Sojourner had only a single UHF antenna for all control
and data communications. The Mars Exploration Rovers
carry three antennas, each designed for a specific purpose
and function. They are:
High-Gain Antenna
A High-Gain Antenna is pointed toward Earth to communicate
with the giant radio antennas of the Deep Space Network.
UHF Relay Antenna
A UHF Relay Antenna is designed to transmit signals
between the rover and an orbiting spacecraft, including
Mars Global Surveyor and 2001 Mars Odyssey. The orbiting
spacecraft can then be used as communications satellites
to relay information between the Mars Exploration Rover
and Earth.
Small UHF Antenna
This was the type of antenna
Sojourner used on Mars, and is the fall back communication
device for the Mars Exploration Rovers. A small UHF
Antenna is used to directly transmit information about
the rover's mechanical health and operating systems
back to Earth.
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