JWST shade in the made

By Phil Plait | March 4, 2010 8:00 am

The James Webb Space Telescope is NASA’s successor to Hubble. Mind you, it’s not a replacement: JWST will see in the infrared, peering deeper into the Universe with its ginormous 6 meter unfoldable mirror than Hubble can.

But that infrared part is important. Objects that are warm give off IR light, and if you don’t cool your telescope, it’ll glow in the wavelengths you’re trying to see. It would be like having a flashlight shining down your ‘scope!

So JWST has to be cooled, and since it’ll be in a spot in space where the Sun shines 24/7 (the so-called L2 point, where the Sun’s and Earth’s gravity balances), it basically needs a sunshade. And also since the ‘scope is pretty big, the shade itself has to be sizable.

What engineers came up with is a multi-layered blanket of material that will sit "underneath" the telescope, blocking the sunlight and passively cooling the whole thing. The shade will be pretty big, about the size of a tennis court! To make sure it works, they created 1/3 scale model of the actual shade. This diminutive has been built, and is now undergoing tests at Goddard Space Flight Center.


[Click to deployenate]

Cool! Um. Literally.

You can also keep up with the construction of JWST using a webcam mounted in the clean room. I remember that room well; though I never got in I used to watch them work on Hubble cameras there.

Also, to give you an idea of just how big JWST will be… In 2007, I was at an astronomy meeting where a frakkin’ full-scale JWST model made an appearance. Here’s a video I made about it:

I did my best with this video considering the day before I was dying from a norovirus. Man, I love Seattle, but that was a rough week.

Anyway, JWST is still planning a 2014 launch. If you like Hubble images, JWST will blow you away. Just the galaxy shots it will produce will be spectacular beyond compare. And the deep field images will go much farther than Hubble can, if you can imagine that! JWST is a revolution in astronomy waiting to happen, every bit as much as Hubble was. Let’s hope these tests go well, and we can get that bird flying.


Comments (26)

  1. Charles Boyer

    Question is, will JWST replace or supplant the HST?

    Oh, and let’s hope they get this one right the first time, especially considering that no repair mission will be possible.

  2. John

    No UV, and few visible bands make Homer something-something.

  3. Paul

    If the mirror is /un/foldable, how do they fold it for transport? ūüėČ

  4. serenity

    “Question is, will JWST replace or supplant the HST?”
    Listen to the beginning of the video :)

  5. Childermass

    I thought the reason for putting it at L2 was so it would be because the Earth would eclipse the Sun? An Earth-Sun L2 point has the Earth between itself and the Sun. Or is it because L2 is unstable that the shadow can’t always be depended on? Or is the size of the umbra too small?

    /Formerly “a lurker”

  6. Steve Adams

    Here are some images I took of the JWST model back in 2005. It was part of an exhibit at the Rochester Museum & Science Center sponsored by ITT: http://www.csh.rit.edu/~steve/JWST/index.html

  7. TGAP Dad

    @5 Childermass: As I recall, L2 is at the point where the sun is only partly shaded (ubmral or penumbral shadow, I forget which). So from that point, there will be a ring of sun shining around the earth. Most of the sun’s energy will be blocked, but not all.

    Phil: Is the sunshade fixed to the “base” of the scope, limiting the scopes view in order to keep the shade blocking the light, or can the scope articulate the shade to allow it to point to more places?

  8. Matt T

    I don’t think there’s anything in that that *doesn’t* make me all nerdily hot’n’bothered. Unfolding mirror, Lagrange points, IR ‘scope. Huhhuhhuhhuhuhuhuhuh.

  9. Jon Niehof

    I saw the “artist’s rendition” animation of the JWST unfolding a few weeks ago; you can see it yourself at http://www.jwst.nasa.gov/videos_deploy.html
    My only thought was: “Galileo high gain antenna.” I’ll keep my fingers crossed for awhile…

  10. Charles Boyer

    @serenity – “Listen to the beginning of the video :)”

    I will, when I get home. Right now, it’s blocked by the corporate firewall.

    In other space news, the x-37 has been delivered to the Cape for launch later this year. Methinks Atlas V once again will prove her mettle and demonstrate she’s the REAL rocket for the future…because she’s the rocket of the RIGHT NOW.


  11. ITSO! No apostrophe in “with its ginormous…”

  12. Yojimbo

    Very cool! Oh – sorry!

    And sorry, too, for the virus, Phil. We’ try to get rid of them, but… it’s the moisture you know.

  13. Any idea if it will be visible from Earth? With a reflective shade that size, it should be, even if it is within the penumbral shadow.

    If so, it will be a constant reminder of the space program.

  14. John Paradox

    The photo kind of reminds me of the ship in Flight Of The Navigator. Maybe it’s the silver shininess ….


  15. DennyMo

    A couple years ago I found a website for a guy who said he was a “Professional Origamist”. I looked at the paper cranes, frogs, and flying stars scattered about my desk, and wondered “How the heck does someone make a *career* out of this?!?” Turns out one of his big projects is helping NASA figure out how to fold/unfold stuff (like the JWST sunshade) for deployment in space. Wow, what a gig, just proves you never know where a hobby can lead you!

  16. jcm

    I read something similar in Sky & Telescope.

  17. From Wikipedia, for those who haven’t yet…:

    …It is, however, slightly beyond the reach of Earth’s umbra, so solar radiation is not completely blocked. The Wilkinson Microwave Anisotropy Probe, Herschel Space Observatory and Planck space observatory are already in orbit around the Sun‚ÄďEarth L2. The Gaia probe and James Webb Space Telescope will be placed at the Sun‚ÄďEarth L2.

  18. Bruce the Canuck

    What ever happened to the idea of an independent starshade spacecraft to enable the JWST to act as a planet-finder? It was discussed at Astro2010, but I can’t find much mention afterwards. Did it gain any support?

  19. “So JWST has to be cooled, and since it‚Äôll be in a spot in space where the Sun shines 24/7 (the so-called L2 point, where the Sun‚Äôs and Earth‚Äôs gravity balances)”

    Is this a typo? The L2 is ~1.5 million km OUTSIDE the Earth’s orbit. This puts it on a place where the sun shines 0/7, i.e. never.

    The reason it needs a screen is due to the sunlight refracted in the Earth’s atmosphere and also the blackbody radiation of the Earth itself.

  20. Lifesigns (#19): That’s not correct. I left off details, but JWST will be in what’s called a halo orbit around the L2 point, so it will actually only rarely be in the Earth’s shadow. It would be a bit inconvenient for it to be in the Earth’s shadow when its power is generated by solar panels!

  21. Hi Phil. Thank you, that was a detail I had missed. I stand corrected. It is no small feat they’re pulling off then if the mirror is to reach 40 K while the spacecraft is exposed to direct sunlight.

    And I sincerely hope they do, the JWST is one of the top most promising missions in the few coming years. If only now the space agencies could join forces and build a large interferometry telescope like HST or Darwin.

  22. Jim A.

    I have a stupid question: What prevents black body radiation from the first layer of the shade simply heating up the second layer, and it the third layer etc.? If the answer is re-radiation in other directions, wouldn’t putting the layers further apart be more efficient? Smarter people than me have been working on this for years, so i’m obviously missing something. I just can’t figure out what it is.

  23. Messier Tidy Upper

    Nothing can replace the Hubble Space Telescope. :-(

    Follow on from & do some amazing different stuff sure but not “replace” – not to me.

    Heck, it isn’t even a visible light scope. I look forward to having the JWST flying and all but it won’t be the same.

    I hope they keep the HST going – for as long as is remotely possible.

  24. Just call me Jim

    What is it about Seattle and norovirus? My son and family lived in Seattle for five years, and three, count it, three times I and my wife had the devastation of norovirus in about ten visits.

    Makes me want to go total homeopathic just as a personal test. Damn, norovirus is the absolute worst vomiting disease on the planet.

    If Gawd could have done it, norovirus is the perfect punishment for every transgression. It must be worse than stoning, evisceration, and conflagration. Boils and blood come nowhere close to the pain and suffering of norovirus.

  25. dcsohl

    How do they manage the L2 point? I see there are already three observatories in “halo orbits”, with two more planned, and almost certainly more after that. I’m presuming there’s some sort of management to ensure these craft don’t collide, but how does that work? And how big are these “halo orbits”?

  26. Thanks for the great article!

    The 1/3 scale sunshield is actually being tested at the Nexolve Facility in Huntsville, Ala.

    Our Goddard cleanroom currently has the flight ISIM (the structure that will hold all the instruments) and test versions of two of our instruments, the NirSpec and MIRI.

    Someone else already pointed out our deployment video, but we have some pics of what it will look like in the rocket too:


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