Space Forum / Shuttle / November 2007

Just because an object is in orbit does not necessarily mean that its
orientation is fixed with respect to the earth, it's path around the earth,
and etc.  But it is noted that objects in earth orbit do encounter forces
which do tend to change their orientation.  These include gravity, drag
(there is still a tiny bit of air up there), magnetism (earth's magnetic
field), solar effects, and etc.  So, in light of all of these forces, Hubble
needs a way to counteract them.

To this end, Hubble has an extremely sensitive pointing system, so it can
remain pointed at a target for very long periods of time, which enables it
to take very long exposure pictures.  You ought to be able to find more info
about this system by Googling for "Hubble gyroscopes " or something like
that.

Jeff

If you look sideways out of your moving car at a distant building, you dont
have to move your head as the object stays in the same direction. The
further away it is the longer it seems to stay in the same place. Hubble is
looking at objects millions of miles away so will appear in the same point
of space even though Hubblle is moving around 8000 miles in either
direction.