GSC Sentinel-2 PDGS OCD - Emits - ESA

4.3.10.4 X-Band Downlink Conflicts between Sentinel Missions
GSC Sentinel-2 PDGS OCD
Issue 1 Revision 2 (draft) - 25.07.2010
GMES-GSEG-EOPG-TN-09-0008
page 94 of 350
As it has been the case for the TMTC interface to the Sentinel spacecrafts in S-Band leading
to the pre-defined allocation described in section 4.3.7.1, potential conflicts among Sentinels
are also anticipated for the share of X-Band resources considering that:
○ The GSC aims for maximised common and interoperable usage of ground-segment
resources. This particularly applies to the Sentinels and to the common use of X-Band
ground-stations;
○ X-Band LEO-capable ground-stations are considered a scarce resource considering
the overall number of EO missions in flight, the required locations of ground-stations
and the investments they represent;
○ The data-rates introduced by the Sentinel missions and the dual spacecraft approach
for each mission require overall a very large number of X-Band station contacts to
recover the data on-ground;
○ The mitigation of the required X-Band downlink resources via the use of EDRS are at
this stage only considered as a potential future evolution.
In this respect, an on-going analysis is performed by ESA and concludes in a preliminary
analysis report [RD-29], that manageable but non-negligible X-Band access conflicts are to
be expected to support the increased volumes brought in by the Sentinels.
The X-Band downlink conflicts across the Sentinels missions can be classified as follows:
Signal interferences on ground when performing simultaneous X-Band downlinks: due
to the X-Band shared frequencies and different orbit cycles of the Sentinels,
simultaneous X-Band operations can produce seldom RF interferences;
Ground-stations resource conflict: in which the spacecrafts visibility over a groundstation
do not constrain simultaneous RF activities but the available allocated onground
resources (i.e. antennas availability);
The Sentinel-2 PDGS will hence account for these constraints when planning the mission
data downlinks to CGS and LGS such that:
Sentinel-2 X-Band transmission activities during specific periods can be precluded due
to other Sentinels (Sentinel-1 and/or Sentinel-3) conflicting X-Band activities having
priority during those periods;
Among all X-Band downlink opportunities offered by the CGS network for Sentinel-2,
some can be precluded or shortened by configuration due to prioritised access to the
CGS available antennas by other Sentinels;
It is assumed [Assumption-19] that based on the CGS and LGS networks, a conflict-free
coordination among Sentinels will result in a predefined definition of the above constraints
applicable to each Sentinel satellite in orbit.
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