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The Hubble Space Telescope...



 
 
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  #21  
Old November 27th 03, 09:14 PM
Brian Thorn
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Default 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  
Old November 29th 03, 01:27 AM
David A. Scott
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Default 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
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  #23  
Old November 29th 03, 04:05 AM
Henry Spencer
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Default 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.
--
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pointing, 10 Sept; first science, early Oct; all well. |
  #25  
Old November 29th 03, 01:13 PM
Andrew Gray
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Default 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  
Old November 30th 03, 01:14 AM
A Hubble Hubble
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Default 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  
Old November 30th 03, 01:22 AM
A Hubble Hubble
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Default 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  
Old November 30th 03, 01:27 AM
A Hubble Hubble
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Default 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  
Old November 30th 03, 07:24 AM
Lou Scheffer
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Default 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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