I think, if something does not work (had not worked), or some improvisative solution is needed to handle an unexpected problem, then it would significantly improve the configuration freedom if the deployment steps could be reverted. For example, if something opens only partially, then it seems viable to first close it and then issue a complete re-open command.

Can JWST do it?

  • 2
    $\begingroup$ nope. Most of the deployment was in the form of released spring-loaded systems, motors winching in cable, etc. They were reversible only using external input, as seen in the many deployment-test videos. $\endgroup$ Commented Jan 11, 2022 at 12:27
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    $\begingroup$ If something fails, it not reasonable to assume reverting the same step would actually work. It could, in fact, make things even worse. $\endgroup$
    – Polygnome
    Commented Jan 11, 2022 at 13:30
  • $\begingroup$ @Polygnome I don't think it so, and exactly the half-opened things are my best example. $\endgroup$
    – peterh
    Commented Jan 11, 2022 at 20:58

1 Answer 1


No. With only a few, rare exceptions, deployments are one-time events. When they are tested on the ground, people manually push the hardware back into the stowed position and reset the lock-down devices.

  • $\begingroup$ I heard that was true for the "aft trim tab". And I can't imagine re-folding the sunshield. But are there any components which can be reverted? $\endgroup$
    – Woody
    Commented Jan 15, 2022 at 4:46
  • $\begingroup$ Your answer would be improved by adding some links/resources backing up what your're saying. $\endgroup$
    – Freddie R
    Commented Jan 16, 2022 at 21:24
  • $\begingroup$ Question for Freddie R: I worked on spacecraft for 35 years, and I based my answer on what is common knowledge in the industry. Finding links to common knowledge is problematic. How would you suggest I proceed? $\endgroup$ Commented Jan 18, 2022 at 20:00
  • $\begingroup$ Reply to Woody: I would expect the aft trim tab has some range of motion after it is deployed. Its function is to balance out the solar sunlight pressure, and that may change as the sunshield ages or with the spacecraft attitude. To balance those changing torques, I'd think the trim tab can be moved by perhaps some 10s of degrees. But I'd be surprised if they could retract it all the way to the stowed position and lock it in place - because I can't see a need to do so, and spacecraft don't include features they don't need. However, I'm speculating based on my experience, not design documents. $\endgroup$ Commented Jan 18, 2022 at 20:07

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