QUESTION:
Communication with Pathfinder has ceased. What happens to the Mars rover
Sojourner? Does it stop and wait or move according to some program?  If so,
what is it doing?

ANSWER from David Mittman on November 7, 1997:
The rover's on-board contingency sequence is invoked when the rover goes
without communication with the lander for a specific time period. After that
time, the rover attempts to drive back to the vicinity of the lander in
order to reestablish communications. (The assumption on the part of the
rover is that it hasn't heard from the lander because it has strayed outside
communications range.) Eventually the rover will encounter a "virtual
obstacle" representing the lander, and attempt to stay away from that
obstacle. The net effect is that the rover will then drive around the
lander, while attempting to satisfy the conflicting goals of approaching the
lander's ground zero and avoiding the area within three meters of the
lander.

David Mittman
Jet Propulsion Laboratory