Half of remaining ISS gyros exhibiting stress

ISS continues to limp along on two CMGs,
[both broken ones will be replaced/repaired on
the Return-to-Flight STS-114 mission],
but one of the good ones appears to be experiencing
more and more frequent 'hiccups'.

From today's On-Orbit Status Report, "The ISS CMGs
(control moment gyros) have experienced at least one
torque event each day over the weekend. These events,
which consisted of gimbal rate reactions (response to
a disturbance) without elevated spin motor currents or
vibration, appear to correspond to RED exercise periods."

It seems odd that these heavy gyros would be sensitive
to the crewmembers banging around with their RED
(Resistive Exercise Device -- a space 'Boflex'), but
if so, prudent and gentle operations are called for.

There is enough propellant for control with Russian
thrusters, and some ingenious gravity-gradient-type
station attitudes have been certified (in terms of
power generation and thermal loads), so the ISS
ground controllers are ready to implement backup
plans if (or when) the third CMG fails.

It's always something, as Rosanne Rosanadana says...

Jim Oberg wrote:

It seems odd that these heavy gyros would be sensitive
to the crewmembers banging around with their RED
(Resistive Exercise Device -- a space 'Boflex'), but
if so, prudent and gentle operations are called for.


The repetitive motions of the device maybe exciting a resonant frequency
in the station sufficiently to stress out the CMGs? Sounds like a fun
harmonic analysis...

In some ways, the most interesting research results will be discovering
the secondary effects in a large space structure. We understand many of
the obvious issues (use good seals on the hatches, plan for
field-replaceable components, etc), but seem to be learning a lot more
about things like building ammonia-line connectors, management of widely
separated command centers, and the ability of seemingly minor influences
(space-suit sublimators, exercise equipment) to perturb a large space
structure sufficiently to become a problem.

--
Reed Snellenberger
GPG KeyID: 5A978843
rsnellenberger-at-houston.rr.com

On Mon, 11 Apr 2005 20:42:13 +0000, Reed Snellenberger wrote:

Jim Oberg wrote:

It seems odd that these heavy gyros would be sensitive
to the crewmembers banging around with their RED
(Resistive Exercise Device -- a space 'Boflex'), but
if so, prudent and gentle operations are called for.


The repetitive motions of the device maybe exciting a resonant frequency
in the station sufficiently to stress out the CMGs? Sounds like a fun
harmonic analysis...


Which raise the question, which one? Who was on the treadmill? Tell him to
speed up or slow down.


--
Craig Fink
Courtesy E-Mail Welcome @

Reed Snellenberger wrote:
The repetitive motions of the device maybe exciting a resonant frequency
in the station sufficiently to stress out the CMGs? Sounds like a fun
harmonic analysis...


The station has been up in this configuration for many years.. This crew
with its exercise regimen has been up for close to 6 months. If this CMG
"hiccup" starts now, it can't really be blamed on the crew.

If normal living activity can't be handled by the CMGs when they used to
handle it without problem in the past, then there is something wrong
with the CMGs.

NASA has said it could survive on only 2 CMGs,. perhaps the stress of
normal daily life is too much for only 2 CMGs.

Craig Fink wrote:

Which raise the question, which one? Who was on the treadmill? Tell him to
speed up or slow down.

My first thought as well, but Jim's note specifically refers to the
Resistive Exercise Device (RED), not the treadmill (whose acronym is
TVIS). It's a significant difference, since the whole point of the
fancy treadmill is to eliminate a significant source of vibration.

I can easily imagine an engineer looking at the "space Bowflex" and
concluding that there's *no way* a guy pulling on cables (even a driven
astro-guy who *always* does his Bowflexing at a constant frequency of
1.75 Hz) could screw up the dynamics of a 450 metric ton space station.

--
Reed Snellenberger
GPG KeyID: 5A978843
rsnellenberger-at-houston.rr.com

On Tue, 12 Apr 2005 03:26:27 +0000, Reed Snellenberger wrote:

Craig Fink wrote:

Which raise the question, which one? Who was on the treadmill? Tell him
to speed up or slow down.

My first thought as well, but Jim's note specifically refers to the
Resistive Exercise Device (RED), not the treadmill (whose acronym is
TVIS). It's a significant difference, since the whole point of the
fancy treadmill is to eliminate a significant source of vibration.

I can easily imagine an engineer looking at the "space Bowflex" and
concluding that there's *no way* a guy pulling on cables (even a driven
astro-guy who *always* does his Bowflexing at a constant frequency of
1.75 Hz) could screw up the dynamics of a 450 metric ton space station.


1.72 Hz or is that .5 Hz is a pretty low frequency, large things have low
resonance frequencies. I would have thought they would have seen it in the
gyro data when it started to fight a resonate frequency. Since it hasn't
been seen before, I would think it has something to do with something that
moves and may have shown up because because of the orbit to sun geometry.
Or, maybe they change the location of the RED. If something is getting
excited, the CMG might be the least of their problems. What ever
is getting excited could loaded beyond its design limit. Like that pilot in
New York who broke the tail off his aircraft.

Ever bounced an elevator? It's kind of fun, the resonance frequency is easy
to find, and it's usally pretty high, very small hops are required to get
the elevator bouncing quite a bit. Plus as the spring (cable) get's
shorter the frequency changes. It's best to do this when you have the
elevator to yourself as all the other passengers will quickly get
annoyed and put you out on the wrong floor.

--
Craig Fink
Courtesy E-Mail Welcome @

Crew exercise has always been detectable by looking at the torque
commands for the CMGs. In fact, that is often how the ground can tell
that the crew is awake.

Crew exercise is not a problem for healthy CMGs to absorb.

The frequency is not an issue.

The ISS is currently down to two active CMGs (and one of those is
flaky) and thus the MER has put pretty strict guidelines on how those
CMGs should be used until a replacement is sent up and an autopsy is
done on CMG 1.








On Tue, 12 Apr 2005 03:26:27 GMT, Reed Snellenberger
wrote:

Craig Fink wrote:

Which raise the question, which one? Who was on the treadmill? Tell him to
speed up or slow down.

My first thought as well, but Jim's note specifically refers to the
Resistive Exercise Device (RED), not the treadmill (whose acronym is
TVIS). It's a significant difference, since the whole point of the
fancy treadmill is to eliminate a significant source of vibration.

I can easily imagine an engineer looking at the "space Bowflex" and
concluding that there's *no way* a guy pulling on cables (even a driven
astro-guy who *always* does his Bowflexing at a constant frequency of
1.75 Hz) could screw up the dynamics of a 450 metric ton space station.

Crew exercise has always been detectable by watching the torque
commands to the CMGs.

Crew exercise is not a problem for healthy CMGs.

ISS is down to two active CMGs, right now - and one of those is flaky
- and the MER has put pretty strict usage guidelines on those CMGs
until they can get a replacement up there and do an autopsy on CMG1
(or 3, whichever they choose to replace).





On Tue, 12 Apr 2005 03:26:27 GMT, Reed Snellenberger
wrote:

Craig Fink wrote:

Which raise the question, which one? Who was on the treadmill? Tell him to
speed up or slow down.

My first thought as well, but Jim's note specifically refers to the
Resistive Exercise Device (RED), not the treadmill (whose acronym is
TVIS). It's a significant difference, since the whole point of the
fancy treadmill is to eliminate a significant source of vibration.

I can easily imagine an engineer looking at the "space Bowflex" and
concluding that there's *no way* a guy pulling on cables (even a driven
astro-guy who *always* does his Bowflexing at a constant frequency of
1.75 Hz) could screw up the dynamics of a 450 metric ton space station.

On Tue, 12 Apr 2005 23:30:35 +0000, R Frost wrote:

Crew exercise has always been detectable by watching the torque
commands to the CMGs.

Crew exercise is not a problem for healthy CMGs.

ISS is down to two active CMGs, right now - and one of those is flaky
- and the MER has put pretty strict usage guidelines on those CMGs
until they can get a replacement up there and do an autopsy on CMG1
(or 3, whichever they choose to replace).



That's interesting, I wonder if the data has a high enough fidelity to see
one of the crew get up in the middle of the night to use the head? What
about downmodes? Really sounds like they only have 1 1/2 CMGs right now.


Craig Fink
Courtesy E-Mail Welcome @

Craig Fink wrote:
1.72 Hz or is that .5 Hz is a pretty low frequency, large things have low
resonance frequencies.

Ever bounced an elevator?


On the station, if a person jumps up, he pushed the station down. But
when his head hits the ceiling, he pushed the station back up. So the
net result on the CMGs should be nil. The CMG may work to counter the
original push, but when they counter the head hitting ceiling, it will
bring the CMG back to where it was prior to the jump.

Adding delayed reaction to the CGM might be able to greatly reduce their
workload since much of the crew exercises would cancel themselves before
the CGMs acted.

The minute you agree that 0g "science" isn't a goal and that testing of
living in 0g (including ECLSS hardware etc) is the goal, then vibration
free environment isn't important anymore.

You may need vibration free environment if the crew are paid to watch
crystals grow in a test tube. But you don't need vibration free
environment to study ways to make equipemment such as Elektron reliable
in 0g.