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

A Hubble Hubble wrote:


Current plan is to launch the prop module on an ELV when HST is no
longer able to produce science.

We should talk to the Russians; a modified Progress could do this job at
fairly low cost.

Pat

G EddieA95 wrote:

So, the Apollo 9 and 13 modules are definitely gone, the Apollo 10 module
is still of museum quality, and the rest of them would require a whole
bunch of restoration work to get them into a museum without a label
containing the word "debris" on it.

Nope, crashing into the moon at lunar orbital speed counts as "definitely
gone." Impact at 10,000 kph leads to dust, not salvage.

Which leaves A10 only, but we have no way of getting to it.

Your impact velocity seems a bit high, how about 6000 kph, which has about
a third the energy. Also, the initial impact would be at a very shallow
angle probably less than 5 degrees. One orbit it misses the lip of a crater
by a few inches, the next it hits it by a few inches. Shredding the lower
part of the orbiter, spinning the rest of it up into a huge shower of small
parts. Very small parts might survive such a shallow impact with soft moon
dust.

I wonder what size the largest parts would be, dust or maybe
some smaller parts survived, like the control handles that Neil Armstrong
was holding when he landed on the moon?

Craig Fink

Brian Thorn wrote:
On Sun, 30 Nov 2003 00:36:41 GMT, A Hubble Hubble
wrote:


Given that the FAWG is the only long range planning manifest that I know
of, and given that prior to the latest manifest only the first 4 flights
were not labelled "Under Review", but now all the flights up through
STS-124 (HST SM-4) are not "under review" and given that SM-4 was placed
where it is after discussions with the Administrator, I believe this
FAWG isn't going to change much (in terms of flight order) in the near
future.


You must not have been around in the post-Challenger return-to-flight
era. There were dozens of launch manifests over those 2 1/2 years, and
the flight order changed repeatedly. Just look at the STS order that
actually flew...

STS-26, 27, 29, 30, 28, 34, 33, 32, 36, 31... all those *before* the
big hydrogen leak fiasco hit in 1990.

Since those STS-numbers were approved by NASA officials at the very
top, this should serve as a warning not to give too much credence to
early return-to-flight launch schedules.

In other words, bank on the FAWG at your own peril.

Brian

Since this is an HST thread, I was specifically talking about SM-4's
relative placement in the manifest. The decision to fly it after core
complete and after 1E should keep SM-4 in the same relative position for
quite some time. As for the actual sequence of flights leading up to
core complete, I agree that those will probably change. However I don't
believe the FAWG will change much between now and when return to flight
is officially delayed (i.e. I personally don't believe return to flight
will happen in 2004).

On Sun, 30 Nov 2003 23:58:46 GMT, A Hubble Hubble
wrote:


STS-26, 27, 29, 30, 28, 34, 33, 32, 36, 31... all those *before* the
big hydrogen leak fiasco hit in 1990.

Since those STS-numbers were approved by NASA officials at the very
top, this should serve as a warning not to give too much credence to
early return-to-flight launch schedules.

In other words, bank on the FAWG at your own peril.

Brian

Since this is an HST thread, I was specifically talking about SM-4's
relative placement in the manifest.

Well, of the above numbers, 31 was the Hubble deploy mission. At one
time post-Challenger it was obviously considered the sixth mission
after Return-To-Flight. Look where it ended up.

I fully expect to see SM-4 scheduled for a time when all three
Orbiters are online, regardless of the Station assembly sequence.

Brian

Brian Thorn wrote:

On Sun, 30 Nov 2003 23:58:46 GMT, A Hubble Hubble
wrote:


STS-26, 27, 29, 30, 28, 34, 33, 32, 36, 31... all those *before* the
big hydrogen leak fiasco hit in 1990.

Since those STS-numbers were approved by NASA officials at the very
top, this should serve as a warning not to give too much credence to
early return-to-flight launch schedules.

In other words, bank on the FAWG at your own peril.

Brian

Since this is an HST thread, I was specifically talking about SM-4's
relative placement in the manifest.

Well, of the above numbers, 31 was the Hubble deploy mission. At one
time post-Challenger it was obviously considered the sixth mission
after Return-To-Flight. Look where it ended up.

I fully expect to see SM-4 scheduled for a time when all three
Orbiters are online, regardless of the Station assembly sequence.


From a practical standpoint all three Orbiters will most likely never be
online at the same time. The most that can practically be online at any one
time is two, the third will be missing some parts, canibalized to make the
other two flight worthy. So, to launch one, and have another ready and
operational on the pad will be a hard thing. Anytime NASA wants to fly the
canibalized Orbiter, they will have to have canibalize one of the two
operational Orbiters. So, for some time two Orbiter will be in a state of
canibalization. Additionally, after an Orbiter flys, it is down for some
time, that leaves only one operational Orbiter and the parts Orbiter during
this time.

Trying to keep a fleet of three complex vehicles all operational is
probably a logistical impossibility. Just keeping two operational at any
one time would be a logistical nightmare.

Also, from a safety standpoint, this will be a nightmare too. Unbolting and
rebolting pefectly good parts over and over again. Bending wires and
rebending wires over and over. Playing a shell game with perfectly good
parts going back and forth between Orbiters. Essentially, putting much more
wear and tear on good parts that should really be left alone. Each time
the part is moved, increasing the risk slightly, that something won't be
done right. Over torqued bolts, possibly stripping threads, under torqued
bolts, loose part, cracking wires, chafing wires, leaving debris where it
shouldn't be.

Craig Fink

Craig Fink wrote:
online at the same time. The most that can practically be online at any one
time is two, the third will be missing some parts, canibalized to make the
other two flight worthy.

This depends on just how much spare parts they had to begin with. They only
lost what was in Columbia. Any parts associated to Columbia that had not been
manifested for its last flight would become spares for other orbiters. (the
canadarm being an example).

If only 2 of 3 are the most that can be made available at one time, it is more
likely going to be because one has returned from a flight and is undergoing
post flight maintenance. With only 3 orbiters, one wonders if they will be
able to do major maintenance cycles on each orbiter and maintain adequate
launch rates.

Considering the amount of work needed to refurbish parts post-flight, I doubt
very much that NASA would be able to keep its launch schedule if one orbiter
had to wait for a just-landed orbiter to be taken araprt to extract the needed
part, then wait for that part to be refurbished and then installed into the
other orbiter.

And if some parts are reused more often than an orbiter itself, they will wear
out faster and need replacement. If they are able to replace parts that wear
out, they are able to bring their spares inventory to a level where they have
spares available for an orbiter.

Luba wrote:

Craig Fink wrote:
online at the same time. The most that can practically be online at any
one time is two, the third will be missing some parts, canibalized to
make the other two flight worthy.

This depends on just how much spare parts they had to begin with. They
only lost what was in Columbia. Any parts associated to Columbia that had
not been manifested for its last flight would become spares for other
orbiters. (the canadarm being an example).

If only 2 of 3 are the most that can be made available at one time, it is
more likely going to be because one has returned from a flight and is
undergoing post flight maintenance.

But if the Orbiter that just returned contains parts from one of the other
Orbiters, then only 1 Orbiter is flight worthy at that time.

With only 3 orbiters, one wonders if
they will be able to do major maintenance cycles on each orbiter and
maintain adequate launch rates.


Sure, the Orbiter being refurbished is available to be canibalized.


Considering the amount of work needed to refurbish parts post-flight, I
doubt very much that NASA would be able to keep its launch schedule if one
orbiter had to wait for a just-landed orbiter to be taken araprt to
extract the needed part, then wait for that part to be refurbished and
then installed into the other orbiter.

Yeah, that's why the minimum reasonable fleet size is three and not two.


And if some parts are reused more often than an orbiter itself, they will
wear out faster and need replacement. If they are able to replace parts
that wear out, they are able to bring their spares inventory to a level
where they have spares available for an orbiter.

I can imagine the lead time required to make a new spare can be quite large
for some things. If it takes two or three years to make a new spare, and
they are trying to fly all three Orbiters, your talking about switching out
the same part ten or twenty times instead of just once.

Looks like Endeavour is being canibalized as the first four flights are
Atlantis, Discovery, Atlantis and Discovery.

Craig Fink

On Mon, 1 Dec 2003, Craig Fink wrote:

Looks like Endeavour is being canibalized as the first four flights are
Atlantis, Discovery, Atlantis and Discovery.


Huh? The current manifest is taking into account for that fact that
Endeavour is in it's Orbiter Maintenace and Modification Period (OMMP).
If things stand as they are, the return to flight occurs in September
of 2004, then Endeavour will only just have returned from the OMMP, and be
just starting flight processing.
-Mike

Mike Dicenso wrote:



On Mon, 1 Dec 2003, Craig Fink wrote:

Looks like Endeavour is being canibalized as the first four flights are
KSC Web Site
Atlantis, Discovery, Atlantis and Discovery.
JSC Web Site
Atlantis,Discovery,US Orbiter,US Orbiter.

Huh? The current manifest is taking into account for that fact that
Endeavour is in it's Orbiter Maintenace and Modification Period (OMMP).
If things stand as they are, the return to flight occurs in September
of 2004, then Endeavour will only just have returned from the OMMP, and be
just starting flight processing.
-Mike