GSC Sentinel-2 PDGS OCD - Emits - ESA

GSC Sentinel-2 PDGS OCD
Issue 1 Revision 2 (draft) - 25.07.2010
GMES-GSEG-EOPG-TN-09-0008
page 122 of 350
In practice, such acquisitions will be handled such as to avoid any impact on the overall
baseline mission objectives (e.g. timeliness conflicts), possibly using the margin left within the
available downlink budget.
Nevertheless, the mission-planning capabilities will provision for the possibility of acquisition
campaigns to take precedence over the nominal acquisition scenario if needed.
To provide for additional trade-off, the MSI acquisition scenarios will take advantage of
Sentinel-2 constellation capabilities and embed load balancing between the spacecraft
acquisition plans (e.g. alternate acquisition campaigns on Sentinel-2A and Sentinel-2B
spacecrafts).
As detailed in section 4.5.4.10, additional and possibly interfering acquisitions will be
performed recurrently for Cal/Val activities. Although generally taking precedence over the
nominal plan, the impact of Cal/Val requirements on the mission plan will be very limited.
To satisfy the MSI constraint described in section 4.3.8.3, the MSI acquisition plan will ensure
that the instrument nominally enters standby mode when the spacecraft reaches eclipse after
the descending measurement pass. At the end of the eclipse period, the MSI will be switched
back into idle mode to reach thermal stability 300 seconds before the start of image
acquisitions at the next pass. Exceptions to this rule will however be permitted to allow for
seldom acquisitions to be performed during night time (e.g. for dark-signal acquisitions or
specific acquisition campaigns). In this case and according to the planned night-time
observations, the instrument commanding to standby (resp. from standby) will be delayed
(resp. anticipated) to satisfy at best the constraint when better qualified.
The detailed MSI acquisitions scenario implemented during phase-E2 will be implemented
from HLOP input along the principles defined above. During Phase-E1 of any spacecraft, the
PDGS Commissioning Plan (CP) will supersede the HLOP for the operations relevant to that
spacecraft.
4.5.4.1.2 Ancillary Data Acquisitions
The processing of MSI data on-ground requires time-correlated satellite ancillary data. To this
end, satellite ancillary data will be nominally acquired on-board without interruption and stored
into the dedicated Ancillary-data memory store. This memory will be managed as a circular
buffer such that newly acquired data systematically and autonomously replaces the oldest
one within the total allocated buffer size.
It is assumed this recording operation is not requiring any specific triggering at PDGS
mission-planning [Assumption-16].
4.5.4.2 Core Mission Data-Recovery On-Ground
The operation scenario for Sentinel-2 satellite downlinks aims for:
○ The systematic recovery on-ground of all satellite generated data with an optimised
apportioning of RT, NRT and nominal timeliness characteristics driven through the
HLOP;
○ A very systematic and steady process to the maximum feasible extent.
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