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The James Webb Space Telescope has passed the final mission analysis review

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Re: The James Webb Space Telescope has passed the final mission analysis review

#241

Post by jasonwatkinspdx »

caconym_ wrote: post #229
jasonwatkinspdx wrote: post #226

Earlier quoted context omitted.

I know where SpaceX is. Elon does have a clear history of being overly optimistic about timelines. There's a zero percent chance they'll have a vehicle ready by the JWT launch date that could launch it instead, even if they get to orbit by then. This is not a race. As I said I'm a SpaceX fan, but I am not a fan of every single space topic being derailed by "but what about SpaceX?" as if they're the only company doing…

> I know where SpaceX is. I mean, Musk may be famous for his "optimistic" timelines, but you completely misrepresented their progress. "Still trying to get hovering grain silo versions working" is not remotely accurate. That's the only point of my previous comment: give credit where it's due, as I said. I agree with most or all of the other things you've said in this subthread.

I am giving credit. I'll call it working when they've demonstrated repeated access to orbit. Until they, they are indeed playing with flying grain silo prototypes, even if they landed one belly flop maneuver.

In any case, this is the exact sort of argument I find entirely wasteful of energy, and a distraction from what we should be talking about in this thread, which is JWT.

Re: The James Webb Space Telescope has passed the final mission analysis review

#242

Post by marcyb5st »

boardwaalk wrote: post #222
manquer wrote: post #210

Earlier quoted context omitted.

The challenges in building a mirror that size is enormous and take years. It is not only fairing size that is limiting

Wouldn't land-based telescopes already use larger mirrors than any space telescope?

Yes they do, but you have to consider the problems that the atmosphere poses. A lot of the budget for ground telescopes goes into the adaptive optics (actuators that can deform the mirror to compensate for distortions due to non-uniform column of air above the telescope). For adaptive optics to be effective you need bigger mirrors because you can't deform a small mirror enough to counter that.

Additionally, the atmosphere blocks a bunch of wavelengths that are really interesting to observe [1] so we still want to be in space for these observations.

Finally, in the non distant future I believe space telescopes will ditch mirrors altogether. For instance, the proposed Aragoscope [2] would use diffraction optics instead of so called geometric optics (lenses, mirrors) to focus light. Since the material that can provide the diffraction can be anything it would be much cheaper to launch a sheet of that can unfold once in space instead of incredibly precise and fragile mirrors. Also, according to Nasa, this approach can achieve ~1000 time the resolution of HST at a fraction of the price and we are only limited by the size of the disk creating the diffraction.

[1] https://www.researchgate.net/figure/The-atmospheric-transmis... .

[2] https://www.nasa.gov/content/the-aragoscope-ultra-high-resol... .

Re: The James Webb Space Telescope has passed the final mission analysis review

#243

Post by nine_k »

imglorp wrote: post #214
nine_k wrote: post #203

Earlier quoted context omitted.

As already said, the problem is in coordination of multiple telescopes in spacetime. It might be better to build one giant telescope piecemeal, by adding more and more small mirrors. A similar approach is taken by several terrestrial telescopes. It would still be very interesting to have a few space telescopes distributed across the Solar system, much wider than the Earth orbit. It could give a sort of stereoscopic p…

Actually, pulsars can be used for timing and position, and all telescopes in your fleet could have sight of the same ones. It's probably far easier to do interferometry if you don't have atmospheric distortion to deal with.

Accordung to the theory of relativity, there's no such thing as "the same moment" between two distant bodies. When the distance is light milliseconds, we can pretend it does not exist. When it is light-seconds, like between Earth and GEO, it becomes hard to ignore. With many light hours which would separate the telescopes I was talking about, the idea of "the same moment" just becomes nonsensical, even in very approximate household terms.

Such telescopes could, of course, register the same compact body, like an exoplanet, and then their pictures could be put together on one timeline, the planet's, thus synchronized.

Maybe if a pulsar happens to be close (in angular terms) to the object observed, it could help synchronize the pictures. If the pulsar lies in a seriously different direction, it likely would be less helpful: most pulsars have rather short periods, and all pulses are the same.

Re: The James Webb Space Telescope has passed the final mission analysis review

#244

Post by Rebelgecko »

imglorp wrote: post #214
nine_k wrote: post #203

Earlier quoted context omitted.

As already said, the problem is in coordination of multiple telescopes in spacetime. It might be better to build one giant telescope piecemeal, by adding more and more small mirrors. A similar approach is taken by several terrestrial telescopes. It would still be very interesting to have a few space telescopes distributed across the Solar system, much wider than the Earth orbit. It could give a sort of stereoscopic p…

Actually, pulsars can be used for timing and position, and all telescopes in your fleet could have sight of the same ones. It's probably far easier to do interferometry if you don't have atmospheric distortion to deal with.

OTOH it's much harder to do interferometry when you aren't able to sit on the ground and be stable: your refrigeration units can't be located somewhere far away to reduce vibration, and you can't stationkeep with nanometer accuracy (which may or may not matter depending on your frequency- in the past space based interferometry has usually only been practical for very long wavelengths)

Re: The James Webb Space Telescope has passed the final mission analysis review

#245

Post by Taniwha »

foolfoolz wrote: post #237
zabzonk wrote: post #221

Earlier quoted context omitted.

> Instead of building one huge short life-span spacecraft Short life-span? How long has the Hubble been up there?

webb needs to use thrusters to stay in position. there’s 5 years worth of fuel onboard they did design the fuel in a way that potentially could be refilled… but the refilling craft doesn’t exist. and webb timescales make that sound impossible

And it's at L2 so not that easy to get to

Re: The James Webb Space Telescope has passed the final mission analysis review

#246

Post by Rebelgecko »

justshowpost wrote: post #158
RapidFire wrote: post #147

Earlier quoted context omitted.

Thanks for this comment; that's a fascinating bit of information.

But that was just like saying what F-35's mission is to fly high in the skies , sorry. This sort of proves my point, no one knows which exactly research JWST will do upon deployment, because original mission goals mainly became obsolete.

>This sort of proves my point, no one knows which exactly research JWST will do upon deployment

The research isn't a secret, JWST is already booked solid for like 18 months after it launches. You can see how that time is allocated across various projects here: https://www.stsci.edu/jwst/science-execution/approved-progra...

Re: The James Webb Space Telescope has passed the final mission analysis review

#247

Post by caconym_ »

jasonwatkinspdx wrote: post #241
caconym_ wrote: post #229

Earlier quoted context omitted.

> I know where SpaceX is. I mean, Musk may be famous for his "optimistic" timelines, but you completely misrepresented their progress. "Still trying to get hovering grain silo versions working" is not remotely accurate. That's the only point of my previous comment: give credit where it's due, as I said. I agree with most or all of the other things you've said in this subthread.

I am giving credit. I'll call it working when they've demonstrated repeated access to orbit. Until they, they are indeed playing with flying grain silo prototypes, even if they landed one belly flop maneuver. In any case, this is the exact sort of argument I find entirely wasteful of energy, and a distraction from what we should be talking about in this thread, which is JWT.

> I am giving credit.

No, you aren't. "Still trying to get hovering grain silo versions working" is not an accurate characterization of the current state of Starship development: they had hovering in the bag months ago, and have since demonstrated much more challenging and impressive capabilities.

> I'll call it working when they've demonstrated repeated access to orbit. Until they, they are indeed playing with flying grain silo prototypes, even if they landed one belly flop maneuver.

None of this is germane to the problems with your original statement. It's just empty snark--if you want to call rockets "grain silos", I'm not going to try to stop you, though I might caution you against erasing your ability to identify actual silos full of grain.

> In any case, this is the exact sort of argument I find entirely wasteful of energy, and a distraction from what we should be talking about in this thread, which is JWT.

I'm just here to correct the record, which I think is reasonable as there's a lot of weird SpaceX misinformation out there, both "for" and "against". Personally I don't understand why people can't just sit back and watch what happens, without putting their own spin on it.

Re: The James Webb Space Telescope has passed the final mission analysis review

#249

Post by prox »

Taniwha wrote: post #245
foolfoolz wrote: post #237

Earlier quoted context omitted.

webb needs to use thrusters to stay in position. there’s 5 years worth of fuel onboard they did design the fuel in a way that potentially could be refilled… but the refilling craft doesn’t exist. and webb timescales make that sound impossible

And it's at L2 so not that easy to get to

I take Starship could, and should be operational in some form by then.

Re: The James Webb Space Telescope has passed the final mission analysis review

#250

Post by prox »

spaetzleesser wrote: post #139

When I look at project management for the small projects (1-20 people) I am working on I always wonder how projects of such a complexity are managed. It must be freakishly difficult to coordinate all the pieces. The people working on this will also have several stressful months ahead of them. From launch to full deployment so many things can go wrong and there is nothing that can be done when something fails.

I followed their account, the last few years have been test after test after test.
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