cost for the other 4 must have been vastly smaller than the first. Observation time on the original Hubble is still, after 30+ years a scarce resource. With 5 of them, we could have gotten vastly more science done at smaller cost.

I don't have a fully fleshed out theory for why, but part of it is that NASA as a government organization is ultimately a political endeavour, and it will have to optimize for what makes politicians look good in the press, rather than what gives the most science bang per buck.

Even in high school robotics we built a main chassis and a 1:1 spare for testing and hot swapping parts.

There was. Sort of.

https://en.wikipedia.org/wiki/KH-11_KENNEN

In particular some of the manufacturing tooling for the mirrors were shared, leading to the HST mirror being downsized to 2.4 meters.

Its surprising how many people don't know this all these years later. Hubble is repurposed spy satellite. The main cost of the vehicle isn't in the spacecraft itself though its the optics which are different from those used on KH-11. What is good for looking at Russian military bases doesn't directly translate to looking at galaxies.

In fact, the NRO donated two Hubble-like KH-11s in 2012, on the condition that they not be used to observe Earth.

https://en.wikipedia.org/wiki/2012_National_Reconnaissance_O...

One of them forms the base of https://en.wikipedia.org/wiki/Nancy_Grace_Roman_Space_Telesc....

The person or persons, at the NRO or whatever other clandestine agency, who championed this donation, over what must have been very considerable hand-wringing about the consequences of giving this technology to civilians, are very fine people.

The story from the astronomy side was that the 2.4 meter mirror was mysteriously inexpensive compared to anything else in the R^2 mirror cost curve.

It's a little odd how people re-tell that story, but ok.

The techniques and tooling can be fit for both purposes but the telescope you build to look at something 250km away at high resolution and illuminated by the sun and the one you build to look at galaxies thousands of light years away that are fainter than can be seen with the naked eye are very very different.

Hubble's optics also weren't easy to produce and notoriously were faulty which had to be later corrected in orbit with a Shuttle mission. The bid being lower than expected could just as easily be explained by the contractor massively under bidding to win the contract. I've never heard anyone claim the Perkin-Elmer also made the optics for the KH series before now. Its not outside the realm of possibility but unless you have some compelling proof then I have no reason to believe that. I think the fact they screwed up indicates they probably weren't because if they had done the optics for the KH-11 series then they would have been well practiced at making mirrors that size by the time Hubble was built.

I'd expect the largest part of why is that the marginal costs of launches to space unfortunately don't go down. Each launch is nearly as expensive as the first. The marginal cost on the ground is one thing, and it sounds like Nasa often builds things in triplicate or more on the ground, but then uses the parts in training exercises or for debugging purposes. Nasa probably made three or four equivalents to Hubble. Probably plenty more than that to do all the underwater training on the incredible repair missions for Hubble that extended its lifetime from a projected 5, then a sad "failed mission", then finally the 30+ years we should be grateful to have gotten at all.

They just have never had the budget in launch costs to ever launch more than one.

> the marginal costs of launches to space unfortunately don't go down

Until recently, neither launch nor satellites had economies of scale. With reusability, launch does. And with common platforms and constellations, satellites are beginning to.

>marginal costs of launches to space unfortunately don't go down.

Some aspects certainly do, like ground-support-equipment and basic launch infrastructure.

Even in the Hubble days, launch costs were a relatively small piece of the pie compared to the costs of actually building the thing. I think for Hubble it was less than 10% (depending on how you count the servicing missions). For Webb it's significantly lower.

> Why wasn't 5 Hubble telescopes launched? The marginal cost for the other 4 must have been vastly smaller than the first.

Economies of scale only apply at, well, scale. Five Hubbles would cost 5x one Hubble to construct. There's very little in the way of savings because most parts are custom fabricated. The parts need to be tested, integrated, then tested after integration. The testing and verification of each subsystem takes the same number of person-hours. So testing 5x the systems requires 5x the time.

You can't just accept a high failure rate of something the size of Hubble just because you've built five of them. If you launched a Hubble and it failed in some Loss of Vehicle fashion after inserted into orbit you've got a big uncontrollable mass of telescope flying around the Earth.

Even if we still had the Space Shuttle (or a fantasy version of the SpaceX Starship) flying an uncontrollable Hubble couldn't necessarily be retrieved. If it wasn't accepting commands and was spinning on some axis it would be too dangerous to approach with another vehicle. Even an unmanned vehicle couldn't necessarily approach it without a collision that causes even more problems. See the recent idiotic Russian ASAT test for an object lesson in what could happen.

This is all to say you don't want some large satellite in a long lived orbit to fail. So there's no savings on testing and verification. Even though at launch Hubble's mirror had problems the satellite itself was fully under control and operable.

Something like Starlink is very different. All the satellites in a given block are functionally identical and fungible. If one fails it's easily replaced by another. They also deploy to a low unstable orbit. If a Starlink satellite fails and is uncontrollable it will de orbit by itself quickly. They must be functional to enable the onboard engines that get them to a stable intended orbit. A Starlink satellite then needs far less testing and verification than a Hubble or JWST, not that they can be poor quality but they don't need to function Or Else Bad Things.

Is that really true? I'm guessing a big part of the cost is figuring out how to actually invent stuff needed for the project. That knowledge is now known. That cost is now 0.

>There's very little in the way of savings because most parts are custom fabricated. The parts need to be tested, integrated, then tested after integration.

To piggy back on the the GP's point, the fabrication research is only one small cost center. Quality control costs much more in aerospace than many people realize. The reason why a bolt may cost $150 is because it has to be tracked, material coupons kept/tracked/tested, held in bonded storage etc. and not because we had to figure out how to make a bolt. Those costs don't come down as much with scale as, say, raw material.

If it were all about knowledge costs, many designs today would be dramatically cheaper because many use technology (and even refurbished rockets) from 50 years ago.

Just because the knowledge exists in the world doesn’t mean that you know it. Consolidating knowledge is a non-trivial exercise.

> I'm guessing a big part of the cost is figuring out how to actually invent stuff needed for the project.

We're talking about marginal costs, not development costs. So the cost to invent a component is already out of the equation. The high production cost of something like Hubble comes from testing and validation more than materials or fabrication.

The failure modes for something big in space can be extremely dangerous. Even a tiny "cheap" cubesat requires a lot of relatively expensive testing so there's a reasonable assurance it won't fail in some catastrophic fashion and destroy the entire rocket.

Testing space hardware is additionally difficult because you can only just approximate the hardware's operating environment on the ground. Space hardware also can't be easily repaired or repaired at all once launched. So you've got to test actual flight hardware and if it fails possibly rebuild it from scratch testing and validating the entire way.

Developing space hardware and high precision science instruments is expensive and difficult. But it's just a small portion of the overall mission cost for something like Hubble or JWST.

I defer to your knowledge, i'm not trying to be a jerk. But Hubble took like 30 years? or so to develop and build? How long would a second Hubble take? I'd have to imagine it's less than 5 years, no? That has to be a huge cost savings. The testing process would have to be more streamlined or efficient, i would think. You have a much better understanding of failure modes.

The Hubble took a little over ten years to build and develop. It's launch was postponed to 1990 because of the Challenger disaster.

> The testing process would have to be more streamlined or efficient, i would think.

Why do you automatically assume testing for a complicated and delicate machine is inefficient or not streamlined? That's a pretty bold assumption with zero evidence.

Understanding failure modes doesn't help test and validate something any faster. There's a finite number of hours in a day and components need some proscribed amount of testing.

Hubble took ~12 years from initial funding to launch with the challenger disaster postponing it 4 years out of that. Additionally if the decision was made to use traditional mirror techniques the Hubble was predicted to launch in 5 years already, instead of the difficulty they found with the alternative method but they didn't know that at the outset.

You will encounter different bias the second time around. Although maybe this kind of stuff is less common in space industry. People could want to correct the mistakes of the first time. Spend time optimising things and taking more time. And people could take learned knowledge for granted and assume success was based on that.

If they had built five Hubbles that each had defective mirrors and all of them needed a shuttle visit to correct the issues and make them usable...

The US absolutely could've built 5 Hubbles - because it did, they just don't look at Space - they look at Earth. The Hubble is basically a KH-11 spy sat chassis. NASA was given a gentle suggestion that if the optics package was a particular size, there was definitely a company in the US which could polish lens and mirror packages of exactly that size.

[1] https://en.wikipedia.org/wiki/KH-11_KENNEN

That would require staffing up for the production run and then firing them when the contract was finished. There is a limited volume of sporadic work available for contractors to bid on. Increasing production capacity doesn't increase demand. At the end of the day public investment into science is always a jobs program first.

NASA was trying to get some form of series production for base system bus for long distance probes in late 1980s.

What happened was that pretty soon the budget got slashed, and the out of the prototype two units they barely scrambled to have one of them flown, with very complex process to balance the budget in face of constant attempts to cut it by Congress.

Maybe if NASA's budget was allocated in different process, things would be different. As it is now, the people controlling the purse strings care about their reelection so they will at best jerk projects around to send money to their states, or to place their own spin on things, etc.

Relatedly, I'd be curious to know what the split has been of the $10B "program cost" in terms of development vs manufacturing.

I assume that like with most things, the vast majority of the cost has been in the design and documentation over its 30 years of development. At the same time, there's obviously a ton of extremely high precision bespoke components in there, so "building another one" would definitely not be trivial.

If it's anything like the hardware engineering programs I've been involved in, at qty=1 the cost is almost all R&D. That includes development of processes to build something like 1.3m wide ultraprecise beryllium mirror segments...

Oh absolutely, but I still wouldn’t be surprised if the cost for unit 2 was still another half a billion dollars. It would be fascinating to know.

Aerospace isn't necessarily like that for a number of reasons. A large driver of cost is quality control. For example, when a custom part is manufactured it needs to go through a number of tests, some of the raw material needs to be kept and tracked for future testing, etc. When they get shipped they have to be be tracked and handled differently, sometimes accelerometers are placed on the cargo to measure any shocks, etc. They need to be stored in a bonded warehouse, often climate controlled throughout its life. All of that control, testing and documentation adds to the cost even after R&D is a sunk cost.

The answer is no for mainly two reasons:

1. Prohibitive costs. Its extremely expensive (both in money and time) to manufacture many of the parts of the telescopes, such as the reflector dishes. Its even more expensive to do all the testing & certification of the manufactured parts.

2. Its all outdated anyways. The JWST project has been ongoing for literally decades (starting in '96 if I remember). If we were to start from scratch today we would make a lot of different design choices based on more recent technological developments

I would love to see a video where one of the engineers on the project talked about what would be different if Webb was started today. Materials, software, processes, everything!

A huge design issue that might - or might not - be pushed would be the power system.

Solar panels require that JWST stays in the sun while conducting observations, while at the same time being critically dependant on the observing equipment to be cool - and being unable to just keep it inside bigger structure like with Hubble.

This means that there's a huge problematic sun shade structure which is considerable part of the SPOFs still endangering JWST even if it is inserted into orbit correctly.

It's worth considering that nowadays we don't really do backup copies of satellites/probes because launch is pretty reliable by now, especially on rockets that have been flying for a while (which is pretty much a requirement to be chosen to launch a flagship project like JWST).

Ariane 5 has a long flight record with very few failures and the design has been further carefully reviewed specifically for JWST, with the previous two launches having served as verification for any fixes that needed to be made prior to flying this mission.

Basically, the chance of JWST being lost due to a rocket issue is much lower compared to the chance of it being lost due to design issues with the telescope itself.

This is our only shot. They didn't replicate the build.

https://www.quora.com/What-would-happen-if-the-James-Webb-Sp...

Imagine having the replacement gold reflector dish in storage somewhere.

Nope. Wouldn't be a good use of money anyways. If it fails, it might be because of a design or manufacturing flaw. Better to make the new one after we have some idea what went wrong.

I'm wondering why is that, which part of the effort was dedicated to research and how much time and money would it cost to build a new JWST?

The reasoning that I heard (and I hope I'm relaying this right) was that if it doesn't work then it will most likely be because of something that needs to be redesigned, so there's no point in producing an exact replica.

I think this assumes a successful launch and some kind of issue with the deployment.

The other concern is, of course, what happens if it blows up on the launchpad.

Presumably they've actually quantified these probabilities and think that the chance of that is relatively very low compared to the chance of something going wrong in the design. These things are not cheap, so it makes sense not to have to make three if the launch succeeds and design fails.

Oh yes, I totally agree— this is a very proven rocket, and the deployment sequence is very, very much not proven. So it absolutely makes sense to have gone this way.

That's assuming that anything that goes wrong in the deployment sequence necessitates a clean-sheet redesign of the whole thing. No reason to think that.

But with so many things that could go wrong in such a tightly integrated system, it's impossible to predict which components or assemblies may be affected by a partial redesign.

If you say so.

Ariane 5 appears to have 96% mean reliability. Source: 2021 Space Launch Report – Launch Vehicle by Success Rate (spacelaunchreport.com) - https://www.spacelaunchreport.com/log2021.html#rate

https://news.ycombinator.com/item?id=29554274

The footnote about Lewis Point Estimates is super interesting.

"Lewis Point Estimate Determined as Follows.

  Maximum Liklihood Estimate (MLE)= x/n 
      where x=success, n=tries
  For MLE<=0.5, use Wilson Method = (x+2)/(n+4)
  For MLE Between 0.5 and 0.9, use MLE = x/n
  For MLE>=0.9, use Laplace Method = (x+1)/(n+2)
 
  Lewis, J. & Lauro, J., "Improving the Accuracy of Small-Sample 
   Estimates of Completion Rates", Journal of Usability Studies, 
   Issue 3, Vol. 1, May 2006, pp. 136-150."

Concur. You have to see this thread on it in the NASA Spaceflight forum - https://forum.nasaspaceflight.com/index.php?topic=39928.0

I think OP means "what if the rocket fails".

The answer is that building another telescope specimen would be quite expensive, even without any changes to the design. The supply chains aren't set up for volume and integration and testing is very involved. I can't put a number on "the second telescope would be x% cheaper", but it would be very disappointing.

Also Ariane 5 is one of the most reliable rocket capable of launching JWST on the correct orbit.

It's also going out pretty far (the L2 Lagrange point on the other side of the moon), so they also won't be able to perform any manned post-launch repair missions like they did with Hubble.

Actually I have a question about this. What happens if it fails at L2? Is that position like occupied or more difficult to deal with from then on?

The L2 point is unstable do energy needs to be expended to maintain position there.

Solar wind will push it out of L2 and into an orbit around the sun. This is already going to happen once JWT runs out of fuel to maintain its position.

> so they also won't be able to perform any manned post-launch repair missions like they did with Hubble.

In terms of hardware that's readily or soon to be available, it is technically possible. Starship, if it gets off the ground, is the obvious choice. Orion could do it, but it would mean dumping another two billion into JWST.

If it really came down to it, Falcon Heavy launched with a Crew Dragon sitting on top of it could probably reach it, although it might need an additional kick stage (I haven't done the maths), and it would need to be crew rated first (and SpaceX don't currently have an interest in doing that).

If you consider the human to be part of that hardware, it's over 4x the distance that a human has ever travelled. There would still be a lot of technical problems to be figured out.

Having a ship and a launcher capable of reaching the telescope is a bit different of being able to service it. I understand that just planning and preparing a mission on this scale, with current technology and processes, would take more time than the service life of the telescope itself.

Also, AFAIK, Crew Dragon does not have airlocks or other resources for EVAs. Not sure it the capsule can be evacuated for that too. But I would like more information in this issue ... could not find too much from reliable sources for now.

> Having a ship and a launcher capable of reaching the telescope is a bit different of being able to service it.

True. But generally when people bring up the statement that we can't service it, they usually back that up by citing the distance. There would still be a lot of hurdles to overcome, but none are insurmountable with relatively small investment.

All of that said, if Starship works, then the economics change drastically anyway. You could probably launch an entire fleet of less reliable, but much cheaper telescopes, for less than the cost of servicing.

Webb is going to the Sun-Earth L2 (about 1.5 million km from Earth), not the Earth-Moon L2 (which is about 61,000 km from the Moon and 445,000 km from the Earth.

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

I'd imagine they just cannot fabricate the mirrors as many as they want. The mirrors, arguably the most important parts of any telescope or optical instrument, need delicate manufacture due to the required precision. At the end of the day, this is not automobile industry.

Makes me wonder if it would have been smarter to build it in a modular way with different pieces being sent up one at a time, assembled on the ISS, then launched in the direction it needed to go.

Then you have multiplied your launch risk by the number of launches it would take to get it up there, plus there is the difficulty of assembling it in orbit. The only other project built like that was the ISS, and it took decades and a launch vehicle that no longer flies.

The biggest problem would be that it would be in the ISS orbit, which would require a lot of delta-V to get it to its final orbit.

An advantage of assembling it in ISS orbit is that you have DEXTRE and a team of spacewalking astronauts available to do the unpacking and assembly!

Or an altogether different design: thousands of cheap, totally fungible sensors in an array at the L2 point.

Not only would they be replaceable, but we could increase capacity in the future.

Except that interferometry at IR is still extremely hard.

humanity has a lot of experience building reliable one-offs, actually a lot more experience and a lot better experience than with modularity and bits and pieces. I'm a software engineer by trade but every time I look into industry (ship building, skyscrapers, etc) you realize: that aphorism about software engineers, woodpeckers and civilization was absolutely right.

"If builders built buildings the way programmers wrote programs, then the first woodpecker that came along would destroy civilization." ~ Gerald Weinberg.

For those who don't know what the quote is. I found it here[1].

[1]: http://www.ganssle.com/articles/programmingquotations.htm

Can you explain the colloquialism a bit? Is it a knock on modular design?

Having worked both in construction and software, modular design seems fairly common in both.

No, and I think they should have made two of them.

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