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Space Station Gyro Problem Dangerous?
mysterystevenson writes "After bringing more mass than ever before up to the ISS, one of the gyros has failed. Gyros help maintain attitude position in space; the more mass needed to be controlled, the more force that is exerted on the gyros. Now there is the danger that the Shuttle may be bringing yet more mass and starting construction while turning off another gyro, which could cause a need for thrusters to maintain attitude. The assemblies are not all constructed to be able to withstand such force and in a bad situation there could be a collapse which could affect the Shuttle and the ISS as well. Worse case could be total loss; a wise idea might be to alter the construction schedule and address the Gyro and Gyro design problems, before going forward with the introduction of more mass."
STOP MAKING ME HUNGRY!
It's only 11:00, the gyro cart won't be out for another hour!
This seems rather alarmist. First off, why would they risk destroying the station to preserve the attitude? It seems that letting it turn somewhat for a limited amount of time would be far better than risking its destruction to preserve its orientation at all costs.
And the time would be limited. Remember, there is conservation of angular momentum. If you are tumbling, you will need to use the thrusters to stop it in any case (gyros don't create or destroy angular momentum--if you want to get rid of some permanently, you'll need to cast off some reaction mass). But for what they do do, which is reorienting a ship by temporarily holding some angular momentum, they can be used as slowly as you want. Heck, if you weren't in a hurry you could turn the ship by hand (actually, foot) by just "walking" around the outer wall without any gyros at all.
--MarkusQ
Thank goodness they have such a renowned inertial theoritician to alert them to this problem. It's just lucky for all of us that he took time away from work adapting massage devices for use as space propulsion devices. When will NASA learn to stop relying on those empty pieces of paper that their engineers call PhD's and start listening to people who've been interviewed by their local media at some indeterminate point in the past and now maintain a wiki.
"Don't you know you're going to shock the monkey?"- Peter Gabriel
ISS is not in imminent danger. First off, it can hold attitude indefinitely on two of four gyros. Second, the solar arrays can withstand the RCS thrusters firing, they just need to lock down the assemblies that rotate the solar arrays first. Therein lies the rub.
The next shuttle mission brings up more parts and re-wires a large section of the ISS's power grid. This means bringing some systems offline for the duration of a spacewalk, reconfiguring them, and bringing them back up shortly thereafter. Naturally, during this process, the ISS will be running on less redundancy than it is now. One of the spacewalks is slated to bring down two of the gyros, on the assumption that the other two can maintain attitude, while running off the new solar arrays which must rotate in order to generate the specified amount of power. Without the other gyro, RCS firings might be necessary, which make the solar cells unhappy.
This is a nontrivial but solvable problem. Solutions currently being proposed:
- Bring up the failing gyro for the duration of the spacewalk. It didn't up and die one day -- it's just vibrating a lot, and might do the trick.
- Leave the failing gyro off, and be prepared to bring it up only if the one operational gyro can't maintain attitude.
- Lock the solar array into a suboptimal orientation, and fire the RCS thrusters as necessary.
- Bring up a replacement gyro. They're about 800 pounds and aren't simple to install, which is a lot to be adding to a mission three weeks from launch, so this is unlikely.
They are rocket scientists, you know.