James Webb Telescope - Page 4

ohms · 19th October 2021, 06:12 AM

Looks like 6 months+ until deployment and testing is complete and the mission begins:

https://webbtelescope.org/contents/m...ges/4180-Image

Steve · 19th October 2021, 06:13 AM

Originally Posted by 3point14

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)

RecoveringYuppy · 19th October 2021, 06:36 AM

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.

Puppycow · 19th October 2021, 06:48 AM

Originally Posted by 3point14

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

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.

a_unique_person · 24th October 2021, 11:54 PM

IIRC once it's in its way there is nothing we can do to fix it.

arthwollipot · 25th October 2021, 12:24 AM

Originally Posted by a_unique_person

IIRC once it's in its way there is nothing we can do to fix it.

I bet Elon would try.

Puppycow · 25th October 2021, 06:46 AM

Originally Posted by a_unique_person

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.

RecoveringYuppy · 25th October 2021, 07:01 AM

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.

Ziggurat · 25th October 2021, 07:11 AM

Originally Posted by Puppycow

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.

Puppycow · 25th October 2021, 08:16 AM

Originally Posted by RecoveringYuppy

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

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.

theprestige · 25th October 2021, 08:30 AM

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.

Ziggurat · 25th October 2021, 09:36 AM

Originally Posted by theprestige

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.

Myriad · 25th October 2021, 11:05 AM

I suspect the manned rescue mission would cost more than just building and launching another telescope.

Trebuchet · 25th October 2021, 11:15 AM

But would it take as long? It began development in 1996 for a 2007 launch.

Puppycow · 25th October 2021, 03:20 PM

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.

BowlOfRed · 25th October 2021, 03:56 PM

I wonder if you could get odds from someone on the possibility that Hubble is still doing science when JWT is done.

Puppycow · 25th October 2021, 05:59 PM

Originally Posted by BowlOfRed

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.

theprestige · 25th October 2021, 06:37 PM

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.

Blue Mountain · 25th October 2021, 08:29 PM

Originally Posted by BowlOfRed

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)

BowlOfRed · 25th October 2021, 11:19 PM

Originally Posted by Puppycow

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.

Steve001 · 28th October 2021, 04:21 AM

Scheduled launch date December 18th 2021
An interesting read plus other interesting links.

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

Puppycow · 28th October 2021, 05:27 AM

Originally Posted by BowlOfRed

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.

steenkh · 29th October 2021, 09:43 AM

Isn’t it normally coolant that is the limiting factor? As far as I remember coolant tends to run out faster than expected.

BowlOfRed · 29th October 2021, 10:18 AM

Originally Posted by steenkh

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.

Blue Mountain · 29th October 2021, 11:22 AM

Originally Posted by steenkh

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!

steenkh · 29th October 2021, 04:42 PM

Thanks, it sounds reassuring.

theprestige · 29th October 2021, 04:50 PM

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.

Roboramma · 29th October 2021, 10:02 PM

Originally Posted by theprestige

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.

steenkh · 29th October 2021, 11:38 PM

Originally Posted by Roboramma

"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 didn’t 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.

Puppycow · 30th October 2021, 04:39 AM

Originally Posted by steenkh

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.

RecoveringYuppy · 30th October 2021, 07:51 AM

Originally Posted by steenkh

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.

steenkh · 30th October 2021, 10:42 AM

Originally Posted by RecoveringYuppy

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.

wobs · 23rd November 2021, 09:32 AM

Delayed to the 22nd Dec:
https://www.space.com/james-webb-spa...ay-december-22

Puppycow · 23rd November 2021, 10:47 AM

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.

Samson · 23rd November 2021, 11:21 PM

Originally Posted by Puppycow

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.

ohms · 25th November 2021, 03:15 AM

Looks like they are good to go on the 22nd:

https://blogs.nasa.gov/webb/2021/11/...dec-22-launch/

Darat · 25th November 2021, 05:42 AM

Originally Posted by Puppycow

Gosh, I hope they didn't damage it.

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

....have a plan for moving forward......

Samson · 4th December 2021, 02:12 AM

Here is a remarkable interview to enjoy.
Complex to the end.

https://www.rnz.co.nz/national/progr...cope-to-launch

Also, things that hurt when you drop them on your foot (protons etc) are apparently down to 1% of the universe.
Whut??

Puppycow · 11th December 2021, 04:23 AM

YouTube Video This video is not hosted by the ISF. The ISF can not be held responsible for the suitability or legality of this material. By clicking the link below you agree to view content from an external website.

I AGREE

Gord_in_Toronto · 13th December 2021, 08:02 PM

World’s most powerful space telescope will let researchers look back in time. This Canadian astronomer will be among its first users

https://www.thestar.com/news/canada/...rst-users.html

Quote:

Of the nearly 1,200 proposals received from 44 countries around the world, only 286 had been selected for time on the JWST, and only 10 of those with Canadians as principal investigators.

Quite a good description of the project too.

19th October 2021, 06:12 AM	#121
ohms Graduate Poster Join Date: Apr 2005 Posts: 1,450	Looks like 6 months+ until deployment and testing is complete and the mission begins: https://webbtelescope.org/contents/m...ges/4180-Image
ohms Graduate Poster Join Date: Apr 2005 Posts: 1,450	__________________ Long time lurker

19th October 2021, 06:13 AM	#122
Steve Penultimate Amazing Join Date: May 2005 Location: Sydney Nova Scotia Posts: 11,432	Originally Posted by 3point14 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)
	__________________ Caption from and old New Yorker cartoon - Why am I shouting? Because I'm wrong!"

19th October 2021, 06:36 AM	#123
RecoveringYuppy Penultimate Amazing Join Date: Nov 2006 Posts: 13,591	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.
	Last edited by RecoveringYuppy; 19th October 2021 at 06:38 AM.

19th October 2021, 06:48 AM	#124
Puppycow Penultimate Amazing Join Date: Jan 2003 Location: Yokohama, Japan Posts: 27,262	Originally Posted by 3point14 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 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.
	__________________ A fool thinks himself to be wise, but a wise man knows himself to be a fool. William Shakespeare

24th October 2021, 11:54 PM	#125
a_unique_person Director of Hatcheries and Conditioning Join Date: Jul 2002 Location: Waiting for the pod bay door to open. Posts: 44,460	IIRC once it's in its way there is nothing we can do to fix it.
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25th October 2021, 12:24 AM	#126
arthwollipot Observer of Phenomena Pronouns: he/him Join Date: Feb 2005 Location: Ngunnawal Country Posts: 77,485	Originally Posted by a_unique_person 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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25th October 2021, 06:46 AM	#127
Puppycow Penultimate Amazing Join Date: Jan 2003 Location: Yokohama, Japan Posts: 27,262	Originally Posted by a_unique_person 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.
	__________________ A fool thinks himself to be wise, but a wise man knows himself to be a fool. William Shakespeare

25th October 2021, 07:01 AM	#128
RecoveringYuppy Penultimate Amazing Join Date: Nov 2006 Posts: 13,591	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.
	Last edited by RecoveringYuppy; 25th October 2021 at 07:02 AM.

25th October 2021, 07:11 AM	#129
Ziggurat Penultimate Amazing Join Date: Jun 2003 Posts: 51,989	Originally Posted by Puppycow 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.
	__________________ "As long as it is admitted that the law may be diverted from its true purpose -- that it may violate property instead of protecting it -- then everyone will want to participate in making the law, either to protect himself against plunder or to use it for plunder. Political questions will always be prejudicial, dominant, and all-absorbing. There will be fighting at the door of the Legislative Palace, and the struggle within will be no less furious." - Bastiat, The Law

25th October 2021, 08:16 AM	#130
Puppycow Penultimate Amazing Join Date: Jan 2003 Location: Yokohama, Japan Posts: 27,262	Originally Posted by RecoveringYuppy 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 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.
	__________________ A fool thinks himself to be wise, but a wise man knows himself to be a fool. William Shakespeare

25th October 2021, 08:30 AM	#131
theprestige Penultimate Amazing Join Date: Aug 2007 Location: The Antimemetics Division Posts: 60,326	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.
	__________________ There is no Antimemetics Division.

25th October 2021, 09:36 AM	#132
Ziggurat Penultimate Amazing Join Date: Jun 2003 Posts: 51,989	Originally Posted by theprestige 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.
	__________________ "As long as it is admitted that the law may be diverted from its true purpose -- that it may violate property instead of protecting it -- then everyone will want to participate in making the law, either to protect himself against plunder or to use it for plunder. Political questions will always be prejudicial, dominant, and all-absorbing. There will be fighting at the door of the Legislative Palace, and the struggle within will be no less furious." - Bastiat, The Law

25th October 2021, 11:05 AM	#133
Myriad The Clarity Is Devastating Join Date: Nov 2006 Location: Betwixt Posts: 19,248	I suspect the manned rescue mission would cost more than just building and launching another telescope.
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25th October 2021, 11:15 AM	#134
Trebuchet Penultimate Amazing Join Date: Nov 2003 Location: Port Townsend, Washington Posts: 34,461	But would it take as long? It began development in 1996 for a 2007 launch.
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25th October 2021, 03:20 PM	#135
Puppycow Penultimate Amazing Join Date: Jan 2003 Location: Yokohama, Japan Posts: 27,262	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.
	__________________ A fool thinks himself to be wise, but a wise man knows himself to be a fool. William Shakespeare

25th October 2021, 03:56 PM	#136
BowlOfRed Master Poster Join Date: Jul 2010 Location: Silicon Valley Posts: 2,172	I wonder if you could get odds from someone on the possibility that Hubble is still doing science when JWT is done.

25th October 2021, 05:59 PM	#137
Puppycow Penultimate Amazing Join Date: Jan 2003 Location: Yokohama, Japan Posts: 27,262	Originally Posted by BowlOfRed 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.
	__________________ A fool thinks himself to be wise, but a wise man knows himself to be a fool. William Shakespeare

25th October 2021, 06:37 PM	#138
theprestige Penultimate Amazing Join Date: Aug 2007 Location: The Antimemetics Division Posts: 60,326	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.
	__________________ There is no Antimemetics Division.

25th October 2021, 08:29 PM	#139
Blue Mountain Resident Skeptical Hobbit Join Date: Jul 2005 Location: Waging war on woo-woo in Winnipeg Posts: 7,032	Originally Posted by BowlOfRed 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)
	__________________ The social illusion reigns to-day upon all the heaped-up ruins of the past, and to it belongs the future. The masses have never thirsted after truth. They turn aside from evidence that is not to their taste, preferring to deify error, if error seduce them. Gustav Le Bon, The Crowd, 1895 (from the French)

25th October 2021, 11:19 PM	#140
BowlOfRed Master Poster Join Date: Jul 2010 Location: Silicon Valley Posts: 2,172	Originally Posted by Puppycow 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.

28th October 2021, 04:21 AM	#141
Steve001 Graduate Poster Join Date: Feb 2007 Posts: 1,788	Scheduled launch date December 18th 2021 An interesting read plus other interesting links. https://news.ucsc.edu/2021/10/jwst-launch.html
	Last edited by Steve001; 28th October 2021 at 04:23 AM.

28th October 2021, 05:27 AM	#142
Puppycow Penultimate Amazing Join Date: Jan 2003 Location: Yokohama, Japan Posts: 27,262	Originally Posted by BowlOfRed 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.
	__________________ A fool thinks himself to be wise, but a wise man knows himself to be a fool. William Shakespeare

29th October 2021, 09:43 AM	#143
steenkh Philosopher Join Date: Aug 2002 Location: Denmark Posts: 6,366	Isn’t 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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29th October 2021, 10:18 AM	#144
BowlOfRed Master Poster Join Date: Jul 2010 Location: Silicon Valley Posts: 2,172	Originally Posted by steenkh 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.

29th October 2021, 11:22 AM	#145
Blue Mountain Resident Skeptical Hobbit Join Date: Jul 2005 Location: Waging war on woo-woo in Winnipeg Posts: 7,032	Originally Posted by steenkh 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!
	__________________ The social illusion reigns to-day upon all the heaped-up ruins of the past, and to it belongs the future. The masses have never thirsted after truth. They turn aside from evidence that is not to their taste, preferring to deify error, if error seduce them. Gustav Le Bon, The Crowd, 1895 (from the French) Last edited by Blue Mountain; 29th October 2021 at 11:23 AM.

29th October 2021, 04:42 PM	#146
steenkh Philosopher Join Date: Aug 2002 Location: Denmark Posts: 6,366	Thanks, it sounds reassuring.
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29th October 2021, 04:50 PM	#147
theprestige Penultimate Amazing Join Date: Aug 2007 Location: The Antimemetics Division Posts: 60,326	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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29th October 2021, 10:02 PM	#148
Roboramma Penultimate Amazing Join Date: Feb 2005 Location: Shanghai Posts: 15,060	Originally Posted by theprestige 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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29th October 2021, 11:38 PM	#149
steenkh Philosopher Join Date: Aug 2002 Location: Denmark Posts: 6,366	Originally Posted by Roboramma "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 didn’t 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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30th October 2021, 04:39 AM	#150
Puppycow Penultimate Amazing Join Date: Jan 2003 Location: Yokohama, Japan Posts: 27,262	Originally Posted by steenkh 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.
	__________________ A fool thinks himself to be wise, but a wise man knows himself to be a fool. William Shakespeare Last edited by Puppycow; 30th October 2021 at 04:44 AM.

30th October 2021, 07:51 AM	#151
RecoveringYuppy Penultimate Amazing Join Date: Nov 2006 Posts: 13,591	Originally Posted by steenkh 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.

30th October 2021, 10:42 AM	#152
steenkh Philosopher Join Date: Aug 2002 Location: Denmark Posts: 6,366	Originally Posted by RecoveringYuppy 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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23rd November 2021, 09:32 AM	#153
wobs Master Poster Join Date: Oct 2011 Location: Hull Posts: 2,702	Delayed to the 22nd Dec: https://www.space.com/james-webb-spa...ay-december-22
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23rd November 2021, 10:47 AM	#154
Puppycow Penultimate Amazing Join Date: Jan 2003 Location: Yokohama, Japan Posts: 27,262	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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23rd November 2021, 11:21 PM	#155
Samson Penultimate Amazing Join Date: Oct 2013 Posts: 10,024	Originally Posted by Puppycow 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.