News f2s wrote:
"Jeff" wrote in message
news
News f2s wrote:

"Jeff" wrote in message
...


BTW, I learned celestial navigation while working on a craft
that used gyros for stabilization. When the gyros failed, the
craft was scuttled!


Did it use the gyros to hold the craft rigid? or did it use
them to drive stabiliser vanes to counter roll?

The gyros were used directly to keep the craft at the correct
attitude. There were six onboard when launched, and they failed
one by one. When they all died, it was abandoned and scuttled.
BTW, the cost of the craft was $250,000,000, 28 years ago.


I guess they had to use an even number, half rotating one way, and
half rotating the other, to cancel precession. What a project!

The "craft" was the Einstein Observatory, and orbiting x-ray
telescope. The gyros are called CMG's, control moment gyros -

"a gyroscope, usually much larger than a gyro sensor, mounted on a
single or double gimbal and used to generate control torques. The
torques are generated by commanding gimbal angle rates that result in
inertial motion of the CMG spinning wheel and accompanying gyroscopic
reaction torques on the vehicle structure."

IIRC, they decided to save a few mil by not including magnetic torque
rods, which would torque against the Earth's magnetic field to
maintain stability.

Sailing content: The previous x-ray telescope was placed in a lower
orbit, and as the orbit decayed it started bouncing against the
atmosphere. The controllers (clever MIT grad students) oriented the
solar panels so it would surf on the atmosphere, and extended its
useful life by several months. OK, its more like water skiing than
sailing.