QUESTION:
Why is the satellite dish so large on the MARS PATHFINDER?  (5 feet)

ANSWER from Guy Beutelschies on January 30, 1997:
The ground antenna we use to communicate with Mars Pathfinder is 34 
meters across.  It is that large because our spacecraft is so far away.  
It is over 4000 times as far as the Earth orbiting satellites that 
broadcast Television signals.

Having a ground antenna that large also allows us to have a small 
antenna (0.3 meters) on our spacecraft.