STS-99 - SRTM Hardware--the Antenna
The Outboard Antenna Structure
The outboard antenna structure is connected to the end of the mast. It contains a
C-band and an X-band antenna, two global positioning system antennas, light
emitting diode targets, and a corner-cube reflector. The two outboard antennas can
only receive radar signals. Transmitting of radar signals will be done only by the
main antenna.
The C-band and X-band antennas on the outboard antenna structure receive radar
signals reflected from the ground. The signals are passed down cables to the
Shuttle for recording along with the signals from the main antennas.
Global Positioning System antennas will be used to gather accurate information on
the position of the Space Shuttle. Meanwhile, light emitting diode (LED) targets will
be used by a target tracker on the Attitude and Orbit Determination Avionics
(AODA), mounted on the main antenna, to measure the position of the outboard
antenna relative to the main antenna. A corner-cube reflector will be used by the
electronic distance measurement unit on AODA to measure the length of the mast
to within three millimeters (1/8 inch).
Source: NASA