401–410 of 522 posts
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JWST, like many other spacecraft, has reaction wheels to orient itself. The reason Kepler ran out of fuel when it did was that it was expending more maneuvering fuel for attitude control because two of its four reaction wheels failed. Hubble and the ISS also had similar failures. We're getting better all the time at building more reliable components (including reaction wheels and cryocoolers) though. Until a few year…
> JWST, like many other spacecraft, has reaction wheels to orient itself. It should be noted that reaction wheels can saturate when the motor reaches its top speed. One then needs to spend fuel to provide a counter-force while the wheel to spins down. So even with reaction wheels running off solar panels or similar you need fuel, though much less.
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It would have lasted a lot longer if its reaction wheels hadn't failed. That was the main failure which shortened its remaining operation.
You'd need at least 3 wheels to orient the craft. I bet that 4 wheels would be able to survive the failure of one.
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> the telescope is aimed at the dark and away from the sun To be more specific; It's "parked" in an orbit [0] that constantly puts Earth between the sun and James Webb. So it's not only aimed away from the sun, Earth is also acting as a planetary scale sunscreen for it. [0] https://en.wikipedia.org/wiki/Lagrange_point
Actually JWST orbits around L2 at appreciable altitude. The unique aspect of the orbit is that it is never in the shadow of the Earth or moon. It guarantees consistent solar power and thermal load. https://jwst-docs.stsci.edu/jwst-observatory-characteristics...
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They have given it a 10 year lifespan. They have said that fuel is a major limiting factor and talked about a refuelling drone to extend life. But I don't think that means it only has 10 years of fuel, and I don't think they have ever said explicitly said that. I suspect it's more like 15 years in the best case. The fact that they aren't already planning a refuelling mission implies that it's not a critical limiting…
Would I be wrong to assume that technological advances in the next 15 years would justify sending a second satellite? As in, instead of a refueling mission we'd be more likely to send a version 2 of the satellite with even better sensors/apparatus/whatnot?
More great news. Congratulations to all who have worked on the project. I understand the reasons for not putting a camera on or near the JWST, but I’m still a little sad that we’ll probably never get to see the thing in situ in all its operational glory. Maybe one day when it finally expires, we can launch a “sample return” mission to tow it back.
Won't it be pretty close to earth in its final position at L2? If so, is there no chance that there will be future missions to do service to it? If so, maybe we can get a photo of if then?
On the other hand, with how delicate the optics and sunshield are, a servicing mission might not be worth it. At that point NASA might find it more productive to build a larger telescope, except this time it could again be designed to be manually deployed and serviced, thus not needing the complex automated deployment that delayed the JWST so much.
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Since L2 is an unstable equilibrium, won’t there also need to be routine adjustments throughout the mission?
Yes. Those adjustments, as well as unloading of the reaction wheels used to position JWST, and the fuel burns reqiured for them, are the principle determinants of the JWAT's lifespan, estimated at 10 years. Nasa have lowballed such estimates for numerous missions in the past (Hubble and numerous Mars lander and rover missions come to mind), and it's possible JWST will exceed the planned lifetime, potentially by a wid…
https://blogs.nasa.gov/webb/2021/12/29/nasa-says-webbs-exces...
I can't help but be a little sad. JWST will be an incredible tool for scientific discovery, but its sensitivity range means it will never produce the kind of compelling imagery that Hubble did. Those pictures played a role in inspiring many of the people in the field today.
I would not be so sure about that. Many (most) astronomy photos are false color photos from quite different wavelength regions (often several different overlayed ones). So I do expect some fascinating images to come out of jwb as well.
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Thus, the "Aft Momentum flap": https://www.jwst.nasa.gov/content/webbLaunch/deploymentExplo...
Momentum flap will bring average CoP closer to CoM but CoP will shift as JWST is rotated to point at different targets. Unwanted torque can be minimised by carefully choosing observations targets so it mostly cancels out but it cannot be done perfectly.
The most exciting idea is if that happens we'll realize they might have built their own version of JWST and proven we exist.