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#180
by
Jim
on 09 Dec, 2014 15:04
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In your opinion perhaps - but servicing our brand new $8 Billion telescope may someday become a necessity and a true test.
Not an opinion. Both are truly bad ideas, wastes of money. JWST is not designed for servicing.
That would be throwing good money at bad.
Aside from HST and ISS, science missions (like Cassini) are not designed for repair.
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#181
by
llanitedave
on 09 Dec, 2014 15:35
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Hubble is done when it fails, the replacement is the JWST.
Actually, it isn't, due to different wavelengths.
Once HST batteries and gyros start to fail, you will hear more about this as the scientists demand that Hubble be serviced.
More likely the demand will be for a new and larger instrument.
knew this was coming.....NASA has those two old spy sats they could rework and launch. A lot cheaper than another Hubble servicing. However in light of JWST costs its going to be a hard sell.
JWST costs had very little to do with the optics, and very much to do with the need to maintain and extremely stiff and lightweight structure at very low temperatures to reduce IR interference. An instrument designed for optical wavelengths would not have nearly such onerous requirements. I'd guess an 8m spin-cast monolithic mirror with a nice high-resolution instrument package could be built and launched on SLS for not much cost difference than an Orion service mission to Hubble.
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#182
by
Danderman
on 09 Dec, 2014 15:40
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There is a separate thread for JWST servicing. Please keep this thread to the wonderful idea of servicing Hubble using Orion.
The question is which launcher would be suitable for Orion to attain the 600 km HST orbit?
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#183
by
Jim
on 09 Dec, 2014 16:13
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I'd guess an 8m spin-cast monolithic mirror
where would such a mirror be built and how would it get to the spacecraft manufacture and then to the launch site?
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#184
by
Jim
on 09 Dec, 2014 16:18
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There is a separate thread for JWST servicing. Please keep this thread to the wonderful idea of servicing Hubble using Orion.
Why? Neither are wonderful. Why not keep the farcical topics to a limited part of the forum so as not to infect the rest of it.
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#185
by
bob the martian
on 09 Dec, 2014 18:35
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The question is whether a HST batteries and gyros service/replacement mission can be done in principle, ignoring any issues of politics or cost or sensibility, using the Orion spacecraft as it will most likely be configured for a real manned flight. This means:
1. No arms, booms, or other sticky-outy bits
2. No special purpose mission modules
3. HST batteries and gyros will be carried in the Orion spacecraft, along with EMUs and all the necessary tools
Not being an engineer, rocket scientist, or other expert, the issues that come to mind are as follows:
1. Volume constraints - the batteries and gyros by themselves may fit within the Orion spacecraft volume. However, the spacecraft volume must also contain racks or palettes to secure the batteries and gyros, along with EMUs, tools, and, oh yeah, the meat sacks;
2. Aperture constraints - it doesn't matter if the interior volume of Orion can accomodate the batteries and gyros if they don't fit through the hatch (and that picture of the fully assembled battery pack has me dubious); I haven't found the dimensions for it after some cursory googling, so I don't know whether they will or not;
3. Translating/positioning the parts - This, to me, kills the whole mission dead - once at the HST, the astronauts have to get the batteries and gyros out of the Orion spacecraft and over to the HST, meaning at least two people in bulky EMUs are going to get to manhandle 400 lbm units off their palettes/racks, maneuver them within the spacecraft and through a hatch without banging them against, say, a control panel or something, then somehow translate themselves and the parts and their tools from the spacecraft to HST without a powered boom or an arm, which means going hand-over-hand along a rail or tether, which means they need both hands free, which is going to make it somewhat difficult to hold on to the spare parts, then they get to position said parts into the right place on the HST, using nothing but their own muscle power the whole time.
You'd want at least 3 astronauts for such a mission for safety's sake (have at least one crew member who isn't exhausted from humping 400 lbm batteries from one spacecraft to another), ideally 4 so you can have two shifts, because you know it's going to take multiple trips, which implies multiple depress/repress cycles. You'd also want a way to secure the two spacecraft together; you wouldn't want them to be in free drift relative to each other.
So, no. Not without a specialized service module, not without an arm.
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#186
by
llanitedave
on 09 Dec, 2014 23:35
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I'd guess an 8m spin-cast monolithic mirror
where would such a mirror be built and how would it get to the spacecraft manufacture and then to the launch site?
How do 8m mirrors get to the observatory sites? The aren't cast on site. But they get there.
Steward Observatory has a facility located underneath the University of Arizona football stadium that spin-casts honeycomb telescope mirrors up to 8.4 meters in diameter. Those mirrors are already used in several observatories, including The large Binocular Telescope on Mt. Graham, which has a pair of 8.4m mirrors, the Large Synoptic Survey Telescope, now under construction in Chile, and 3 of the 7 mirrors of the Giant Magellan Telescope, with 4 more still to be cast.
They haven't given up just because the mirrors are too large for a regular truck bed.
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#187
by
newpylong
on 10 Dec, 2014 14:12
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In your opinion perhaps - but servicing our brand new $8 Billion telescope may someday become a necessity and a true test.
Not an opinion. Both are truly bad ideas, wastes of money. JWST is not designed for servicing.
That would be throwing good money at bad.
Aside from HST and ISS, science missions (like Cassini) are not designed for repair.
Then why is there a docking ring on it? It's not designed for servicing but there are contingencies.
So, opinion. Your opinion != fact
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#188
by
Jim
on 10 Dec, 2014 14:33
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Then why is there a docking ring on it?
Are you sure it is still on the spacecraft?
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#189
by
newpylong
on 10 Dec, 2014 15:03
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Then why is there a docking ring on it?
Are you sure it is still on the spacecraft?
I haven't seen anything that that particular feature has been removed in the design. Have you?
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#190
by
arachnitect
on 10 Dec, 2014 19:47
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Then why is there a docking ring on it?
Are you sure it is still on the spacecraft?
I haven't seen anything that that particular feature has been removed in the design. Have you?
I don't see much evidence that this feature actually made it into the final design, either. I can't find any recent references to any kind of docking or grapple fixture.
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#191
by
woods170
on 11 Dec, 2014 11:09
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Then why is there a docking ring on it?
Are you sure it is still on the spacecraft?
I haven't seen anything that that particular feature has been removed in the design. Have you?
Then why is there a docking ring on it?
Are you sure it is still on the spacecraft?
I haven't seen anything that that particular feature has been removed in the design. Have you?
I don't see much evidence that this feature actually made it into the final design, either. I can't find any recent references to any kind of docking or grapple fixture.
And that is quite correct. The very reason why Jim hinted at it.
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#192
by
newpylong
on 11 Dec, 2014 11:20
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If something is known come right out and say it. We don't get gold stars for guessing hints.
That's an interesting change nonetheless. What is the evidence for the omission?
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#193
by
arachnitect
on 11 Dec, 2014 16:16
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If something is known come right out and say it. We don't get gold stars for guessing hints.
That's an interesting change nonetheless. What is the evidence for the omission?
I just can't find any references to such a thing from the last 5 or 6 years (since the 2011 re-baseline). There are no pictures or mentions of it being assembled. It's not on the latest renderings. The JWST website doesn't say anything about a docking/grapple fixture, but does say that JWST can't be serviced.
There's only one place to put a docking fixture like LIDS/NDSS (whatever it's called nowadays) and it just isn't there. It's possible they've hidden an FRGF or other grapple fixture somewhere, but I can't find any reference to that either.
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#194
by
pagheca
on 11 Dec, 2014 16:51
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If something is known come right out and say it. We don't get gold stars for guessing hints.
That's an interesting change nonetheless. What is the evidence for the omission?
Servicing a serviceable system in low orbit like HST is complicated. Servicing something that is not designed to be serviceable in L2, like the JWST, is impossible. As simple like that.
You cannot bend the reality of things, and there are
plenty of official resources about the JWST online clearly saying it is not serviceable.
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#195
by
jgoldader
on 11 Dec, 2014 17:30
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All the HST servicing support stood down after the last servicing mission. People reassigned, hardware disposed of, etc.
The large ground-based telescopes with adaptive optics will be routinely giving better imaging than Hubble, or are doing that already. The main loss is the high resolution UV that only a space telescope can give. There was a proposal by Johns Hopkins to fly a UV telescope with the UV instruments that went up on the last servicing mission, back when that flight didn't look likely to happen. (IIRC, the proposal was called HOP, the Hubble Origins Probe.) A 1.5-m UV-optimized with an imager and spectrometer could recover most of the unique science that will be lost when HST finally goes.
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#196
by
Bob Shaw
on 13 Dec, 2014 00:25
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JWST has a grapple fixture. It was forced onto the spacecraft at the last minute, but will be there. It's for, er, *grappling*. Which implies...
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#197
by
jgoldader
on 14 Dec, 2014 12:52
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JWST has a grapple fixture. It was forced onto the spacecraft at the last minute, but will be there. It's for, er, *grappling*. Which implies...
HST was designed to be serviced. JWST was designed to not be serviced. The word order matters here. There are no handholds, and no foot restraints for astronauts to use. There are no bays meant to be opened by astronauts. The mirror is out in the open, and my ex-astronomer gut tells me that contamination from RCS products would be Very Bad for the optics.
If there's a grapple fixture on JWST, the only possible reason is to guard against complete LOM due to a deployment failure. If JWST doesn't work because it couldn't deploy itself properly, the hearings will make the HST spherical aberration look like a kindergarten party.
But its existence doesn't mean the grapple would be useful. It would be years before a rescue mission could be mounted (you'd need a non-existant hab module for starters), and some failures (the sunshade getting tangled, say) might be beyond repair. And again, my guess is the optics would be contaminated enough by Orion's RCS that the telescope's science goals would be compromised. I know the folks at STScI are capable of near-miracles, so I bet they could recover some science, but it would be really compromised (example: deconvolution of the aberrated HST images recovered some science before the servicing missions installed corrections for the optics; but we later saw many cases, like Eta Carinae, where what we believed we were seeing in deconvolved images was shown to be just plain wrong once we had the corrective optics installed).
I've seen enough weird deployment failures to think putting 1-2 small RMS analogues on especially valuable satellites with deployable parts might be a good idea. Give the arms enough strength to give a good push or pull and a small camera for inspection. AFAIK, JWST has no selfie-cams, so if something fails in the deployment sequence, we might not be able to tell why. I suspect there's enough instrumentation to give a detailed understanding of the configuration, but not necessarily why the telescope is in that configuration.
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#198
by
Hog
on 15 Dec, 2014 00:05
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All the HST servicing support stood down after the last servicing mission. People reassigned, hardware disposed of, etc.
The large ground-based telescopes with adaptive optics will be routinely giving better imaging than Hubble, or are doing that already. The main loss is the high resolution UV that only a space telescope can give. There was a proposal by Johns Hopkins to fly a UV telescope with the UV instruments that went up on the last servicing mission, back when that flight didn't look likely to happen. (IIRC, the proposal was called HOP, the Hubble Origins Probe.) A 1.5-m UV-optimized with an imager and spectrometer could recover most of the unique science that will be lost when HST finally goes.
Depends what your goal is "better" is subjective in this case.
Even before Hubble was launched, there were techniques that allowed for better resolution from ground bases telescopes, though back in the 90's HST could look at MUCH dimmer objects(edit: 8 magnitudes dimmer than 90's ground based using aperture masking inferiometry).
Its not all about resolution.
"The usefulness of adaptive optics versus HST observations depends strongly on the particular details of the research questions being asked. In the visible bands, adaptive optics can only correct a relatively small field of view, whereas HST can conduct high-resolution optical imaging over a wide field. Only a small fraction of astronomical objects are accessible to high-resolution ground-based imaging; in contrast Hubble can perform high-resolution observations of any part of the night sky, and on objects that are extremely faint."
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#199
by
jgoldader
on 15 Dec, 2014 10:19
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Depends what your goal is "better" is subjective in this case.
Even before Hubble was launched, there were techniques that allowed for better resolution from ground bases telescopes, though back in the 90's HST could look at MUCH dimmer objects(edit: 8 magnitudes dimmer than 90's ground based using aperture masking inferiometry).
Its not all about resolution.
"The usefulness of adaptive optics versus HST observations depends strongly on the particular details of the research questions being asked. In the visible bands, adaptive optics can only correct a relatively small field of view, whereas HST can conduct high-resolution optical imaging over a wide field. Only a small fraction of astronomical objects are accessible to high-resolution ground-based imaging; in contrast Hubble can perform high-resolution observations of any part of the night sky, and on objects that are extremely faint."
Creating artificial guide stars using lasers and multi-conjugate AO (adaptive optics) have gone far to mitigate the need for natural AO guide stars and small isoplanatic patch size. Of course, we can't do much about the night sky brightness, you're right. But there is JWST coming up, and if it works as intended, it will see far deeper than HST.
But JWST is an IR telescope, with no UV and little if any optical instrumentation (there was a plan to go down to about 650nm, but wasn't it either eliminated or the requirements loosened years ago? I forget). There's lots of interesting science that can be done between 91 nm (or 122 for Lyman alpha) and ~400 nm. The atmosphere blocks light at those wavelengths, but it's where hot stars have most of their really important diagnostic spectral features. When HST is gone, we won't have much in orbit to do science there, spectroscopy in particular. I remember a bitter quote from many years ago, lamenting that it would be a shame if we had a Milky Way supernova go off and couldn't observe it in the UV.
Don't get me wrong, I'm as big a fan of space telescopes as you'll find--I used HST!--but at some point we have to let HST go and move on. I will have a good cry when that happens. I will especially lament the loss of the UV, though. I wish we had a plan of regularly (5-7 yrs cadence) launching meter-class or so observatories. It would be great for spurring instrument and tech development, and there would be many eggs in many baskets. You could have them focus on particular science areas, with a clear target of opportunity program that's more open. But alas.