Page 291 - Concise Encyclopedia of Robotics

SATELLITE DATA TRANSMISSION S
Satellite data transmission is a form of microwave data transmission, but
the repeaters are in space, not on the ground. Signals are sent up to the
satellite, received, and retransmitted on another frequency at the same
time. The ground-to-satellite data are called the uplink; the satellite-to-
ground data are the downlink. Satellite data transmission can be used in
the remote control of robots over great distances, and in outer space.
Many satellites are in geostationary orbits, at fixed spots 36,000 km
above Earth’s equator. When such a satellite is used, the total path length
is always at least twice this. The smallest possible delay is therefore ap-
proximately ⁄4 s. High-speed, two-way data communication is impossible
1
with a path delay that long, as is realistic telepresence. However, teleopera-
tion (simple remote control) of robots is possible.
The illustration shows a system that uses two geostationary satellites

Satellite X Satellite Y
Signal path

North geographic
Signal Signal
pole
path path

Station X Station Y
Satellite data transmission

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