I have not found any information about contingencies for failed wing mirror deployment. Could JWST operate, and at least partially fulfill its scientific mission, with only the center core mirror, containing 12 of the 18 total sections, in case either of the two wings fails to deploy?


1 Answer 1


Q: Could JWST operate with failed or partial wing mirror deployment?

A: Yes.

(but in a limited capacity)

According to this, 15:10:

It can still operate using the light reflecting off of the 12 fixed mirrors.


If worse comes to worst, however, would James Webb still be able to operate if a major mirror system, such as the two foldable wings of the primary mirror, didn’t deploy?

“The only thing I can tell you is that we certainly cannot meet our baseline requirements. Without the wings, we would not meet the requirement for [mirror] area. Where we still could meet a minimal set of requirements is if one mirror does not fully deploy. And we do have contingency plans for what to do if we had an issue, for example, with one of the mirrors.

“For example, we could point the mirror out of the way if we have some actuators working, or we could defocus it. So we could potentially get by without one of the mirrors. I think it’s extremely unlikely that that would happen, though, to be very honest with you. The mirrors have been really well tested, and there’s all the redundancy you would want.”

“The big deployments are different because they are more difficult to test in a 1-g environment. For example, we deployed mirrors during a test at temperature and we deployed them at different gravity orientations. So we’ve really covered all the potential environments. So even though we could live without a mirror, it’s just incredibly unlikely.”


"We can meet all our most fundamental requirements with 17 segments," he said. "We can try to compensate with the other segments and the secondary, it depends on if it's within a certain range. But if it's a bad segment, we can just tilt it completely out of the way with the remaining actuators. That's not great ... but we could still meet our level-one requirements."

  • still looking for more NASA docs though.
  • $\begingroup$ That explicitly says it won't meet its objectives without the big mirror panels. It can get by if just one of the eighteen primary mirrors fails. He also didn't say what would happen in case of an actuator failure on the secondary mirror, and I can't imagine that would be good. $\endgroup$
    – dfeuer
    Jan 7, 2022 at 20:10
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    $\begingroup$ I know, that's why I am still looking but wanted to put down what I had read thus far. The youtube video seems to be the only one so far that explicitly states it will still work with just the fixed mirrors. The NASA quotes appear to be in the negative without explicitly saying 'its a bust'. I included them as specific 'what if it (PM wings) doesn't work' is not often addressed. What I was looking for was what should happen if the Wing Deployment Hinge failed. Most other material states that all 18 mirrors are required for accurate readings. $\endgroup$ Jan 7, 2022 at 20:33
  • $\begingroup$ Yeah. I would imagine they'd still get a telescope, albeit not a great one. I was particularly nervous about the secondary mirror deployment, because failure there would be an automatic no-telescope scenario. $\endgroup$
    – dfeuer
    Jan 7, 2022 at 21:13
  • $\begingroup$ thats right, the SM failure would definitely mean the whole thing has bought the farm. No talking out of that one. $\endgroup$ Jan 7, 2022 at 21:25
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    $\begingroup$ Great answer and ongoing effort to find more sources! Note that the OP asks only: "Could JWST operate... and at least partially fulfill its scientific mission... with failed or partial wing mirror deployment?" In addition to the focus on meeting their "level-one requirements" it might be good to also address if it would still be a kick-ass and incredibly useful space telescope. It sounds like it would. It would have a fraction less area and a larger point spread function (diffraction pattern). $\endgroup$
    – uhoh
    Jan 7, 2022 at 21:46

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