QUESTION:
If the Mars Global Surveyor was knocked off course, would it be able to get 
back on course or not?

ANSWER from Charles Whetsel on May 12, 1997:
It depends on how far off it got knocked.  We are periodically making
small corrections to the trajectory as we go, but if something really big
knocked us really far off, it would be hard to recover.  The good news is
that space is a very big place and it is very hard to run into something
out there.  It would be almost impossible to hit MGS with a guided
projectile even if you tried very hard.  To hit it by accident with a
randomly orbiting asteroid or other body big enough to knock it off course
would take a miracle.