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Alphasat, Sentinel-1A/B, Sentinel-2A/B, and EDRS Paving theWay for Systematic Optical Data Transfer for Earth Observation Missions

Since late 2013, Inmarsat operated Alphasat GEO communication satellite has been providing a reliable platform for the experimental activities of its 4 hosted Technical Demonstration Payloads (TDPs), procured and operated by ESA. Amongst them, TDP1 is capable to receive observation data from a lower orbit (LEO) spacecraft thanks to its Laser Communication Terminal (LCT), and route the data to ground via a Ka band RF link. With the launch of Sentinel-1A in April 2014, of Sentinel-2A in June 2015, of Sentinel-1B in April 2016, and of Sentinel-2B in March 2017 in their sun-synchronous orbits, an increasing number of in-flight companions for the ASA terminal were made available. Part of the Copernicus program, the Sentinel satellites perform their earth observation missions thanks to a Synthetic Aperture Radar (S1A and S1B) and a Multi-Spectral Imager (S2A and S2B) respectively, and carry on board an Optical Communication Payload, based on the same TESAT LCT embarked on Alphasat. An Optical Inter-Satellite Link demonstration campaign in late 2014 with ASA and S1A using lead to the first data transmission from S1A in November 2014. The campaign was completed with results well beyond expectation in terms of link performances. Following the completion of the in-orbit commissioning of its Optical Communication Payload, S2A joined S1A in the following “Experimentation Phase”, aiming at the characterisation of the paired terminal performances over its operational envelope, that has been going on since the beginning of 2015. S1B and recently S2B have also been used as companion to Alphasat TDP1 terminal for their in orbit testing and calibration activities in the light of their commissioning into the now operational European Data Relay Satellite system. The Alphasat and Sentinels experience has provided the ultimate demonstration of the technology underlying the EDRS, and also made available an important opportunity to test the system operations in a realistic scenario and gain valuable experience to be put to fruition for the EDRS GS and operations, as well as for any future optical intersatellite communication system.