Posted by Ed Cheng on December 16, 1999 at 12:54:36:
In Reply to: Hubble Gyroscopes posted by Keith Rosenberg on December 16, 1999 at 10:38:36:
> A colleague of mine and I were discussing the Hubble gyroscopes. And it came to my attention that they were wearing out much sooner than might be expected. This implys mechanical Gyros. Since laser gyros are far more reliable and sensitive than mechanical gyros, the presence of mechanical ones is a little strange.
> Are the gyros used to micro adjust the attitude of the Hubble when it is in operation?
> Keith B. Rosenberg
> enorton2@ix.netcom.com
Indeed they are mechanical gyros. They are, in fact, the world's most
sensitive and stable gyros. Laser gyros are fine for many things, but
they do not have low enough noise for Hubble. We have also looked at
hemispherical resonating gyros. We almost got some of these to work
at Hubble's accuracies, but we fell short in noise by about a factor of 2.
The gyros are used to control Hubble over time scales of a few seconds or
less. The fine guidance sensors make sure that Hubble is points fixed
in the sky relative to the stars, but they only work on time scales of a
few seconds or longer. Thus, the gyros are used as "interpolators", as
well as during times when we do not see the star (when we are behind the
Earth) and when we are moving from one position to another.