Malfunctioning Gyroscope on ISS shut down

"John Doe" wrote in message ...
Jim Oberg wrote:
Retrieving worn-out CMGs is another problem post-shuttle, but here
I suspect inflatable down-cargo canisters will quickly step in.

Quickly ?????


NASA is not even near even thinking about such a concept. They don't
even have any real/serious/funded plans for the equivalent of a progress
to automatically get to station and dock. (and they'd want that ASAP so
any fittings can be installed on PMA2 before shuttle stops flying. It
won't happen.

Just because NASA lacks the "vision" does not mean that such a vehicle isn't
possible. You could fund this one as an X-prize sort of contest. The first
person to demonstrate a vehicle that can accomidate a CMG size weight dummy
payload and safey return it to earth from LEO wins a prize of X US dollars.

Broken CMGs are more likely to be attached to the station with Tie-Wraps
for eternity rather than to have some survivable re-entry.

After someone wins the contest mentioned above, contract with them to return
the failed CMG.

There are a lot fo aspectes of the station which are going to be
severely disrupted by the loss of the shuttle.

The only one I can think of is return of large payloads (like the CMG).
Progress, ATV, HTV, and commercial access to the station ought to take up
most of the shuttle slack. Even the CEV ought to be able to take up some
slack. Manned it's a Soyuz replacement. Unmanned it's a Progress/shuttle
replacement that can return small payloads to earth, such as experimental
results.

And NASA should really
come forth with their concrete plans and ideas. Otherwise the assumption
should be that NASA will just abandon the USA segment and stop
replenishing it with O2 and stop sending any replacement part that
cannot fit through a russian hatch. (progress or ATV).

Pesky international agreements, right John?

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)

On Oct 12, 9:21 pm, "Jim Oberg" wrote:
The CMG can't fit through the Russian segment hatches so the ATV is out.
However, the Japanese HTV is designed to mate with the CBM and its
big door
Taking the CMG inside seems like something you want to avoid, since
that means you have to get it out of the airlock again.

Based on this http://www.jaxa.jp/jda/brochure/img/01/htv.pdf it looks
like HTV has significant capability to carry unpresurized cargo. If a
CMG fits (which from the graphic looks pretty likely), this would seem
ideal since it's within reach of the canadarm.

On a slightly different topic, it seems that gyros, reaction wheels
etc. in space have a high premature failure rate. Figuring this out
seems like one of the engineering lessons we should be learning on ISS
to prepare for future exploration.

hop wrote:
[...]
Taking the CMG inside seems like something you want to avoid, since
that means you have to get it out of the airlock again.

Maybe talk to Mr Big ..er, Bigelow... about an orbital workshop with a
big garage door? Zippers might be a little inadequate to seal a big
hatch on an inflatable, but maybe his team has some alternate ideas.

Then deflate, put it behind a foam block to deorbit, and rent it out to
the Chinese.

/dps

The wheel weighs 218 lbs and spins at 6600 rpm, producing 3500 ft-lb-s
of angular momentum. I'm too lazy to turn that into joules, but
there's enough info there if you want to.

It is not possible to provide enough current to the CMG for the wheel
to spin fast enough to break apart. It's a solid steel wheel and
would have to more than double its operational speed to do that.



On Fri, 13 Oct 2006 12:48:33 +1000, Chris Bennetts
wrote:

John Doe wrote:

In terms of the vibration: how much energy do those wheels store ? Is
there a danger that the casing would not fully contain a flywheel
breaking apart ?

Possibly, if the failure was violent enough.

So, which would be easier now ? Outfit a progress to carry a CMG and a
fake docking port ahead of it ?
Outfit ATV in a similar fashion ?

I'd bet that an extra shuttle flight would be cheaper than either of
those options.

Could they just stick a CMG on a progress and have the progress station
keep close enough to be grappled by the station arm, at which point an
EVA can travel along teh arm to the progress, fetch the CMG, bring it to
Z1, and then bring the failed CMG to the progress, fasten it, and then
let Progress go away and deorbit ?

Such work would require very tight manoeuvring of the Progress via
remote control. That would be extremely difficult, with a high
probability of the Progress colliding with the station. They wouldn't
risk it.

--Chris

Based on this http://www.jaxa.jp/jda/brochure/img/01/htv.pdf it looks
like HTV has significant capability to carry unpresurized cargo.

Right. Look at the parts called "unpressurized carrier" and "exposed
pallet".

I'm not sure whether we established, last time this subject came up on
these newsgroups, whether a CMG could be delivered in this way. But
it did seem like the obvious first place to look.

Now, if you want to return the broken one for refurbishment, sure the
problem gets more complicated. But I'd be pretty surprised if that
were cost-effective anyway (cue standard flamewars about which costs
to count...).

Jim Kingdon wrote:
[...]
Now, if you want to return the broken one for refurbishment, sure the
problem gets more complicated. But I'd be pretty surprised if that
were cost-effective anyway (cue standard flamewars about which costs
to count...).

As others have said, the post-mortem inspection may be more valuable
than the refurbished item. So far, we don't have a good way to do that
job in LEO.

/dps

Now, if you want to return the broken one for refurbishment, sure the
problem gets more complicated. But I'd be pretty surprised if that
were cost-effective anyway (cue standard flamewars about which costs
to count...).

You may want to examine the broken one on the ground in the lab to
figure out what exactly failed. But I doubt that you'd fly it again.
Given the other costs, a brand new one wouldn't be significantly more
expensive anyway. Sure you could just toss it out the airlock, but
we're trying to cut down on space junk.

You may want to examine the broken one on the ground in the lab to
figure out what exactly failed.

I'll grant that. Now it doesn't seem like this capability is likely
to exist beyond 2010 (at least, if a CMG is too big to fit in one of
the reusable alt.space vehicles which may or may not be the most
likely possibilities), but I will admit that this makes more sense
than going to all the trouble with the the idea of saving money.

Sure you could just toss it out the airlock, but we're trying to cut
down on space junk.

Probably not a particularly big deal. Small enough to burn up
(mostly, although the flywheel could be an issue). Big enough to
track by radar. Stays in one piece (I'm assuming....). In an orbit
where it won't be there for more than a few years.

Chris Bennetts wrote:
George R. Kasica wrote:
To the experts out there....

1) what are the effects of just one gyro running during the space
walk/docked ops?

The remaining gyro will have to be augmented with Russian segment
attitude thruster firings to maintain the station's orientation.

2) Can they repair or replace the failed unit assuming it can't get
spun up again??

Another CMG was replaced on STS-114 last year. The only suitable flight
coming up would be ISS-13A.1 (STS-119?), but that's pretty packed. The
manifest is very tight, and gyroscopes are heavy, so flying a
replacement could push an extra logistics mission into the schedule.

The CMGs appear to be less reliable than hoped. I wonder if NASA will
fly one or two extra CMGs up on a late shuttle flight to be used as cold
spares.

--Chris

In sci.space.station Jeff Findley wrote:

"Craig Fink" wrote in message
news
Well, if the CMG is properly designed, it should only take one.

With the little experience we have with CMG's in LEO, how can one expect a
team of engineers to "properly" design one? It's the unknown unknowns that
bit you!

Well...
If it was me, I'd be putting nearly all the crap like CMGs, inside the
pressure cabin.
If it needs vacuum, you have a vacuum line to a suitable place.
Then you do turn off the vacuum line, open the box, and fiddle with it.

If it breaks, you stick it in the trash pile in the corner.
(bolted to the trash-frame of course)

But I'm not designing these things.
(yes, this is a ET station)