The Hubble Space Telescope...

A Hubble Hubble wrote in
:

Jorge R. Frank wrote:
(Explorer8939) wrote in
m:

Johnson Space Center wants to use 2 Shuttles for a
servicing mission, one for the prime mission, one as a backup in case
the first Shuttle has problems inflight and the crew needs to be
rescued.

Incorrect. JSC is *studying* the option of a rescue shuttle in the
even that GSFC *wants* an HST servicing mission before the shuttle
program has standalone repair capability. JSC does not *want* to use
a rescue shuttle; it would *prefer* to delay the next HST servicing
mission until standalone repair capability is available.

It is my understanding that the HST mission will not fly until there
is a tile repair procedure in place that does not require the orbiter
to be attached to the station. RCC repair is another matter. There
may never be an RCC repair procedure for holes greater than a certain
size, so if that were to happen again,

Keep in mind that once the ET foam-shedding problem is mitigated, this is a
*very* low-probability event.

station would be the safe haven
for the crew during an ISS mission. Since there is no "safe heaven"
in the HST orbit plane, the NASA powers that be have decided to have
that stand-by shuttle on the pad for a crew rescue.

Almost true, except for your use of "have decided". That is incorrect. The
correct words would be "are studying".


--
JRF

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In message , Scott M. Kozel
writes

If a future space telescope gets placed at one of the Earth's stable
Lagrange points, as has been proposed, it is highly unlikely that any
mission will ever be sent to bring it back to earth. The L4 and L5
points are 93 million miles from Earth. Manned service missions
probably would be infeastible, also, at such a distance.

What would be the advantage of doing that, as opposed to putting it at
the L1 or L2 points, or simply letting it drift away from Earth, all of
which have been done? You're just adding complexity in terms of
manoeuvring, and anyway the L4 and L5 points aren't that stable. There
are not many natural objects (are there any?) there, for instance.
I'd love to see the L3 point, though.
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In message , Jorge R. Frank
writes
"Scott M. Kozel" wrote in
:

Some of the proposals for an L4 or L5 space telescope, have suggested
that it would be cheaper to send it there on one-shot basis, that when
it wears out it won't be serviced, but that a new space telescope will
be sent to take over the work.

I agree. Indeed, the same argument could have been made for LEO in the
70's.

It was made.
"According to Riccardo Giacconi (who went on ... to become the first
director of the Space Telescope Science Institute :-) [my smiley]
_seven_ similar space telescopes could have been built and launched with
separate expendable rockets for what has so far been spent on just one.
Even then, each space telescope would still have cost several times more
than the largest ground-based telescope".
From "Before the Beginning" by Michael Rees.
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In message
, A Hubble
Hubble writes


Craig Fink wrote:

I would prefer they use that propulsion module to boost it into a much
higher orbit where it could stay until we have a new generation of space
plane to bring it back.

I agree with you 100%, it wouldn't take much to give the Hubble a
50 year or more orbital lifetime. Put it in a stable gravity gradiant
attitude and let someone in the future pick it up and bring it down.
Close the sunshield cover, and the inside of the sunshield tube would
still be a good millenium orbital debris (control set) data point for future.
Craig Fink

I agree with that sentiment, but when you consider what would be
involved in designing a retrieval mission far down the road, it would
be a rather ambitious attempt. What would the condition of HST be
after prolonged exposure to the space environment? What kind of return
vehicle would have to be designed to retrieve HST, not just to hold it
but also to ensure it survives landing loads? I'd love to see HST in a
museum after its useful life has ended, but pragmatically, I don't see
how it can happen (in my lifetime).

I don't know how old Craig is :-) but isn't that exactly what he is
saying? Move it into high orbit, where it will provide useful data on
space conditions (and be less prone to damage by reactive oxygen, as
happens in LEO) and leave the problem of fetching it to our
grandchildren.
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In message , Scott M. Kozel
writes

That is basically what I thought. I think that it would be fascinating
to some day be able to see the HST in the Smithsonian Air and Space
Museum, and that would be easy for me as the new museum annex is less
than 100 miles from where I live (Virginia); but I can't see the
justification for a $500+ million shuttle mission being built around
a returning the HST if the mission is not justifiable for non-HST
reasons.

Surely you can see the HST (or its spare), unless it's been removed?
They even took a component from it for a servicing mission. Let it go.
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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

"Scott M. Kozel" wrote in
:

The L2 point is a lot closer, but it might take a lot more fuel to
keep such a spacecraft properly positioned, which would either require
manned servicing missions, or would shorten the life of a one-shot
spacecraft.

The other side of the tradeoff is that L4/L5, being almost 50 times
farther, will require the telescope to have a much larger antenna, a much
more powerful transmitter, and more electrical power to drive the
transmitter. If a large high-gain antenna is required to get adequate
bandwidth, and large solar arrays are required to get adequate power, it
sets up an unpleasant tradeoff between telescope pointing, solar array
pointing, and antenna pointing. You can possibly remove the solar array
pointing constraint by using an RTG.

--
JRF

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In message , Jorge R. Frank
writes
"Scott M. Kozel" wrote in
:

The L2 point is a lot closer, but it might take a lot more fuel to
keep such a spacecraft properly positioned, which would either require
manned servicing missions, or would shorten the life of a one-shot
spacecraft.

The other side of the tradeoff is that L4/L5, being almost 50 times
farther, will require the telescope to have a much larger antenna, a much
more powerful transmitter, and more electrical power to drive the
transmitter. If a large high-gain antenna is required to get adequate
bandwidth, and large solar arrays are required to get adequate power, it
sets up an unpleasant tradeoff between telescope pointing, solar array
pointing, and antenna pointing. You can possibly remove the solar array
pointing constraint by using an RTG.


Deep space probes have always been dominated by their antenna, but
what's the current status of laser communications? In either case, are
you really worried about just where the telescope is, unless you plan
doing interferometry or looking for asteroids? The important thing is
pointing accuracy and that's easier away from Earth - no thermal stress
from being in orbit, no forbidden areas because the Earth is in the way.
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In message , Jorge R. Frank
writes
"Scott M. Kozel" wrote in
:

The L2 point is a lot closer, but it might take a lot more fuel to
keep such a spacecraft properly positioned, which would either require
manned servicing missions, or would shorten the life of a one-shot
spacecraft.

The other side of the tradeoff is that L4/L5, being almost 50 times
farther, will require the telescope to have a much larger antenna, a much
more powerful transmitter, and more electrical power to drive the
transmitter. If a large high-gain antenna is required to get adequate
bandwidth, and large solar arrays are required to get adequate power, it
sets up an unpleasant tradeoff between telescope pointing, solar array
pointing, and antenna pointing. You can possibly remove the solar array
pointing constraint by using an RTG.


Deep space probes have always been dominated by their antenna, but
what's the current status of laser communications? In either case, are
you really worried about just where the telescope is, unless you plan
doing interferometry or looking for asteroids? The important thing is
pointing accuracy and that's easier away from Earth - no thermal stress
from being in orbit, no forbidden areas because the Earth is in the way.
--
Rabbit arithmetic - 1 plus 1 equals 10
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Once in a HEO, the HST will never spiral in. Its orbit will gradually open
up until ultimately it escapes from Earth gravity altogether.

Its the same physics which causes the Moon to drift away about two inches
per year. Anything out of atmospheric drag drifts away.

Therefore, future generations won't have to deal with the HST if they don't
want to; they can just forget about it because it will go away on its own.