Re:The remaining wheels are still used (Score 2)

Thanks for the extra info!

It turns out that although the torquer bars are not designed for fine control (their control bandwidth is 15 times lower than the reaction wheels), the satellite is also heavy compared to the MTB's torque. So, the pointing stability is in fact quite good, and the jitter is not much worse than what we had before... as long as the satellite is not pointed in a part of the sky where gravity gradient disturbances are strong.

An oversight on my part ;-) I have only worked on the smaller variants of satellites (100kg to 500kg) - dwarfed by the FUSE of course! The smaller sized S/C poses interesting problems at times. E.g. on one satellite the imager had its own stepper moter used to rotate the optics to enable stereo imaging (scanning the earth's surface from different angles). The dynamics of the small stepper moter had to be considered in the control loop as it had a gyro effect on the rest of the S/C due to the satellites relative small size (about 80kgs if I recall correctly)!