QUESTION:
Is the data sent back from Mars Pathfinder digital or analog? If digital,
how fast is the transmission rate (i.e., baud rate)? How many channels of
data are there?

ANSWER from Leif Harcke:
We use digital modulation to send commands to and receive data from the Mars
Pathfinder spacecraft. Both the uplink and downlink use a residual carrier
binary phase shift keying (BPSK) modulation scheme.

Our command uplink data rate has several settings between 7.8125 bits per
second (bps) and 500 bps. Our telemetry downlink data rate has 20 settings
between 5 bps and 11060 bps. Currently, we are commanding the spacecraft at
250 bps and receiving data from the spacecraft at 1185 bps. As the
spacecraft moves further away from the Earth, we will lower our data rates
to compensate for the weaker signal. When the spacecraft arrives at Mars, we
will be commanding at 7.8125 bps and sending 40 bps on the downlink.

There is only one "channel" of data on both the uplink and the downlink. On
the downlink, we use packet time-division multiplexing to send both
engineering data (i.e., hardware status bits) and science data (i.e., camera
picture bits) in the same data stream.

--Leif Harcke, Telecommunications Systems Analyst