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#21
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The Hubble Space Telescope...
On Wed, 26 Nov 2003 20:08:04 -0000, "Brian Gaff"
wrote: I'd have thought that it might actually be useful to get it back and examine what and how it has aged in orbit. Not having much luck are they? They lost skylab, Mir was brought down, now although its possible, nobody wants to risk it for Hubble... Well, I expect they will pay for a dummy model to be made... There already is one... in Houston, I think. :-) Brian |
#22
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The Hubble Space Telescope...
Louis Scheffer wrote in
: This is not true, except for the very first batch of instruments, all long since replaced. There are no additional lenses in any of the insruments designed since the flaw was uncovered. In all the new instrucments, since they need one or more mirrors to direct the light within their own optics, they just need to make one or more of these mirrors not quite flat. This restores diffraction limited optical performance without adding any new elements. But since not flat is harder to make than flat. Is it still as good as it could have been if they did the job correctly the first time. You may think so. But I don't. Having worked at NASA and for Uncle some 26 years the one thing I learned is the PR is usually more optimisic than what reality is. David A. Scott -- My Crypto code http://cryptography.org/cgi-bin/cryp...c/scott19u.zip http://cryptography.org/cgi-bin/cryp...c/scott16u.zip http://www.jim.com/jamesd/Kong/scott19u.zip old version My Compression code http://bijective.dogma.net/ **TO EMAIL ME drop the roman "five" ** Disclaimer:I am in no way responsible for any of the statements made in the above text. For all I know I might be drugged. As a famous person once said "any cryptograhic system is only as strong as its weakest link" |
#23
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The Hubble Space Telescope...
In article ,
David A. Scott wrote: Interesting its not worth the RISK OF LIFE to bring it back but it is worth the RISK OF LIFE to attach a rocket to it to up burn it up in the atmosphere. No, the rocket attachment could be done as part of the last servicing mission (there is at least one more planned), so it would not involve any added risk. I wonder if anybody has done some sort of environmental study about the tradeoffs since the mission itself and the rocket attached will add more pollution to the air. Completely insignificant compared to all the other stuff that goes into the atmosphere. -- MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer pointing, 10 Sept; first science, early Oct; all well. | |
#24
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The Hubble Space Telescope...
(Explorer8939) wrote:
There may be a lot of magic involved in that operation. In many ways, the scenario is amazingly similar to the Skylab rescue plan, that would have used a teleoperated servicer to change the orbit of Skylab. We all know how that worked out. No, we don't know how it worked out. The plan was never carried out. D. -- The STS-107 Columbia Loss FAQ can be found at the following URLs: Text-Only Version: http://www.io.com/~o_m/columbia_loss_faq.html Enhanced HTML Version: http://www.io.com/~o_m/columbia_loss_faq_x.html Corrections, comments, and additions should be e-mailed to , as well as posted to sci.space.history and sci.space.shuttle for discussion. |
#25
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The Hubble Space Telescope...
In article ,
Explorer8939 wrote: There may be a lot of magic involved in that operation. In many ways, the scenario is amazingly similar to the Skylab rescue plan, that would have used a teleoperated servicer to change the orbit of Skylab. We all know how that worked out. Uh, yes; we know that the teleoperated servicer was never built and the scheduled reboost mission never flew. The reason for this isn't any intrinsic flaw with the concept - there are possible niggles, but there's plenty of time to work on them and we've got 25 years of orbital maintenance experience to do it with - but more the fact that Skylab turned out, er, not to be there any more. Not the best way to demonstrate that reboost missions are in some way known to be problematic, unless you're suggesting there's some kind of Solar Flux Karma going on... -- -Andrew Gray |
#27
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The Hubble Space Telescope...
Don't ask NASA if HST is better now than its pre-deploy specs, ask the
astronomers who've been able to write many wonderful papers based on their observations using the first generation instruments with COSTAR. David A. Scott wrote: Leaf Fan wrote in : Actually, if you'd like to look at the pre-launch specs and compare them to what COSTAR and the second generation instruments' corrective optics have provided, you'll find that HST is even better now than had the mirror been ground correctly the first time. This still makes be wonder how good would the so called second generation instruments be if the damn mirror was cut corectly the first time. I tend not to belive all the NASA hype since its in there interest to make things look better than they are. Its the nature of bad management which NASA seems to have no shortage of. David A. Scott |
#28
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The Hubble Space Telescope...
Ash Wyllie wrote: Leaf Fan opined Unfortunately many things changed after February 1. Even the official position of the astronaut office at JSC is that astronaut lives will not be risked for an HST retrieval mission, i.e. the benefit of returning HST to Earth is not worth the risko of astronaut lives. The risk is acceptable for servicing missions where the benefit is scientific knowledge. The HST Program did a study to determine what would have to be done to bring HST back to in the payload bay and while the study assumed Columbia, i.e. no external airlock, a return mission could be performed with an orbiter that has the external airlock, although additional work would have to be done (servicing hardware mods for HST to fit farther back in the bay). The current thinking is that some sort of propulsion module will be attached to HST to provide a controlled re-entry at the end of HST's life. If NASA is going to delibrately change Hubbles orbit, why not do 2 burns and boost into a 6,000km orbit and give some future generation the option of retrieving it for the Smithsonian? -ash for assistance dial MYCROFTXXX Boosting HST into a higher orbit has been discussed, but you'd have to ask those who said "no" why they don't want to leave HST retrieval to another generation. |
#29
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The Hubble Space Telescope...
Henry Spencer wrote: In article , David A. Scott wrote: Interesting its not worth the RISK OF LIFE to bring it back but it is worth the RISK OF LIFE to attach a rocket to it to up burn it up in the atmosphere. No, the rocket attachment could be done as part of the last servicing mission (there is at least one more planned), so it would not involve any added risk. More likely to be on SM-5 if the HST Program were lucky enough to get that. I wonder if anybody has done some sort of environmental study about the tradeoffs since the mission itself and the rocket attached will add more pollution to the air. Completely insignificant compared to all the other stuff that goes into the atmosphere. Current plan is to launch the prop module on an ELV when HST is no longer able to produce science. |
#30
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The Hubble Space Telescope...
"David A. Scott" wrote in message .1.4...
Louis Scheffer wrote in : [...] They just need to make one or more of these mirrors not quite flat. This restores diffraction limited optical performance without adding any new elements. But since not flat is harder to make than flat. Is it still as good as it could have been if they did the job correctly the first time. This is a reasonable question, but the answer is yes. The goal is to make all light paths equal length. If the primary mirror was perfect, then this mirror should be perfectly flat. With the mirror as is, it should be slightly (a few microns) curved. In either case, what determines the image quality is how far it deviates from the desired figure. You are right that it's harder to make, but since it's small and easy to measure in the lab, it's not too much harder, and the surface accuracy should be very similar. Efficiency losses due to surface accuracy are negligable after some point (lambda/14 is the cutoff usually used for radio telecopes, where these are called Ruze losses) and the mirror can be made much more accurately than that. The same technique is used, on purpose, in other telescopes where it removes much larger deviations. For example, Arecibo is a sphere, not a parabola. But with a few extra mirrors (which are not even remotely close to flat) they correct to diffraction limited performance. I believe optical telescopes designed for wide fields of view do similar tricks. So the short answer is, yes it's a little harder to make the mirror, but once it's done performance is identical to what it would be with a correct primary and a flat mirror. Lou Scheffer |
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