This is the method used for most observations on Astro-1. Here the astronauts
use the guide stars identified in the HUT TV camera field of view to keep the
target centered in the HUT aperture using the manual pointing controller, just
as a ground-based observer would use a button-box or joy stick to guide the
telescope during an observation. When guide stars were available, the crew
on Astro-1 did an excellent job of maintaining pointing stability. For most
observations the rms pointing jitter was typically <2'' in radius, only
a factor of 
worse than the IPS in optical hold. Several observations,
particularly those of bright stars, had no visible guide stars, however, and
the only way to guide was a combination of looking for light leaking from the
edge of the HUT aperture and guessing pointing corrections that would compensate
for the gyro drift rates.