4 Final Report - Emits - ESA

4 Final
Report
Reception of the instrument data by mobile terminals is also possible, but affects the necessary onboard
transmit power. For example, assuming a 3m diameter mobile reception antenna, the on-board
RF power will increase to approx. 50W requiring the use of TWTAs for the amplification instead of
SSPAs.
4.5.5 Telemetry and Telecommand
General
The S-Band Subsystem provides all classical Tracking, Telemetry and Command (TT&C) services.
Ranging and range rate services are implemented according to the ESA ranging standard. Power Flux
density requirements are respected during all normal operational phases (except launch).
TM
TC - Data
& Clock
TC - Data
& Clock
TM
Transmitter 1
(nominal)
Ranging
&
Coherency
Receiver 1
(nominal)
Transponder 1
Transponder 2
Receiver 2
(hot redundant)
Ranging
&
Coherency
Transmitter 2
(cold
redundant)
Figure 4.5-7: S-Band Subsystem
Diplexer
Diplexer
3 dB -
Combiner
Nadir
Antenna
Zenith
Antenna
The S-band communications subsystem consists of two transmitters, two receivers, a 3dB Combiner,
two antennas, and RF harnessing. The nominal RF transfer from and to ground will be achieved using
a combined receive/transmit quadrifilar helix (QFH) antenna mounted on the nadir side. An identical
QFH antenna on the zenith side is used to establish ground contact for off-nominal attitude conditions.
While both receivers are running in permanent hot redundancy, one of the two transmitters will be
switched on via the Spacecraft Computer Unit (SCU) when required to perform ranging or to downlink
the housekeeping telemetry data to the ground station and will, usually, also be switched on prior to
Page 4-56 Doc. No: GOC-ASG-RP-002
Issue: 2
Astrium GmbH Date: 13.05.2009
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