MSNBC (JimO) - Hubble debate -- a lot of sound and fury

On Fri, 2 Apr 2004 11:51:51 +0100, "John"
wrote:

It's as much of a problem as you make it. If you can park the hubble within
a few hundred meters from the ISS you can effectively attach a line and real
it in.

How do you stop the 24,000 lb. Hubble once you've begun reeling it in?
It has no brakes, and will crash into ISS unless you catch it just
right with the SSRMS (if you miss, you get another
Progress/Spektr-class event... not good.)

Brian

"Jorge R. Frank" wrote:
That is not to say that it's impossible to develop an automated system to
rendezvous and capture a non-cooperative, inert, and (by 2007-08) possibly
slowly tumbling target. But the challenge of developing such a system will,
IMO, be greater than that of getting the ion propulsion to work.

With the growing problem of space debris and the need to deorbit
'dead' brid, the development of such a system might not be entirely a
bad idea. (Or at least a serious study to develop a theory.)

D.
--
Touch-twice life. Eat. Drink. Laugh.

"Jorge R. Frank" wrote ...

It is. How do you plan to attach the line, for one? An EVA crewmember
can't
go out that far from ISS; SAFER doesn't carry enough gas and is
zero-fault-
tolerant. It's really just an emergency rescue device, not like the MMU.

Yeah well, that's just an arguement against the use of manned space
stations. If they can't do something as relatively simple as this without
turning it into a horrendously complicated affair...

All you'd need is a glorified pogo stick and a safety cord. You hit hubble
or you don't. If you don't you reel yourself back in and try again. This is
of course a heath robinson approach, and I'm willing to believe there woudl
be technical and safety issues. But I really would like to know why NASA
never uses the space-pencil approach more often.

The serious answer is if it's only a few hundred meters away the space
shuttle can safely grab it without fear of not being able to get to he ISS.

The OTV won't keep going perfectly forward due to orbital mechanics, which
causes some decidedly non-intuitive effects in LEO. The OTV must have the
capability to constantly correct its lateral alignment as it approaches.

I've assumed the hubble is still active and able to control it's direction.
If so, would it make more sense to have the hubble line up to the OTV,
rather than the other way round? The hubble is a supurbly accurate pointing
device after all. See below crude graphic. Even though the OTV is off
target, it's both enough that they can compensate by making sure they are
constantly pointing towards each other. It only has to manage the last
couple of meters.

\/ _| |O
/O
_
O

Besides, the base of the hubble is one big circle with the docking
mechanism in the middle. You can't really get a better bulls eye.

Careful with the terminology. It's a berthing target, not a docking
target.

I'd be happy to use the correct technical words, but NASA likes to keep it's
facts and figures under wraps and dumb down public information. (Try finding
a NASA page about the option C station.) If hubble was launched today they'd
call it the Really Big Digital Camera! I can't help but wonder how quickly
these problems might be solved if the physical tech-specs were publically
available. (If it is I can't find it.) That way we could have a rule book as
to what might/might not be possible, rather having to guess.

And erm, does the joint have to be very strong? It's not going to be taking
more than a few newton's worth of thrust once it's latched on. What's wrong
with using a couple of long rubburised clamps?

The Canadians have been working on such a system (SVS) for over a decade,

Hmm. Not entirely. The SVS works by tracking black dots over a white
background. This would work by tracking a single large shiny white dot over
a very black background, and measuring it's apparent deformation. It would
be a much simplier system and should a similarly simple application of
existing SVS software. This would, however, only be true as long as the side
of the telescope didn't come into view of the camera-sensor. At that point
the system could become very confused, yes.

John

"Jorge R. Frank" wrote:

Not really. "Rendezvous" and "intercept" are two separate problems - with
intercept, the objective is to hit the target hard and destroy it.

Nit: With "intercept" the general idea is to get close enough to the
target that the payload of the interceptor can destroy/disrupt the
target. This is a sufficiently hard problem that most weapons systems
have for decades relied on larger or more clever warheads (I.E.
expanding rod or controlled fragmentation) rather than on direct
impact. (This also has the advantage of allowing time for the fuse to
function, which was a major problem with direct impact weapons.)

IIRC the current BMD interceptor is the first intentional HTK weapon
we have built in quite a long time.

D.
--
Touch-twice life. Eat. Drink. Laugh.

In sci.space.policy John wrote:
"Jorge R. Frank" wrote ...

It is. How do you plan to attach the line, for one? An EVA crewmember
can't
go out that far from ISS; SAFER doesn't carry enough gas and is
zero-fault-
tolerant. It's really just an emergency rescue device, not like the MMU.

Yeah well, that's just an arguement against the use of manned space
stations. If they can't do something as relatively simple as this without
turning it into a horrendously complicated affair...

All you'd need is a glorified pogo stick and a safety cord. You hit hubble
or you don't. If you don't you reel yourself back in and try again. This is
of course a heath robinson approach, and I'm willing to believe there woudl
be technical and safety issues. But I really would like to know why NASA
never uses the space-pencil approach more often.

The serious answer is if it's only a few hundred meters away the space
shuttle can safely grab it without fear of not being able to get to he ISS.

....snip...`

Besides, the base of the hubble is one big circle with the docking
mechanism in the middle. You can't really get a better bulls eye.

Careful with the terminology. It's a berthing target, not a docking
target.

I'd be happy to use the correct technical words, but NASA likes to keep it's
facts and figures under wraps and dumb down public information. (Try finding
a NASA page about the option C station.) If hubble was launched today they'd
call it the Really Big Digital Camera! I can't help but wonder how quickly
these problems might be solved if the physical tech-specs were publically
available. (If it is I can't find it.) That way we could have a rule book as
to what might/might not be possible, rather having to guess.


A good bit of this information may be derived (if not being exactly
listed) in the material at
http://hubble.gsfc.nasa.gov/end-of-mission.html

The latest HST proposal review results are just out - I suppose
we also serve who drive up everyone else's oversubscription rates...

Bill Keel

"John" wrote:

"Jorge R. Frank" wrote ...

It is. How do you plan to attach the line, for one? An EVA crewmember
can't go out that far from ISS; SAFER doesn't carry enough gas and is
zero-fault-tolerant. It's really just an emergency rescue device, not like
the MMU.

Yeah well, that's just an arguement against the use of manned space
stations. If they can't do something as relatively simple as this without
turning it into a horrendously complicated affair...

Because it's only simple when you ignore or handwave away all the
difficulties.

All you'd need is a glorified pogo stick and a safety cord. You hit hubble
or you don't. If you don't you reel yourself back in and try again. This is
of course a heath robinson approach, and I'm willing to believe there woudl
be technical and safety issues. But I really would like to know why NASA
never uses the space-pencil approach more often.

Because the space-pencil approach only works for problems where simple
solutions exist and there are few complications. Not every problem is
so amenable to simplification without handwaving and blinders
willingly donned.

I've assumed the hubble is still active and able to control it's direction.

Bad assumption.

D.
--
Touch-twice life. Eat. Drink. Laugh.

"John" wrote in
news:Efibc.107$is5.0@newsfe1-win:

"Jorge R. Frank" wrote ...

It is. How do you plan to attach the line, for one? An EVA crewmember
can't
go out that far from ISS; SAFER doesn't carry enough gas and is
zero-fault-
tolerant. It's really just an emergency rescue device, not like the
MMU.

Yeah well, that's just an arguement against the use of manned space
stations. If they can't do something as relatively simple as this
without turning it into a horrendously complicated affair...

What you may think is simple is not necessarily what turns out to be simple
once you really start looking seriously at the problem.

All you'd need is a glorified pogo stick and a safety cord. You hit
hubble or you don't. If you don't you reel yourself back in and try
again. This is of course a heath robinson approach, and I'm willing to
believe there woudl be technical and safety issues. But I really would
like to know why NASA never uses the space-pencil approach more often.

Because the space-pencil approach is a myth, an urban legend.

The Myth: "In the 1960s, NASA spent millions of taxpayer dollars developing
a pen that could write in zero-G. The Soviets used a simple pencil
instead."

The Reality: "NASA used pencils for Mercury and Gemini, but found them
unsuitable because the graphite dust posed an inhalation/eye hazard to the
crew, and being conductive, an electrical hazard if it drifted behind
control panels. The wood was also a fire hazard in an all-oxygen
atmosphere. The Fisher Pen Co., learning of NASA's problem, developed the
Fisher Space Pen with its own corporate funds and sold pens to NASA at
commercial rates. The Soviets also adopted the Fisher Space Pen in 1968."

If the pogo-stick and safety-cord approach were really analogous to the
space-pencil myth, then why have the Soviets/Russians never attempted
anything like it in their three-plus decades of space station operations?

The serious answer is if it's only a few hundred meters away the space
shuttle can safely grab it without fear of not being able to get to he
ISS.

The more serious answer is that NASA doesn't allow three-body prox ops with
the shuttle unless two of the bodies are manned and maneuverable, and even
then, under extraordinary precautions (c.f. STS-71 undocking, 1995). The
OTV would be placed far outside prox ops range, probably around 40 n.mi. or
greater, along the plus or minus Vbar.

The OTV won't keep going perfectly forward due to orbital mechanics,
which causes some decidedly non-intuitive effects in LEO. The OTV
must have the capability to constantly correct its lateral alignment
as it approaches.

I've assumed the hubble is still active and able to control it's
direction.

You are confusing rotation about the center of mass with translation of the
center of mass. I am saying that the *OTV* will not keep going in a
straight line. It does not matter how accurately HST can point, because it
cannot translate to match the OTV.

And the assumption that HST will still be able to control its direction is
a poor one. By 2007-08, HST is expected to have lost most or all of its
remaining gyros, and will downmode to "zero gyro sun-pointing" mode. In
this mode, HST is no longer capable of accurate pointing, though attitude
rates should be relatively benign ( 0.22 deg/sec per axis in all three
axes).

Besides, the base of the hubble is one big circle with the docking
mechanism in the middle. You can't really get a better bulls eye.

Careful with the terminology. It's a berthing target, not a docking
target.

I'd be happy to use the correct technical words, but NASA likes to
keep it's facts and figures under wraps and dumb down public
information.

(Try finding a NASA page about the option C station.) If
hubble was launched today they'd call it the Really Big Digital
Camera! I can't help but wonder how quickly these problems might be
solved if the physical tech-specs were publically available. (If it is
I can't find it.) That way we could have a rule book as to what
might/might not be possible, rather having to guess.

I hope you found William Keel's URL enlightening.

The Canadians have been working on such a system (SVS) for over a
decade,

Hmm. Not entirely. The SVS works by tracking black dots over a white
background. This would work by tracking a single large shiny white dot
over a very black background, and measuring it's apparent deformation.
It would be a much simplier system and should a similarly simple
application of existing SVS software.

Not exactly. The apparent deformation only gives the magnitude of the
misalignment, not the sign. To discern the sign, the system would need to
be more sophisticated than simply measuring an oval.

This would, however, only be
true as long as the side of the telescope didn't come into view of the
camera-sensor. At that point the system could become very confused,
yes.

It will also get very confused every time the sun causes a specular
reflection off HST's surface and causes the camera to "bloom". It will also
get very confused when its own shadow passes over HST and blacks out the
part of the telescope it's approaching.

That's not to discourage you from solving the problem, of course. If you
succeed, you will become very famous in aerospace circles, and probably
quite rich as well. :-)


--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
think one step ahead of IBM.

"Jorge R. Frank" wrote:
It will also get very confused every time the sun causes a specular
reflection off HST's surface and causes the camera to "bloom". It will also
get very confused when its own shadow passes over HST and blacks out the
part of the telescope it's approaching.

What about some inspiration from residential infrared remote controls ?

Your VCR doesn't go nuts when the sun shines on it, even though it gets plenty
of infrared in its reader. It is looking an oscillating IR signal and filters
out "ambiant" IR.

Couldn't they do something like this where they could have some strobe going
on at a very specific rate, and then software that could remove ambiant light
from images by calculating the difference in the image when the light is off
and when the light is on ?

This would then enable approaches in darkness and in light.

"Jorge R. Frank" wrote ...
What you may think is simple is not necessarily what turns out to be
simple
once you really start looking seriously at the problem.

NASA however has had 20 years to seriously look at the problem and has
proposed some serious solutions. It hasn't implimented any of them yet. I
can't help but compare NASA's performance with it's russian counterparts.
You say the space pencil story is a myth. What about the one about the
americans spending billions on the Freedom/Alpha/ISS whilst the russians
just built 7 Salyuts and a Mir? You must admit that NASA does, on rare
occasion, tend to over think some tasks. And you can't blame that entirely
on congress.

The Myth: "In the 1960s, NASA spent millions of taxpayer dollars
developing
a pen that could write in zero-G. The Soviets used a simple pencil
instead."

Aww! You spoil all my precious childhood stories.

If the pogo-stick and safety-cord approach were really analogous to the
space-pencil myth, then why have the Soviets/Russians never attempted
anything like it in their three-plus decades of space station operations?

Probably because they never needed to. When Russians intended things to
attach to each other they made them so such operations would be relatively
easy, and wouldn't require significant onsite human involvement. Pity NASA
couldn't have built Hubble with a big heavy 'grab here' hardpoint on it's
backside.

The more serious answer is that NASA doesn't allow three-body prox ops
with

The OTV would need an autodocking facility then. Progress modules have this
capacity, and this is the basis for my 'back of the envelope' design.

And the assumption that HST will still be able to control its direction is
a poor one. By 2007-08, HST is expected to have lost most or all of its

I wouldn't wait so long. A crash-built OTV could be launched way before
then. If it fails then you learn a lot about OTV design before it burns up
and you fall back on the current plan. NASA could also honestly said they'd
tried. If it works you keep hubble, learn a *lot* about OTV design and get a
new long-term toy for NASA to play with.

Not exactly. The apparent deformation only gives the magnitude of the
misalignment, not the sign. To discern the sign, the system would need to
be more sophisticated than simply measuring an oval.

Ah, good point. For this and other reasons I conceed this would be much
harder than I first thought. Especially after looking at those technical
drawings. None of the other images I've sen of hubble make it look quite so
cluttered. Still, no reason to give up. ^.^

John
-And here's your pinch of salt.

"William C. Keel" wrote

A good bit of this information may be derived (if not being exactly
listed) in the material at
http://hubble.gsfc.nasa.gov/end-of-mission.html

Ohhh - pretty!
Thanks for this!

Don't suppose anyone knows if there's anything similar for soyuz/progress?

John