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Wednesday, October 23, 2019

Space Bearings

Scientists May Have Figured Out Why So Many Spacecraft Were Failing

I knew that you could use flywheels driven by electric motors to control the attitude of a spacecraft, and I sort of knew that it was being done. It didn't seem like a really great idea because if you don't want the spacecraft's attitude to change, you need to make sure you aren't exerting any torque on the flywheels, except that won't work unless you have frictionless bearings and I'm pretty sure those don't exist. I suspect that even super low friction bearings like magnetic, or air, or fluid exert some drag, so you are going to need a motor that can supply the very low amount of torque needed to counteract that drag. So as long as you want the spacecraft to point in a specific direction (maintain the correct attitude: stand up straight, chin up, suck in that gut), you are going to need to supply the motor with power. It won't need much, but it will be a constant drain on your supply. Won't matter so much if you have solar panels, but for voyages out to Jupiter and beyond, solar panels won't cut it. Those guys use nuclear power mostly, so maybe it isn't an issue.

Anyway, Scott does a good job of explaining the issue and what may have caused it. The thing I don't get is just what impact a big solar flare would have if you were to encounter it. For people it can be very bad, but for mechanical devices? I wouldn't think it would have much effect. But maybe I'm wrong.

I remember reading an science fiction story once upon a time where big spaceships used reaction wheels to control their attitude. One spaceship set down on a planet, but one of its three landing legs did not deploy, but it had these powerful reaction wheels, so it was able to continue standing up straight even though it only had two legs. The pilot should have noticed this, but he was riled up over some disagreement and went charging off to resolve it. The reaction wheels kept the spacecraft standing for a while, but the strain was more than they were designed for so in short order the bearings froze and the spacecraft went cartwheeling across the landscape. Oops.

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