Update: Gyro shutdown no threat to shuttle visit; oxygen reserves also in good shape

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Update: Gyro shutdown no threat to shuttle visit; oxygen reserves also in
good shape

The shutdown of an orientation control gyroscope aboard the international
space station will not impact the planned launch of the shuttle Discovery in
May, officials said today, even though only two of the lab's four gyros will
be operating when the orbiter arrives.

Station program manager Bill Gerstenmaier also said the loss of control
moment gyroscope No. 2 early Wednesday would not prevent Discovery's crew
from making worst-case repairs to the orbiter after docking if the ship's
heat shield tiles or wing leading edge panels were damaged during launch.

If such repairs were actually needed, the shuttle might have to be
re-oriented using the ship's robot arm to give spacewalking repairmen access
to hard-to-reach areas. While that would be more difficult with just two
operational gyros, Gerstenmaier said station stability could be maintained
using Russian rocket thrusters instead.

And in any case, a new CMG will be installed during Discovery's visit to
replace one that failed in 2002, once again giving the station three
operational gyros. When CMG-2's faulty circuit breaker eventually is
replaced, the lab complex will once again have four operational CMGs.

Gerstenmaier said flight planners are studying the timelines for the three
shuttle spacewalks to determine if it might be possible for Discovery
astronauts Stephen Robinson and Soichi Noguchi to install a fresh remote
power control module during one of their excursions.

Mike Fincke, who spent six months aboard the station last year, installed
the unit that failed Wednesday during a spacewalk last summer. He said today
it would probably take Robinson and Noguchi about an hour to complete the
swap out if time was available.

But the Discovery spacewalk timelines already are tight and it appears more
likely the space station's crew will be asked to replace the unit during a
spacewalk after Discovery departs.

Gerstenmaier said the power control module has 17 channels and that a
suspect transitor believed to be susceptible to failures in identical
devices used throughout the station apparently caused the gyro circuit to
trip open Wednesday. An identical failure knocked CMG-2 off line last year,
requiring Fincke and Expedition 9 commander Gennady Padalka to replace the
unit last summer.

Gerstenmaier said engineers are developing a new design to eliminate the
transistor problem and that in the meantime, he viewed the most recent
failure as a relatively minor glitch.
Overall, he said, the space station is in good shape for Discovery's return
to flight in mid May. Over the past few days, engineers have been
troubleshooting recurring problems with the station's Russian Elektron
oxygen generator. But Gerstenmaier said even if the unit failed today and
could not be restarted, enough stored air is available to support
Discovery's launching and to support both crews in a "safe haven" mode if
shuttle damage forced NASA to launch a rescue mission.

As of today, with the Elektron in operation, the station has enough air to
support both crews for at least 45 days, which NASA says is long enough to
get another shuttle to the station in an emergency. A total Elektron failure
in the immediate future would cut into those reserves, but Gerstenmaier said
enough would be available for safe haven.

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Jacques :-)

www.spacepatches.info

Will this have any effect on the "EVA mystery torque"?

Good question. You are referring to venting, from the suit's thermal
control system,.that puts a torque on the station during EVAs. A rather
serious issue that arose was during the last EVA when a thruster fired.
NASA was not convinced that the Russian controller was aware of the
actual position of the astronauts. The positioning thrusters contain
toxic propellants and suit contamination is a concern. Meetings were
held, and everyone was equally dissatisfied, and so the issue is now
resolved until next time. Since two gyros and the positioning thrusters
are available for use during the EVA, I expect that any effects from the
mystery torque will be dealt with routinely.

"Revision" wrote in message
...

Will this have any effect on the "EVA mystery torque"?

Good question. You are referring to venting, from the suit's thermal
control system,.that puts a torque on the station during EVAs. A rather
serious issue that arose was during the last EVA when a thruster fired.
NASA was not convinced that the Russian controller was aware of the
actual position of the astronauts. The positioning thrusters contain
toxic propellants and suit contamination is a concern. Meetings were
held, and everyone was equally dissatisfied, and so the issue is now
resolved until next time. Since two gyros and the positioning thrusters
are available for use during the EVA, I expect that any effects from the
mystery torque will be dealt with routinely.



But will there be any impact on thruster fuel reserves, for example?

JJ Robinson II
Houston, TX

At the pre-EVA press conference, they said it would shorten the time
that the CMGs could resist the torque, from just under an hour
to about half an hour. at that point they will just go 'free drift', they
will
NOT use thrusters to maintain attitude, and they expect to pitch (up
or down, they're not sure which) for the next three hours until the
crew gets back to a 'safe zone' where they can rest while the
thrusters are activated. The degree of attitude error will only
impact the TIME required to rotate back into alignment at a
standard rate, so it will NOT impact prop usage.



"JJR2" wrote in
"Revision" wrote
Will this have any effect on the "EVA mystery torque"?

Good question. You are referring to venting, from the suit's thermal
control system,.that puts a torque on the station during EVAs. A rather
serious issue that arose was during the last EVA when a thruster fired.
NASA was not convinced that the Russian controller was aware of the
actual position of the astronauts. The positioning thrusters contain
toxic propellants and suit contamination is a concern. Meetings were
held, and everyone was equally dissatisfied, and so the issue is now
resolved until next time. Since two gyros and the positioning thrusters
are available for use during the EVA, I expect that any effects from the
mystery torque will be dealt with routinely.



But will there be any impact on thruster fuel reserves, for example?