QUESTION:
I would like to know about the procedures used to retreive
information from Mars Pathfinder.

ANSWER from David Mittman on November 22, 1996:
The computer onboard Mars Pathfinder is constantly collecting
information about the health of the spacecraft. This information is
packaged and transmitted by the spacecraft's antenna to Earth where 
it is received by one of the Deep Space Network antenna complexes. 
(As I type this, I'm monitoring the data that are coming from the 
spacecraft and being received by our Deep Space Communications 
Complex in Spain). If the package of data is complete (if parts of the 
package haven't been corrupted or ruined by "space static"), then our 
computers here at JPL decode the information and display it on our 
computer screens. The process isn't that much different than using a 
home computer modem to send email or transfer files.

At present, Mars Pathfinder is sending us data at a speed of 1,185 
bits per second. Compare that speed to the speed of most common 
computer modems: 28,800 or 14,400 bits per second. Why so slow? 
Well, the transmitter on Mars Pathfinder only puts out about 13 
Watts of power (the same as your average refrigerator light bulb), 
and that little bit of power has to travel 1,200,000 miles at last 
count (same as about 50 times around the Earth, or 200 times from 
Los Angeles to New York, round-trip).