QUESTION:
How many pictures does the camera take in an observation period?

ANSWER from Tom Comeau on APril 14th,1996:
Remember that we don't have to have fixed observation periods -- we don't have
to wait for night, since it's always night in space.  We do have to wait for
things we want to examine to be in a visible spot, and we do bundle things
up in convenient chunks to work with.

For example, we can't point the telescope close to the Sun, the Moon, or the
bright Earth, as that could damage the optics and instruments.  And for most
of an orbit half of the sky is behind the Earth, because we're in such a low
orbit.

Also, the amount of time we need to take an image varies a lot.  For bright
things, like planets, we may take very short exposures.  One of the Comet
HYAKUTAKE-1 exposures was a one second exposure.

For faint things, like distant galaxies, we may leave the shutter open a
very long time, or even take many fairly long exposures of the same target
>and add the images together.  One set of Hubble Deep Field exposures had
many 800 second exposures superimposed on one another to get an effective
exposure time of several days!

The observations for the telescope are scheduled in what are called Science
Mission Specifications that usually last a week.

Observers are usually awarded a specific number of orbits for their programs,
and an orbit is about 95 minutes.  The whole orbit isn't generally usable, as
we have to do some "housekeeping" to operate the telescope, and the target
may be behind the Earth for part of the orbit.  The scheduling team works
with the observer to plan their orbits, including selecting good exposure
times.

The SMS that included the  "Live From Hubble" Neptune and Pluto pictures
had observations for 35 different programs.  The Pluto pictures included
two Faint Object Camera pictures taken in a 54 minute period; six Neptune
WFCP2 images in a 55 minute period, and another six Neptune WFPC2 images
in a 55 minute period.  Each of those periods was most of an HST orbit.

So the number of pictures we take with each camera depends on two major
variables:  The amount of time, usually in number of orbits, that an observer
has been assigned, and the length of each exposure.  It varies a lot, but
the>Pluto and Neptune pictures are pretty typical for planetary astronomy:
You
can get anything from a couple to a half dozen pictures per orbit.