GSC Sentinel-2 PDGS OCD - Emits - ESA

ESA UNCLASSIFIED – For Official Use
GSC Sentinel-2 PDGS OCD
Issue 1 Revision 2 (draft) - 25.07.2010
GMES-GSEG-EOPG-TN-09-0008
page 126 of 350
For this, the capabilities offered by the satellite design outlined in 3.5.4 and further
detailed in [AD-03] and [RD-41] regarding NRT prioritisation or RT downlink will be
used as described in section 4.5.4.2.2; .
It is assumed for this final stage that the timeliness partitioning will be compatible with
the respective capabilities and grants allocated accordingly at the previous
configuration steps.
○ A scene security constraint [TBC] to ensure that the last MSI scene downlinked is
effectively entirely transmitted before LOS (~3.5 seconds TX duration per scene).
○ The requirements provided through the HLOP for the parallel accommodation of LGS
direct-downlinks introduced in section 4.2.7 according to the operation scenario
detailed in 4.5.4.3.
○ The accommodation of ancillary-data downlinks at the term of each downlink at every
CGS or LGS as further explained separately in section 4.5.4.2.3.
○ The accommodation of HKTM data downlinks at selected CGSs according to the
operation scenario detailed separately in section 4.5.5.
The mission plan elaborated by the PDGS will comprehensively optimise the detailed
downlink scenario based on the above considerations.
Considering the maximum size of the on-board MSI store of 2360 Gbits corresponding to
about 5 times the storage requirement of an average orbit, this limit will not jeopardize the
nominal scenario even considering acquisitions campaigns complementing the nominal
acquisition plan (cf. 4.5.4.1.1). In case of a degraded contingency downlink scenario required
to operate with less than 4 stations, the data acquisition plan will be reduced accordingly to fit
within the 2360Gbits packet store autonomy. A safety check in this respect will be
implemented to invalidate plans neglecting this constraint.
4.5.4.2.1.4 CGS Scheduling
As driven by the detailed mission plan settled with the FOS, the CGS schedule will be
generated to trigger the on-ground data reception activities (cf. section 4.5.4.2.4). This
scheduling will be performed periodically and will include:
o A reception schedule to enable the satellite acquisition from the station antenna;
o A front-end processing schedule to enable front-end processing activities.
This decoupled scheduling between data reception and front-end processing activities will
be used to selectively manage the acquisitions between overlapping ground station contacts
Whilst the reception schedule will ensure satellite tracking from satellite entry into the station
visibility mask, the front-end processing schedule will selectively map to the data playback
activities assigned to the station in the downlink plan.
4.5.4.2.2 MSI Packet-Store Management
Following the logic described in the previous paragraph, the detailed downlink planning of
MSI data will require the accurate management of the on-board MSI packet-store to gradually
playback the data acquired and buffered on-board according to the timeliness requirements
set for each image segment.
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