Hubble's rate sensors

In article ,
mvillanu wrote:
Were these mechanical gyros more accurate than solid-state gyros?

There were no good solid-state gyros at the time Hubble was designed.
Remember, this is 1970s hardware -- Hubble was originally supposed to fly
in 1981 or thereabouts. Ring-laser gyros were coming along, but if memory
serves, weren't there yet... and they still had moving parts.

(Ring-laser gyros have a weak tendency for the output to "stick" at zero
when rotation rates are very low, due to backscattering coupling their two
opposing beams together. Much the most successful fix for this, alas, is
to wiggle the whole gyro back and forth -- "dithering" -- so the rotation
rate is always substantial.)

The solid-state gyro technologies also have difficulty meeting the specs.
No, I don't know the exact HST numbers, but I do know they're demanding...
and the solid-state-gyro technologies tend to yield low-end devices,
suitable only for limited requirements. This is changing, but slowly.

Their MTBF doesn't seem too impressive...I'm just wondering why they
didn't use a more robust rate sensor.

Why they didn't use some other flavor of mechanical gyro, I'm not sure;
probably this one just looked good at the time.

Solid-state gyros have only recently gotten good enough to be competitive.
The first fiber-optic gyros in space were on Clementine, in 1994, and that
was explicitly a technology demonstrator. I think the first "operational"
use of solid-state gyros in space was the hemispherical-resonator gyros on
NEAR, launched in 1996.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |