Operations Design, Test and In-Flight Experience of the Sentinels Optical Communications Payload (OCP)

The Copernicus Sentinel-1 and Sentinel-2 Earth Observation missions are the first in history to use a LEO to GEO optical communications (i.e. laser) link to routinely downlink stored science data to the ground. The start of routine operations with EDRS A has represented a major milestone for both of the Sentinels missions and is the culmination of more than two years of intense and sustained operational validation activities by the FCTs. This chapter provides a summary of validation and test activities that have been performed during the Sentinel-1 and 2 satellite commissioning, then with Alphasat and finally with EDRS A, to achieve the current operational state. This chapter also describes how the OCPs are accommodated on the Sentinel-1 and Sentinel-2 satellites and the on-board services each OCP requires. The basic principles of how the OCPs on the LEO and GEO spacecraft establish a communications link with each other are also described. Each Sentinel spacecraft executes between 9 and 12 OCP communications links per day. The timing of these links is scheduled by the Sentinels Payload Data Ground Segment (PDGS) with the EDRS A service provider. The PDGS provides the link timing information to the Sentinels Flight Operations Segment (FOS) at ESOC where the Sentinels Mission Planning System has a dedicated function that is used to determine the necessary telecommand parameters for uplink and execution. We will describe the end-to-end link planning concept and process, highlighting the data exchange interfaces and will explain what telecommand parameters the OCP requires to execute a link and how they are calculated. The start of routine OCP operations with EDRS A has also introduced an extra level of operational complexity into the daily operations working practice of both Sentinel-1 and 2. Next, we will describe the impact of the routine OCP operations on the following operational areas; mission planning operations; orbit maintenance operations; collision avoidance operations; anomaly recovery operations; general operations working practice. The chapter will also focus on the operation lessons learned. We will also summarize the benefits to each mission of optical communications, showing how the use of optical communications, together with X-band ground station downlinks, has been used to maximize the data output of the missions. Finally, we will describe how the OCPs will be used in the future on both Sentinel-1 and Sentinel-2.