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James Webb Space Telescope

jwst.nasa.gov

64 pointsantr37 comments

Hey, my job's on HN! I work on JWST (simulation software, among other stuff) and I think it's pretty cool too :)

As an astronomer who works on infrared data every day, I am really grateful for everything you guys are doing. What kind of simulation software are you developing?

I'm working on WebbPSF, a tool to simulate PSFs for the Webb instruments. I'm also adapting it for WFIRST, a future mission. It's going to be kind of like TinyTim is for Hubble when it's done.

Very cool. How much data is going to be arriving from JWST daily? Is it going to be readily open to the public?

> Is it going to be readily open to the public?

The scientific data will be available to the public, sometimes after a "proprietary" period (typically in the range 6–18 months) where the data is only accessible to the team who successfully proposed to obtain that data.

Not really my department! I do work at STScI, which operates the MAST archive that will eventually hold all this data, so I'm sure someone in my building knows.

My group at Goddard has done work on the JWST detectors. JWST is a big deal here. It also scares the crap out of me, due to the gymnastics that are needed to get it unfolded properly, in a location where repair is impossible. A lot of people will be very, very happy when this thing is in orbit and working.

What kind of detectors are you working with? Are they of a different kind or just more powerful than what's already up there?

Sorry, I'm just the sysadmin here. A lot of the JWST work was done before I got here, but we still help support them. I'm sure there is detailed information on the web about the detectors in use on JWST.

As excellent has Hubble has been, the JWST is going to put it to shame. The potential risk, however is that it won't be serviceable, as Hubble famously needed to be very early in its life. If all goes as planned, we're all going to have some really nice new desktop wallpapers in a few years. And, I suppose, a better understanding of the universe will be a nice side benefit.

Until this post I didn't realize it wasn't going to orbit Earth in roughly the same spot as Hubble -- it's going to be roughly 4 times further away from Earth than the Moon is, orbiting L2!

http://jwst.nasa.gov/orbit.html

I never understood how we can launch something into an L2 orbit. Does the rocket just fly out there and stop? Just it get caught at that location?

Here's the main reasoning for placing it at L2: http://jwst.nasa.gov/orbit.html

Right I understand the reason. But as my question says, I don't understand how a rocket inserts it into that orbit.

This video shows the steps that take it from a folded-up thing stuffed into a rocket to a deployed telescope at L2: https://www.youtube.com/watch?v=bTxLAGchWnA The rocket is out of the picture fairly early on in the timeline.

Whoa. A deployment sequence to put Curiosity's one to shame. Too many moving parts, over the course of a month. I hope all goes well.

It's easier to think of it not as "stopped", but in an orbit around the earth that takes exactly 1 year to complete. So it does have some tangential velocity.

If you're curious about orbital space mechanics, try Kerbal Space Program. You'll get a much better idea how NASA puts things into orbit after you've done it a few times yourself.

Basically, the rocket doesn't just fire in a straight line away from the Earth all the way into orbit. It starts arcing very soon into the ascent, and the thrust is nearly parallel to the Earth's surface for much of the journey.

That’s all well and good for most of the stuff humans do in space (and it really, really helps to get a sort of general, very basic and intuitive understanding of orbital mechanics), but KSP does not do Lagrange points at all. You cannot use it to get a basic understanding of how those work with KSP.

That's why our correspondent needs to install the Principia mod!

http://forum.kerbalspaceprogram.com/threads/68502-WIP-Princi...

The same way that you can push a ball just to the top of a hill. Very carefully, because if you push it too hard it will roll down the other side.

Check out https://en.wikipedia.org/wiki/Newton%27s_cannonball and http://www.scilogs.eu/en/blog/go-for-launch/2009-05-28/how-t.... To fly to the L2 point, you have to get your rocket into (an elliptical) orbit around the Sun that intersects with the L2 point. Once you get to L2, you have to match its velocity, which you do by firing your engines to speed up (or slow down) such that your rocket and the L2 point have zero velocity relative to one another.

While Kerbal Space Program's physics simulation doesn't have Lagrange points, you can get a pretty good feel for how they work by performing any kind of in-orbit rendezvous.

Interesting tidbit: JWST can't see blue. While Hubble could see entire visible light spectrum, astronomically infrared is more interesting. So JWST can see infrared, but not blue.

Astronomical images always have been heavily edited and it never was "what you may see", but it is more so for JWST.

It's not just that IR is "more interesting" (maybe it is), but it's much more difficult to see through the atmosphere. It's obviously cheaper and easier to build huge optical telescopes on the ground, but to see into the infrared, you need to get above the atmosphere.

Edit: source http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ir_tutor...

IR is profoundly more interesting, precisely because it is able to penetrate all sorts of media, most especially interstellar dust and gasses, allowing JWST (and others) to see stars that can't be seen by their visible light.

Regarding our atmosphere filtering IR: do you feel the heat of the sun when it shines on you? That's light. Infrared.

Edit: Additional point of fact: our atmosphere interferes with light by scattering it away from its angle of incidence. Light with a longer wavelength is able to get through without scattering (IR, red, orange, yellow, etc) light with a shorter wavelength (blue) is more likely to collide with a molecule of something on the way in, and it gets bounced around so frantically that all those blue light waves seem to kind of pile up and come from everywhere. No, our atmosphere's light transmission woes are much more deleterious to the smaller wavelengths of light than to IR.

True enough to the "notch filter" and the fact that the matter in the air emits IR radiation as well. IR still penetrates, visible light is scattered.

Aren't the mirrors coated with gold? If so, then they do reflect some blue, just not as much as the lower frequencies.

Perhaps the sensors are discarding that frequency.

This fella is down at Northrop in Smell Segundo! My Dad always shoots me a text whenever he's had a chance to look at it. He told me a neat story once about the mirrors inside it... that when he stood in front of it, he felt really strange. It's because the mirrors we are all accustomed to have so many imperfections compared to the types used in this device. He wasn't used to seeing such a perfect mirror image.

Ever tried cracking open a hard disk drive? Same thing. The reflection clarity is pretty shocking.

I wonder if there's a market for "premium mirrors" ...

Not to diminish the achievements of the opticians working on the JWST, but you can obtain the same level of perfection at home, using everyday tools. However, you'll be working on a much smaller surface.

Make your own telescope mirror. To pass the tests, it must follow the ideal surface with an error less than lambda/4, where lambda is the wavelength of visible light. In practice, that's 0.1 microns or less. Also, the density of scratches and pits must be very low (not detectable by usual means).

It's totally doable by hand, working in your garage, on a piece of glass the size of a dinner plate. It just takes a very, very long time, at least on first attempt. My first telescope took over a year (admittedly, I took too many breaks, and then I did a lot of experiments with the techniques).

http://florin.myip.org/blog/150-mm-f8-mirror-25-mm-pyrex-pol...

Telescope mirrors:

https://www.flickr.com/photos/nasawebbtelescope/page9/

https://www.flickr.com/photos/nasawebbtelescope/page11/

JWST vs Hubble: https://farm5.staticflickr.com/4076/4813007838_13c736d9ca_z....

Mirror curvature( large jpg ): https://farm5.staticflickr.com/4114/4813106662_0d3eeddc27_o....

Remember who runs congress now, prepare for it be canceled (again).

I saw this in Wikipedia:

"The JWST has a history of major cost overruns. In 2011, the United States House of Representatives voted to terminate funding, after about $3 billion had been spent and 75 percent of its hardware was in production. Funding was restored in compromise legislation with the US Senate, and spending on the program was capped at $8 billion. As of December 2014, the telescope remained on schedule and within budget, but at risk of delays."

Source: https://en.wikipedia.org/wiki/James_Webb_Space_Telescope

Some things ARE expensive because they are difficult, require quality components or processing. I would rather spend on difficult science than on dumb bombs...

I'm glad to see some folks on here involved with the JWST, thanks for all your efforts!

I have a question: is the big cost primarily due to the one-off nature of the components, figuring things out for the first time etc? I ask because there's some proposals (ExoEarth Mapper) for constructing a giant array of 20+ of JWST-like telescopes in order to get pictures of earth-like planets.

So if one JWST costs $8Billion, how much would 25 cost?

Also check out: http://jwstsite.stsci.edu/webb_telescope/

STScI will be the Science and Operation Center for JWST.

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