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Old 19th October 2021, 06:12 AM   #121
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Looks like 6 months+ until deployment and testing is complete and the mission begins:

https://webbtelescope.org/contents/m...ges/4180-Image
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Old 19th October 2021, 06:13 AM   #122
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Originally Posted by 3point14 View Post
Forgive my ignorance. And this is probably in the thread somewhere.

How long does it take to get on station and then start working? When can we expect pictures of little green men?
We already have them. Had them for years. But there is a big government conspiracy to keep them from the general public, don't you know. (and they are actually sort of a greenish-grey color)
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Old 19th October 2021, 06:36 AM   #123
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Don't worry about what might be in the thread earlier. It might be wrong by now. June-ish is when the first real images are expected to show up. Possible other calibration images might get released before then. It takes a month just to get to where it's going to deploy.

ETA: Sneaky 4th page.

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Old 19th October 2021, 06:48 AM   #124
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Originally Posted by 3point14 View Post
Forgive my ignorance. And this is probably in the thread somewhere.

How long does it take to get on station and then start working? When can we expect pictures of little green men?
Originally Posted by ohms View Post
Looks like 6 months+ until deployment and testing is complete and the mission begins:

https://webbtelescope.org/contents/m...ges/4180-Image
Cool info.
Quote:
An Ariane-5 rocket will throw the telescope out to an observing position about 1.5 million km from Earth.
That's farther away than the moon, by the way, which is only 384,400 km away.

Presumably if there are any serious problems, we would learn about them before six months into the mission.
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Old 24th October 2021, 11:54 PM   #125
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IIRC once it's in its way there is nothing we can do to fix it.
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Old 25th October 2021, 12:24 AM   #126
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Originally Posted by a_unique_person View Post
IIRC once it's in its way there is nothing we can do to fix it.
I bet Elon would try.
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Old 25th October 2021, 06:46 AM   #127
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Originally Posted by a_unique_person View Post
IIRC once it's in its way there is nothing we can do to fix it.
It would be far-fetched. Maybe not impossible, but certainly not easy.

It will be about 4 times farther away from earth than the moon. No human has ever gone out that far from earth, have they? The far side of the moon is the farthest away we've been, unless I'm mistaken. Just getting out that far would take nearly a month.
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Old 25th October 2021, 07:01 AM   #128
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No human has ever been to the far side of the Moon.

ETA: Wait. You probably mean just distance? Yeah, just the other side of the Moon. No manned mission landed on the far side.

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Old 25th October 2021, 07:11 AM   #129
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Originally Posted by Puppycow View Post
It would be far-fetched. Maybe not impossible, but certainly not easy.

It will be about 4 times farther away from earth than the moon. No human has ever gone out that far from earth, have they? The far side of the moon is the farthest away we've been, unless I'm mistaken. Just getting out that far would take nearly a month.
You could get there a lot faster if you wanted to. The problem, though, is that you would be going faster, which means you'd have to spend a lot of energy to STOP there. So it's actually better to get there slower.
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Old 25th October 2021, 08:16 AM   #130
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Originally Posted by RecoveringYuppy View Post
No human has ever been to the far side of the Moon.

ETA: Wait. You probably mean just distance? Yeah, just the other side of the Moon. No manned mission landed on the far side.
I just meant in orbit around the moon, which meant going around the far side.

Originally Posted by Ziggurat View Post
You could get there a lot faster if you wanted to. The problem, though, is that you would be going faster, which means you'd have to spend a lot of energy to STOP there. So it's actually better to get there slower.
Also there's no moon there to help you change directions. Then you of course need to match speeds with the telescope, and then come back home again. All of which require more fuel.
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Old 25th October 2021, 08:30 AM   #131
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If you're heading to the telescope, your braking burns would have to be pointed more or less at the telescope. I wonder if the outgassing would cause problems for the telescope.
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Old 25th October 2021, 09:36 AM   #132
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Originally Posted by theprestige View Post
If you're heading to the telescope, your braking burns would have to be pointed more or less at the telescope. I wonder if the outgassing would cause problems for the telescope.
You can use sets of angled jets, so the jets don't point directly at the target you approach, but a bit to the side. I think that's already the case for the capsules that dock with the ISS.
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Old 25th October 2021, 11:05 AM   #133
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I suspect the manned rescue mission would cost more than just building and launching another telescope.
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Old 25th October 2021, 11:15 AM   #134
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But would it take as long? It began development in 1996 for a 2007 launch.
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Old 25th October 2021, 03:20 PM   #135
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Let's just hope this one works. If it doesn't, they'll probably go back to the drawing boards. There won't be a rescue mission, and they won't build another one just like it.
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Old 25th October 2021, 03:56 PM   #136
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I wonder if you could get odds from someone on the possibility that Hubble is still doing science when JWT is done.
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Old 25th October 2021, 05:59 PM   #137
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Originally Posted by BowlOfRed View Post
I wonder if you could get odds from someone on the possibility that Hubble is still doing science when JWT is done.
Sure. Not me, but it's absolutely within the realm of possibility. If for no other reason than that it's not a sure thing that the JWST will ever work in the first place. But if everything goes according to plan, and it does work, I don't see why it shouldn't keep working for a long time.
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Old 25th October 2021, 06:37 PM   #138
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To me, it seems like the biggest risk is the deployment process. All those moving parts. If that goes well, the next biggest risk is miscalculation of the heat load and heat dumping. If those numbers are even a little bit wrong, JWST is probably doomed.

So I guess we'll see.
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Old 25th October 2021, 08:29 PM   #139
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Originally Posted by BowlOfRed View Post
I wonder if you could get odds from someone on the possibility that Hubble is still doing science when JWT is done.
JWT's initial mission is for five years, and might last ten. Eventually it will run out of fuel for station-keeping.

Now keep in mind that Hubble was designed to be serviced using the Space Shuttle; it's one of the reasons it's lasted so long. Now that the shuttles are no longer flying, as things on Hubble break they won't get fixed. Eventually something critical will go and NASA will have to de-orbit the telescope.

In my opinion, I think the Hubble will fail before the James Webb telescope does, provided of course the JWST deploys as expected. I'd be happy to be wrong, though. (See: Voyager)
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Old 25th October 2021, 11:19 PM   #140
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Originally Posted by Puppycow View Post
Sure. Not me, but it's absolutely within the realm of possibility. If for no other reason than that it's not a sure thing that the JWST will ever work in the first place. But if everything goes according to plan, and it does work, I don't see why it shouldn't keep working for a long time.
Because JWST requires fuel for stationkeeping. It requires consumables to be useful, and the design lifetime for them is 10 years.

Admittedly, they would be long odds (Hubble has had several issues and eventually one of the failures will kill it). But the long tail of survivability for HST does reach to around 2040. I suspect that JWST fuel usage will end up being below the estimates, but reaching 2040 would be a stretch as well.
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Old 28th October 2021, 04:21 AM   #141
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An interesting read plus other interesting links.

https://news.ucsc.edu/2021/10/jwst-launch.html

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Old 28th October 2021, 05:27 AM   #142
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Originally Posted by BowlOfRed View Post
Because JWST requires fuel for stationkeeping. It requires consumables to be useful, and the design lifetime for them is 10 years.

Admittedly, they would be long odds (Hubble has had several issues and eventually one of the failures will kill it). But the long tail of survivability for HST does reach to around 2040. I suspect that JWST fuel usage will end up being below the estimates, but reaching 2040 would be a stretch as well.
I see.

Although if recent experience is any guide, some NASA missions go on well past their planned duration. So we'll see. If they try to be as efficient as possible with the fuel use, maybe they can make it stretch longer.
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Old 29th October 2021, 09:43 AM   #143
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Isnít it normally coolant that is the limiting factor? As far as I remember coolant tends to run out faster than expected.
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Old 29th October 2021, 10:18 AM   #144
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Originally Posted by steenkh View Post
Isn’t it normally coolant that is the limiting factor? As far as I remember coolant tends to run out faster than expected.
Depends on the telescope and the design. Spitzer had two instruments that needed very cold temperatures and used evaporative helium cooling. Simple in concept, but makes it a consumable. 350l of helium lasted ~5.5 years (which was beyond the 5 year design). Also, most telescopes in earth orbit need some means to control attitude, but don't need propellent to hold station.

JWST has a design temperature of 40K, but is supposed to achieve that with passive cooling thanks to the big sun shield. That will be sufficient for 3 of the instruments.

There is a fourth instrument that needs 7K to operate. It will come with (what I think is) a newish cooler. It uses helium as the working fluid, but is a closed system, not evaporative. Unless something breaks, there's no expectation that the coolant will reduce over time.
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Old 29th October 2021, 11:22 AM   #145
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Originally Posted by steenkh View Post
Isn’t it normally coolant that is the limiting factor? As far as I remember coolant tends to run out faster than expected.
The primary mirror is cooled by being exposed to space, with an incredibly efficient five-layer heat shield between it and the Sun/Earth system. Being at the L2 Lagrange point, the telescope, the Earth, and the Sun are all in a line.

One instrument on the JWST, the MIRI (Mid-InfraRed Instrument) uses a a helium gas mechanical cooler (see Cryocooler on Wikipedia.) I don't know the expected lifespan on this piece of equipment.


ETA: Ninja'd by Bowl of Red!
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Old 29th October 2021, 04:42 PM   #146
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Thanks, it sounds reassuring.
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Old 29th October 2021, 04:50 PM   #147
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I knew NASA was responsible for the design, but I had some doubts they would think it through and do it right, until someone on the internet told me a plausible tale of potential competence. "Sounds reassuring" my ass.
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Old 29th October 2021, 10:02 PM   #148
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Originally Posted by theprestige View Post
I knew NASA was responsible for the design, but I had some doubts they would think it through and do it right, until someone on the internet told me a plausible tale of potential competence. "Sounds reassuring" my ass.
"I thought the lifetime of this telescope might be limited by the need to supply coolant that could be used up over time until someone on the internet explained to me that this isn't actually a design constraint."

Not seeing anything unreasonable there at all. There's no implied incompetence if coolant was going to be used up over time, so why you think there was any implication of NASA's incompetence in the worry escapes me.
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Old 29th October 2021, 11:38 PM   #149
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Originally Posted by Roboramma View Post
"I thought the lifetime of this telescope might be limited by the need to supply coolant that could be used up over time until someone on the internet explained to me that this isn't actually a design constraint."

Not seeing anything unreasonable there at all. There's no implied incompetence if coolant was going to be used up over time, so why you think there was any implication of NASA's incompetence in the worry escapes me.
Thanks, Roboramma. You are right, I didnít think of the coolant restraint as being a sign of incompetence, but merely as a design constraint. Now I know that the design has removed this constraint entirely, and that is reassuring.

I do have other worries about the JWT. Some years ago there was an article in Sky & Telescope about how every major telescope had had design flaws that needed to be fixed afterwards, and that included the HST. I note that the HST is not the only major space telescope, so the article was definitely wrong, but I do see how so much more can go wrong with the JWT than with any previous telescope.

But if anybody can get it right, NASA can.
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Old 30th October 2021, 04:39 AM   #150
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Originally Posted by steenkh View Post
I do have other worries about the JWT. Some years ago there was an article in Sky & Telescope about how every major telescope had had design flaws that needed to be fixed afterwards, and that included the HST. I note that the HST is not the only major space telescope, so the article was definitely wrong, but I do see how so much more can go wrong with the JWT than with any previous telescope.

But if anybody can get it right, NASA can.
The HST absolutely had a major design flaw. Or perhaps it was a manufacturing flaw.

https://en.wikipedia.org/wiki/Hubble...#Flawed_mirror

Quote:
Analysis of the flawed images revealed that the primary mirror had been polished to the wrong shape. Although it was believed to be one of the most precisely figured optical mirrors ever made, smooth to about 10 nanometers,[27] the outer perimeter was too flat by about 2200 nanometers (about 1⁄450 mm or 1⁄11000 inch).[64] This difference was catastrophic, introducing severe spherical aberration, a flaw in which light reflecting off the edge of a mirror focuses on a different point from the light reflecting off its center.[65]
Quote:
A commission headed by Lew Allen, director of the Jet Propulsion Laboratory, was established to determine how the error could have arisen. The Allen Commission found that a reflective null corrector, a testing device used to achieve a properly shaped non-spherical mirror, had been incorrectly assembled—one lens was out of position by 1.3 mm (0.051 in).[70] During the initial grinding and polishing of the mirror, Perkin-Elmer analyzed its surface with two conventional refractive null correctors. However, for the final manufacturing step (figuring), they switched to the custom-built reflective null corrector, designed explicitly to meet very strict tolerances. The incorrect assembly of this device resulted in the mirror being ground very precisely but to the wrong shape. A few final tests, using the conventional null correctors, correctly reported spherical aberration. But these results were dismissed, thus missing the opportunity to catch the error, because the reflective null corrector was considered more accurate.[71]

The commission blamed the failings primarily on Perkin-Elmer. Relations between NASA and the optics company had been severely strained during the telescope construction, due to frequent schedule slippage and cost overruns. NASA found that Perkin-Elmer did not review or supervise the mirror construction adequately, did not assign its best optical scientists to the project (as it had for the prototype), and in particular did not involve the optical designers in the construction and verification of the mirror. While the commission heavily criticized Perkin-Elmer for these managerial failings, NASA was also criticized for not picking up on the quality control shortcomings, such as relying totally on test results from a single instrument.[72]
Hopefully the lessons from that episode were learned and won't be repeated with the JWST.
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Old 30th October 2021, 07:51 AM   #151
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Originally Posted by steenkh View Post
I note that the HST is not the only major space telescope, so the article was definitely wrong, but I do see how so much more can go wrong with the JWT than with any previous telescope.
This sentence confused me and maybe the poster ahead of me. It doesn't seem to follow or explain what you wrote before it.
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Old 30th October 2021, 10:42 AM   #152
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Originally Posted by RecoveringYuppy View Post
This sentence confused me and maybe the poster ahead of me. It doesn't seem to follow or explain what you wrote before it.

Sorry about that. The original article had a list of big telescopes, and how they had to be repaired after they were declared ready. The problems were not just about optics, but also the mount and the foundation.

When I look at at the JWT, I see a complicated process of launching, unfurling, and so on, and I worried about each of these steps that could end a disaster.

That was all I meant.
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Old 23rd November 2021, 09:32 AM   #153
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Old 23rd November 2021, 10:47 AM   #154
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Gosh, I hope they didn't damage it.

https://arstechnica.com/science/2021...-has-occurred/

Quote:
"Technicians were preparing to attach Webb to the launch vehicle adapter, which is used to integrate the observatory with the upper stage of the Ariane 5 rocket," NASA said in a blog post. "A sudden, unplanned release of a clamp band—which secures Webb to the launch vehicle adapter—caused a vibration throughout the observatory."

Let's be honest, words like "incident," "sudden," and "vibration" are not the kinds of expressions one wants to hear about the handling of a delicate and virtually irreplaceable instrument like the Webb telescope. However, NASA, the European Space Agency, and the rocket's operator, Arianespace, have a plan for moving forward.
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Old 23rd November 2021, 11:21 PM   #155
Samson
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Originally Posted by Puppycow View Post
Gosh, I hope they didn't damage it.

https://arstechnica.com/science/2021...-has-occurred/
Unfortunately
"What could possibly go wrong?"

Is doing my head in.
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Old 25th November 2021, 03:15 AM   #156
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Looks like they are good to go on the 22nd:

https://blogs.nasa.gov/webb/2021/11/...dec-22-launch/
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Old 25th November 2021, 05:42 AM   #157
Darat
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Originally Posted by Puppycow View Post
Gosh, I hope they didn't damage it.

https://arstechnica.com/science/2021...-has-occurred/
....have a plan for moving forward......






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