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Webb: Sun shield deployment completed

Engineers today successfully completed the full deployment of the sun shield of the James Webb Space Telescope.

The unfolding and tensioning of the sunshield involved 139 of Webb’s 178 release mechanisms, 70 hinge assemblies, eight deployment motors, roughly 400 pulleys, and 90 individual cables totaling roughly one quarter of a mile in length. The team also paused deployment operations for a day to work on optimizing Webb’s power systems and tensioning motors, to ensure Webb was in prime condition before beginning the major work of sunshield tensioning.

The process took eight days, and was by far the most complex such remote deployment ever attempted by an unmanned spacecraft. The shield is now in place to shade Webb from sunlight and heat and thus allow it to observe very faint infrared objects billions of light years away.

Next comes the deployment of Webb’s secondary mirror, followed by the unfolding of its main mirror.

Genesis cover

On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.


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  • Robert Pratt

    Go Webb, Go! For what it cost it darn sure better work.

  • David Eastman

    Great news that everything seems to be working. But it really chaps me when NASA press comes out on something like this or SLS and starts proudly listing the massive number of parts, and the enormous length of capable, and I’m sitting here thinking “and how many of your engineers are staring at those numbers and hanging their heads in shame that they couldn’t design something simpler to do the job?” KISS and “the best part is no part” are quoted often for good reason.

  • John

    Yeah it better work, or they should dock the paychecks of the managers until it’s paid for!

    I was surprised to read that it only has fuel for something like 5 years, but they can extend that due to the efficient trajectory so far.

  • David Eastman

    Usually when we refer to fuel and lifespan on a satellite, we’re referring to actual propellant for manuevering, and so a good launch and efficient trajectory management can extend time on station. In the case of Webb, the limiter isn’t likely to be maneuvering fuel, but coolant for the sensors. It has enough coolant for the planned five year mission with some unspecified margin, presumably at least to seven years, but once the coolant is gone, it’s mission over. I haven’t seen a technical discussion of what kind of coolant is used and how it’s consumed, I don’t know if its just a set amount of temperature that can be cooled, or if they expect chemical decay, or just minimal leakage that will eventually exhaust the supply.

  • wayne

    Great questions. Just did a quick search. The JWST / NASA website has a lot of info.
    (I have not been following this closely, it feels like this has dragged on for decades…)

    For the (mid-infrared) MIRI instrument, they initially designed a system that consumed coolant, but then switched to a closed-loop “refrigerator” type system, which is only limited by mechanical wear-n-tear on the parts.
    –direct hot-link to a PDF
    “This paper will discuss how a significant change to the MIRI Cooling System from a solid hydrogen Dewar to a Cooler was achieved after the instrument Preliminary Design Review (PDR), and it will examine any system compromises or impacts that resulted from this change so late in the instrument design. A general overview of the Dewar and the Cooler systems management, the roles of the systems teams in the different organizations, how the requirements are managed in such an elaborate environment, and the distinct design and Integration and Test (I&T) challenges will also be provided.”

  • wayne

    here we go:

    “MIRI Cryocooler”

    in brief, in part–
    “Three of Webb’s four scientific instruments “see” light with wavelengths from 0.6 microns to 5 microns. These instruments have detectors formulated with Mercury-Cadium-Telluride (HgCdTe), which work ideally for Webb at 37 kelvin. We can get them this cold in space “passively,” simply by virtue of Webb’s design.”
    “Webb’s fourth scientific instrument, the Mid-infrared Instrument, or MIRI, “sees” mid-infrared (MIR) light at wavelengths from 5 to 28 microns. By necessity MIRI’s detectors are a different formulation (Arsenic-doped Silicon (Si:As)), which need to be at a temperature of less than 7 kelvin to operate properly. This temperature is not possible on Webb by passive means alone, so Webb carries a “cryocooler” that is dedicated to cooling MIRI’s detectors.”
    “The primary piece is the Cryocooler Compressor Assembly (CCA). It is a heat pump consisting of a precooler that generates about 1/4 Watt of cooling power at about 14 kelvin (using helium gas as a working fluid), and a high-efficiency pump that circulates refrigerant (also helium gas) cooled by conduction with the precooler, to MIRI.”

  • pzatchok

    I am very happy about this launch and deployment.

    For all my carping about the price I am just happy its working 100% so far.

  • Jeff Wright

    It has fuel for ten years due precision of Ariane 5. Old Space’s finest moment since Apollo and the Voyagers.

  • LocalFulff

    JWST is the Apollo project for space telescopes. They went into it way over their heads. But they pulled it off! Like the LIGO gravitational wave detector. Sounds hopelessly impossible, but they did it. To further research it is not to make copies of existing telescopes that would see more of the same. One has to create observatories that see what ahas never been seen before.

    The scandal, I think, is that the big problems (in recent years anyway) have been about the spacebus, things that thousands of satellites have, and the sunshield. Those are not the most advanced things on JWST, they should’ve worked during their final tests on the ground, but they failed. Thus at least the last few years of delays and budget overruns. I dodn’t really follow the first decade or so of JWST development, so I don’t know what went wrong before that. Anyway, the spacebus and sunshield failed on the ground, so it was fixed and now it works.

    If everything works, it will be well worth the money and waiting. But it was such a gamble, I wouldn’t dare to play poker with a cosmologist ;-)

  • Questioner

    Secondary Mirror will be deployed in this minute.

  • LocalFulff

    Oh, this is so good! If only the radiator deploys tomorrow, this’ll be alright. Even if the last 1/3 of the mirrors don’t deploy. Even if the L2 orbital insertion doesn’t work. JWST will still make its most important observations, albeit with reduced lifetime and data rate. Tomorrow it will be a functioning telescope.

    And I trust the springs and locks used to deploy the radiator. Humans learned how to fly heavier than air using wires. Already before apes learned how to write, they understood intuitively that if one pulls a wire in one end, the stuff in the other end also moves. Today’s flat screen touchers have become unnecessarily nervous about such things. Space engineers keep it simple. You unfold the umbrella, pull the strings. What could go wrong? How often do you fail to tie your shoes and walk out barefoot?

  • Icepilot

    NASA has been quite reticent regarding the life of Webb, likely for good reasons. I’d guess the error bars extend from not making orbit to flying past.
    But at almost 70, I’m still an optimist (no small feat). Prediction – >20 yrs.

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