4 Final Report - Emits - ESA

4 Final
Report
4.6.2.8 Ground Stations for Geo-Oculus
For the preliminary architecture of the Geo-Oculus ground segment it is foreseen to establish two
TT&C stations to provide redundancy for the TT&C functionality.
TT&C Ground Stations
The TT&C Stations are responsible for exchanging telecommands and telemetry with the satellite and
to provide ranging functionality. For the envisaged orbit determination based on the spread spectrum
ranging method, at least two S-Band stations are required; to achieve optimum performance three S-
Band Ground stations should be foreseen. It is recommended to use dedicated S-Band GEO ground
stations for the TT&C functionality providing permanent contact with the satellite.
Using the S-Band for TM/TC and ranging makes the system compatible to the LEOP G/S network.
During LEOP, commissioning and verification phase the LEOP G/S network can provide backup and
failsafe capabilities for the operational system within the initial verification phase. Additionally using a
lower frequency band like the S-Band in combination with a big G/S antenna size increases also the
ranging accuracy of the station.
The location of the primary S-Band TT&C ground station can principally be selected at free choice.
The only constraint is that the S-Band G/S needs a direct communication link to the operations
facilities (being ESOC in Darmstadt as a baseline), which allows a seamless exchange of the TM/TC
data between ESOC and the G/S. At present stage, the Agency's ESTRACK facilities located at
Maspalomas (Spain) is considered as primary ground station. The secondary ground station is
assumed to be located in Redu, Belgium. The monitoring and control of the S-Band ground stations
can be achieved remotely from ESOC by the staff already in place.
TT&C Standards and Interfaces
For compatibility reason to the ESOC/ GSOC G/S network, it is also recommended to follow the
CCSDS standard for the TM/TC data packets and to provide SLE (Space Link Extension) interfaces.
PDT Ground Stations
As a baseline for the Payload Data Ground Segment the main data reception facility shall be equipped
with a dedicated ground station to provide permanent contact with the satellite. As has already been
mentioned before, it is recommended as far as feasible that the receiving station is collocated with the
Payload Data Ground Segment in order to reduce the latency between data reception and processing.
What concerns the usage of a dedicated frequency band for payload data transmission, the ITU allows
for the data reception of GEO earth observation satellites to use the X-, DBS- or Ka-Band. At present
stage, the X-Band has been selected as baseline for the Geo Oculus PDT. The X-band is in the earth
observation domain the most commonly used frequency range for TM data transfer.
However, a GEO based S/C the utilisation of the X-band for payload data transmission may produce
interferences with the LEO systems. A LEO Ground Station located within this foot print can probably
cross this permanent GEO TM link through the tracking process of its LEO spacecraft. As a result of
the interference, it may be disturbed in its link and might loose its track. A small foot print of the GEO
S/C can reduce this risk, on the other hand, this increases the size of the TM transmit antenna on
board the S/C.
Page 4-86 Doc. No: GOC-ASG-RP-002
Issue: 2
Astrium GmbH Date: 13.05.2009