James Webb Space Telescope Secondary Mirror Deployment Confirmed
NASA James Webb Space Telescope Mission Update
Jan. 5, 2022
Today, Webb teams successfully deployed the observatory’s secondary mirror support structure. When light from the distant universe hits Webb’s iconic 18 gold primary mirrors, it will reflect off and hit the smaller, 2.4-foot (.74-meter) secondary mirror, which will direct the light into its instruments. The secondary mirror is supported by three lightweight deployable struts that are each almost 25 feet long and are designed to withstand the space environment. Specialized heating systems were used to warm up the joints and motors needed for seamless operation.
“Another banner day for JWST,” said Bill Ochs, Webb project manager at NASA’s Goddard Space Flight Center, as he congratulated the secondary mirror deployment team at the Mission Operations Center in Baltimore. “This is unbelievable…We’re about 600,000 miles from Earth, and we actually have a telescope.”
The deployment process began at approximately 9:52 a.m. EST, and the secondary mirror finished moving into its extended position at about 11:28 a.m. EST. The secondary mirror support structure was then latched at about 11:51 a.m. EST. At approximately 12:23 p.m. EST, engineers confirmed that the structure was fully secured and locked into place and the deployment was complete.
“The world’s most sophisticated tripod has deployed,” said Lee Feinberg, optical telescope element manager for Webb at Goddard. “That’s really the way one can think of it. Webb’s secondary mirror had to deploy in microgravity, and in extremely cold temperatures, and it ultimately had to work the first time without error. It also had to deploy, position, and lock itself into place to a tolerance of about one and a half millimeters, and then it has to stay extremely stable while the telescope points to different places in the sky – and that’s all for a secondary mirror support structure that is over 7 meters in length.”
Next Webb will deploy an important radiator system known as the aft deployable infrared radiator (ADIR), which helps shed heat away from its instruments and mirrors. Learn more about Webb’s deployment timeline online.
4 responses to “James Webb Space Telescope Secondary Mirror Deployment Confirmed”
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Interesting comment today from program manager Bill Ochs as he congratulated the team after the secondary mirror deployment. He said, “We are about 600,000 miles from Earth and we actually have a telescope”.
Now that the sunshade and the secondary mirror have been deployed, and with twelve of the eighteen primary mirror segments already in position, technically the telescope could do science even if the other six segments are not deployed. Obviously losing one-third of its light gathering capacity would greatly reduce Webb’s capability, but I wonder how much of that could be made up with longer exposures? Or would there be other problems to deal with besides receiving less light?
That’s been my thought — as long as the secondary is out there, and given that the sun shield is already deployed, you at least have a partial mission to work with. Basically, even a partial primary can reflect some light to the secondary mirror, which can then in turn redirect that light to the instruments (perhaps via a tertiary mirror and other possible turns of the light once it passes through the central hole in the primary).
Of course the individual mirror segments on the main telescope and the secondary have to be actuated and coordinated, but assuming all those actuators work well, I think they’d be able to come up with algorithmic compensations for having a non-circular primary of reduced aperture. Obviously it wouldn’t be ideal, but it might still beat any existing or previous IR telescope, especially in the central portion of the image field. In particular, I would guess that spectroscopy would still work well for the relatively brighter targets.
Well, I’m no optics expert, so that’s mostly just speculating. But as an amateur astronomer, I do know that damaged optics can still work surprisingly well (surprisingly well compared to how one might think they wouldn’t work at all or would be just absolutely terrible; but on the other hand, no, a damaged mirror isn’t going to achieve the $10 billion level of perfection they they’ve been going for here).
Andrew, what say you?
One of our company expressions is that “perfection is an illusion of a limited mind”*. Meaning that perfection assumes there is no room for improvement anywhere. I’ve never done a perfect construction job that couldn’t have been improved in some manner. Quality, price, service, missed opportunity in design etc.
* other expressions
“waste a dollar and it takes friends with it when it leaves home, and it won’t even send you a post card telling you what a good time its’ having”
“do you want it done right or done your way?”
“if the customer was always right, he wouldn’t need us to do it for him”
Another post that if I could like it 10,000 times, I would. Well said!
Or as the Russians say “perfection is the enemy of good enough”.