News: Hubble plans and policy

In article ,
Reed Snellenberger wrote:
This assumes that they don't remove all or part of the barrel/sunshade to
make it fit. Since the upper structure is a carbon-fiber lattice under a
cover, I imagine it would be pretty easy to cut through with the right
tool.

Unfortunately, the upper end is not *just* barrel, there's a lot of
equipment and other clutter attached. I doubt the practicality of cutting
a section off in orbit.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

On Sun, 28 Jul 2003, Jorge R. Frank wrote:

(Henry Spencer) wrote in
:

In article ,
rk wrote:
If they could service it, then it could be retrieved...

Not necessarily. This is why the loss of Columbia, in particular, is
a problem for a retrieval mission: Columbia was the only remaining
orbiter with an unobstructed cargo bay. Hubble is (if I'm not
mistaken) too big to fit in the cargo bay together with the external
airlock/docking-port assembly that the other orbiters now have in
there. They can fly a servicing mission, but would need extensive
reworking to fly a retrieval...

Right. Not a show-stopper but definitely a cost driver.

That can't be right. The Hubble is approximately 43 feet (13.1 meters)
long, which is about the same length as most of the ISS truss sections
launched so far. In fact, I believe that the PV6 truss and solar arrays
topped out around 49 feet, te absolute maximum length that anything can be
in orbiters equipped with an ODS assembly. So, no mods needed for any
orbiter going up on an HST retrieval mission.
-Mike

(Henry Spencer) wrote in
:

In article ,
Reed Snellenberger wrote:
This assumes that they don't remove all or part of the barrel/sunshade
to make it fit. Since the upper structure is a carbon-fiber lattice
under a cover, I imagine it would be pretty easy to cut through with
the right tool.

Unfortunately, the upper end is not *just* barrel, there's a lot of
equipment and other clutter attached. I doubt the practicality of
cutting a section off in orbit.

Henry:

I couldn't find a detailed (dimensioned) plan for the telescope, but the
diagram located at:

http://hubble.gsfc.nasa.gov/technology/parts.html

appears to show that the truss structure (including the secondary mirror
and the other 'clutter') ends approximately 7-9' from the end of
telescope itself. Assuming that the aperture door is designed with a
local motor connected to the telescope over a cable, it looks like there
isn't much there to get in the way.

You'd clearly need a NASA-spec pair of tinsnips (or equivalent), but
we've got several years to get that built. I assume that a 30' length
of primacord wouldn't be acceptable...

Just a thought.

--
Reed Snellenberger

In article ,
says...

snip

Well, at least the BBC online is very responsive to input from
readers. They currently are running a story on Watergate
conspirator Jeb Magruder claiming that Richard Nixon ordered
the Watergate break in, rather than just covering it up. In their
story, they said Nixon had been impeached. I e-mailed their
handy factual correction address to point out the error, and less
than an hour later they changed "Nixon was impeached and resigned"
to "Threatened by impeachment over the affair, Nixon resigned"

Articles of impeachment against Nixon were passed by the appropriate
House committee and sent to the floor of the House. Nixon resigned when
it became apparent that articles would be approved by the House and that
he didn't have enough votes in the Senate to win the trial. So, the
original BBC wording was indeed wrong and the corrected version, prompted
by your comment, was more correct. But it was more than just a threat --
it was pretty much guaranteed that Nixon would lose if he allowed the
process to continue. Otherwise, he wouldn't have resigned.

--

It's not the pace of life I mind; | Doug Van Dorn
it's the sudden stop at the end... |

On 28 Jul 2003 02:22:24 GMT, rk
wrote:

Henry Spencer wrote:

In article ,
rk wrote:
If they could service it, then it could be retrieved...

Not necessarily. This is why the loss of Columbia, in particular,
is a problem for a retrieval mission: Columbia was the only
remaining orbiter with an unobstructed cargo bay. Hubble is (if
I'm not mistaken) too big to fit in the cargo bay together with the
external airlock/docking-port assembly that the other orbiters now
have in there. They can fly a servicing mission, but would need
extensive reworking to fly a retrieval (and then after the
retrieval, you get to rework that orbiter again to put things back
the way they were).

Agreed. From memory, HST did take up the length of the bay.

Hubble measures 43.5 feet in length and 14 feet in diameter, so it
should fit within the 15 x 60 ft payload bay, even with the external
airlock. But it will be close.

Brian

On 28 Jul 2003 05:56:21 GMT, "Jorge R. Frank"
wrote:

Charles Buckley wrote in
:


Independent of the CAIB, NASA is studying the capability of ISS to serve as
a "safe haven" for a stranded shuttle crew. But with only four shuttle
flights per year, the ability of ISS to support a shuttle crew until the
next shuttle flight (even with three brought home in the Soyuz) is dubious.

If there is a serious problem with an Orbiter that prevents its safe
return, is NASA seriously going to consider launching a second
Orbiter? Look how long we're standing-down because of 107, 13 months
at the minimum, and it was pretty clear what felled Columbia within a
couple of weeks. Therefore, the idea of retrieving the Safe Haven crew
with another Shuttle would appear to be illogical. Unless NASA is
planning to fund increased Soyuz production, or magically acellerate
OSP production, the "Safe Haven" concept would seem to be a band-aid
applied to a severed artery. ISS can be a repair facility, perhaps. A
Safe Haven is not in the cards.

And why only four flights a year? The schedule was five per year
pre-107. With each Orbiter easily capable of three flights per year,
even a two-Orbiter fleet (with one in OMM) can support six flights per
year.

Brian

Henry Spencer wrote:
In article ,
Charles Buckley wrote:

...My understanding, which could be wrong, is that the weight limit is also
conditional about where the weight is applied. I am thinking that the
center of the bay has a lot less structural intergrity than the fore
or aft sections.


The issue is not structural strength, but flying behavior. The orbiter
has to function as an aircraft for descent and landing, and so the
position of its overall center of mass is quite important if stability and
control are to be satisfactory. Mary could doubtless explain the details
better than I could. :-)



She stated that the weight was within the CG limits, but I am not
sure if she was referring to the modified length of the payload bay
with the docking ring. Someone put the length on here and it was less
than the length of the bay with the adapter, but I could be mistaken.
This is not something they can just move around the bay. In it's
original launch, was HST fore, center, or aft in the bay? With the
adapter, the loading would be rather different than what the launch
config had.

A light payload can go almost anywhere, but a heavy one's center of mass
must be within a small volume (which does not include the geometric center
of the cargo bay -- something that really annoyed payload designers,
because tightly-packed payloads generally have their center of mass quite
close to their geometric center, and changing that is not easy).

In any case, Hubble fills essentially the entire cargo bay, and its own
center of mass has not changed much since launch, so that question is
pretty much moot. The problem is clearing the cargo bay -- not an easy
task for the remaining orbiters, which have had the airlock moved out of
the cabin. (The presence of an airlock is non-negotiable, even on a
flight with no scheduled spacewalks, because it is required for certain
emergency procedures.)

So, even with the adapter taken off, then had the HST been launched
foreward in the bay, there is a good chance this would push it aft. Hmm.
Winging this.. Given the design contraint that the CG was not located
near the center of the Bay, they would likely have designed HST with
an off-center mass that was far enough towards one end of the HST that
it could be mounted center and still have it's CG outside the limits of
the bay. Now, if the original launch config had been aft with the CG
on the foreward side, then this would not be affected much by adding an
airlock into the bay. But, if it was mounted in the middle with a
foreward CG, then shifting it aft could put it's CG into the center of
the bay.

This mission is impossible without an airlock, so that really does put
in that constraint.

Mary Shafer wrote:
On 27 Jul 2003 23:59:31 GMT, "Jorge R. Frank"
wrote:


Mary Shafer wrote in
m:


On Sun, 27 Jul 2003 05:11:47 -0600, Charles Buckley
wrote:


Recovery? That would mean loading a big heavy Hubble into the
payload bay of a shuttle and returning it to Earth, correct?

I suspect that Hubble would be pushing the return capability of
the Shuttle.

Er, Hubble was launched in the Orbiter and the Orbiter never carries
anything it can't land with safely. Otherwise the abort modes would
be impossible.

That was my answer, too... I've since learned that only the "nominal"
landing weight/CG limits are certified for multiple landings; the "abort"
limits are certified for one time only. That doesn't mean the airframe is a
write-off after an abort landing, but it does mean NASA would want to go
over it a little more thoroughly than normal.


This is my understanding, too. Of course, this is pretty much
standard procedure for any vehicle. The main reason for this for the
Orbiter is there's no good way to dump the OMS fuel in an abort,
unlike most aircraft, so they have to land at a heavier weight
aborting than they would in a regular landing.

Normally, an airplane will fly around and burn off or dump enough fuel
to get it down well within the landing weight limits, mostly so it
will stop before the end of the runway without setting the tires,
wheels, and brakes, or even the entire aircraft, on fire. Yes,
aircraft are certified to land at GTOW on a normal-length runway
without any flames, but those tests assume a highly-trained test pilot
with plenty of practice, optimal energy management, and a clean, dry
runway. Still, I'd rather do an immediate 180 in an airliner and land
heavy than do an RTLS or a TAL. An AOA doesn't seem as dicey, though.


Hubble definitely falls under the nominal landing weight limit; it's only
24,500 lb, well under half the shuttle's lift capacity. I'm not sure about
the CG limit, but as you say, it has to be within the abort limit or they
wouldn't have launched it in the first place.


I'm sure about the CG limits because my husband was on the group that
set the CG envelope. Hubble is well within the envelope. I just
asked him. Some references are easy to find, rather than being packed
away in a carton somewhere.

Mary



Henry keeps mentioning modifications to be the Bay since that time.
One of the things he mentions is the adapter. The other an external
airlock. Would either of these shift the mounting point of the HST from
it's launch config? Also, is the CG limits applicable across the whole
vehicle, or limitted to specific sections of the bay? If the HST can not
be mounted in it's original config, then this is a whole new set of
variables to be weighed. It could easily have been shifted outside the
CG envelope should there have been the wrong types of mods since the
original launch.

From what I am seeing, they can not just take the original numbers
because the variable is not the Hubble, but the launch vehicle.

On Mon, 28 Jul 2003 21:01:57 -0600, Charles Buckley
wrote:

Henry Spencer wrote:
In article ,
Charles Buckley wrote:

...My understanding, which could be wrong, is that the weight limit is also
conditional about where the weight is applied. I am thinking that the
center of the bay has a lot less structural intergrity than the fore
or aft sections.


The issue is not structural strength, but flying behavior. The orbiter
has to function as an aircraft for descent and landing, and so the
position of its overall center of mass is quite important if stability and
control are to be satisfactory. Mary could doubtless explain the details
better than I could. :-)

She stated that the weight was within the CG limits, but I am not
sure if she was referring to the modified length of the payload bay
with the docking ring.

I said the CG was within the CG limits and the weight was within the
weight limits.

The way you do the CG is to take the mass and CG position of the added
item (Hubble, in this case) and multiply the mass times the moment arm
between the vehicle CG and the item CG and add it to the vehicle CG to
get the new CG. If that CG is within limits, everything's fine.

If you can get Hubble into the payload bay, the new CG will be within
the limits.

Someone put the length on here and it was less
than the length of the bay with the adapter, but I could be mistaken.
This is not something they can just move around the bay. In it's
original launch, was HST fore, center, or aft in the bay?

Yes.

A light payload can go almost anywhere, but a heavy one's center of mass
must be within a small volume (which does not include the geometric center
of the cargo bay -- something that really annoyed payload designers,
because tightly-packed payloads generally have their center of mass quite
close to their geometric center, and changing that is not easy).

In any case, Hubble fills essentially the entire cargo bay, and its own
center of mass has not changed much since launch, so that question is
pretty much moot. The problem is clearing the cargo bay -- not an easy
task for the remaining orbiters, which have had the airlock moved out of
the cabin. (The presence of an airlock is non-negotiable, even on a
flight with no scheduled spacewalks, because it is required for certain
emergency procedures.)

So, even with the adapter taken off, then had the HST been launched
foreward in the bay, there is a good chance this would push it aft. Hmm.

Nope. Adding something with a forward CG moves the CG forward. How
much depends on how heavy the item is and where its CG is.

Winging this.. Given the design contraint that the CG was not located
near the center of the Bay, they would likely have designed HST with
an off-center mass that was far enough towards one end of the HST that
it could be mounted center and still have it's CG outside the limits of
the bay.

No, they couldn't. The CG is well within the payload bay. In fact,
it's on the centerline laterally, it's at about the mid waterline, and
it's somewhere around 30% MAC (although that's arbitrary because of
the way they define MAC, but that's never bothered anyone).

No matter what you put in the payload bay, if its CG is anywhere near
its geometrical center and it mostly fills the bay, the CG won't move
that much.

By the way, the Orbiter CG is, roughly, in the middle of the Orbiter.
It's just that the payload bay isn't. We don't care about the CG of
the payload pay or the payload, except in how the payload CG and mass
affect the Orbiter CG.

The Orbiter CG envelope is pretty robust. It's not a limited to a few
inches longitudinally. It's more like a few feet. Ditto laterally
and vertically. The Orbiter is a big vehicle with big control
surfaces and a big body flap to trim with.

Now, if the original launch config had been aft with the CG
on the foreward side, then this would not be affected much by adding an
airlock into the bay. But, if it was mounted in the middle with a
foreward CG, then shifting it aft could put it's CG into the center of
the bay.

You don't get it. We don't care about Hubble's CG. It's not
important. It's just riding along in the Orbiter.

We care only about the Orbiter's CG. It's very important. Why?
Dynamic stability, static stability, control authority, trim
capability. This all matters when it's flying aerodynamically, not
ballistically. Which is to say, when it's re-entering and landing.

The Orbiter isn't flying aerodynamically during launch.

So all we care about Hubble's CG is that it not move the Orbiter CG
out of the envelope. But we know it won't because we launched it with
the Orbiter, meaning it didn't move it too much.

This mission is impossible without an airlock, so that really does put
in that constraint.

--
Mary Shafer Retired aerospace research engineer

"A MiG at your six is better than no MiG at all."
Anonymous US fighter pilot

"Dale" wrote:
On Sun, 27 Jul 2003 06:44:57 -0500, "Paul F. Dietz" wrote:

The real justification for retrieval is to avoid dropping debris
on anyone when it reenters. This saves a certain number of lives
on average. If this number is less than the expected number of
lives lost in a shuttle mission, the recovery is not worth doing.

You mean "possible" number, not "expected" number, right?
I'd like to think they always launch with an expected number
of lives lost of "zero".

Expected value, as in statistics. Probability times magnitude,
more or less. So, say the probability of the Shuttle coming
apart on reentry is 1%, the number of deaths would likely be
about 7, so the expected number of crew deaths per reentry would
be .07. The calculation on the other side is more difficult to
fudge into an easy mold because of the wide variation in possible
number of deaths on the ground in the event of a ground strike
(ranging from zero to a busload, perhaps), but I think you get
the general idea.