QUESTION:
If the Pathinder is solar powered and only runs in the day, where does it go
in the night, and about what time does it start working again?
 
ANSWER from David Mittman on June 27, 1997:
Both the Mars Pathfinder lander and the Sojourner rover rely on solar power
for most of their operations. However, both of them also have batteries. In
the case of the lander, the battery is rechargeable; Sojourner's battery is
not rechargeable as using rechargeable batteries wasn't necessary and would
have made the rover heavier and more expensive.

The lander's battery is used during the night to keep the computer operating
while we take temperature measurements and pictures of stars and Mars'
moons. During the day, the battery is recharged from solar power.

Sojourner's battery is used during the first night to conduct a 10-hour
measurement of the chemical makeup of a selected rock. The battery is also
used when Sojourner needs to drive over particularly harsh terrain.
Sojourner can drive as early as 10:00 AM Mars time without using its
batteries. The rover will usually drive until about 2:30 PM Mars time when
it will stop in place and wait for daybreak to continue driving.