Edoardo Benzi

Alphasat-Sentinel-1A optical inter-satellite links: run-up for the European data relay satellite system

Laser Communication Links in Orbit have become routine for Alphasat TDP1 GEO data relay and Sentinel-1A LEO satellite. Since November 2014, an extensive campaign has demonstrated stable and bit-error free links over distances of up to 45.000km with 1.1W optical transmit power and data rates of up to 1.8Gbps. Link acquisition is achieved reliably within less than 55s. Links with low grazing altitude investigate the impact of atmosphere to link performance. The optical links between Sentinel-1A and Alphasat are in collaboration of ESA, DLR, and TESAT Spacecom. Alphasat TDP1 is the precursor for European Data Relay Satellite System EDRS [1].

Optical Inter-Satellite Communication: the Alphasat and Sentinel-1A in-orbit experience

Since late 2013, the 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. TDP1 was developed by TESAT Spacecom for DLR, with the objective to demonstrate and characterise a LEO to GEO optical communications link. TDP1 is able to receive observation data from a lower orbit (LEO) spacecraft thanks to its Laser Communication Terminal, and route the data to ground via a Ka-band RF link performed by its own Ka-band System. In the absence of a counter-terminal aloft, the activities concentrated initially on characterising and optimising the terminal performances using the ESA Optical Ground Station in Tenerife. With the launch in April 2014 of Sentinel-1A in its sun-synchronous orbit, an in-flight companion for the ASA terminal was made available. Operated by ESA on behalf of the European Commission as part of the Copernicus program, S1A performs its earth observation mission thanks to a Synthetic Aperture Radar, and carries on board an Optical Communication Payload, based on another TESAT Laser Communication Terminal. As a proof of concept for the upcoming European Data Relay Satellites system (EDRS), an Optical Inter-Satellite Link demonstration campaign started in September 2014. Using an incremental approach that led to the first data transmission from Sentinel 1A in November 2014, the campaign was completed in December 2014, with results well beyond expectation in terms of link performances. A subsequent “Experimentation Phase” aiming at the characterisation of the paired terminal performances over its operational envelope has been going on since the beginning of 2015. In the meanwhile, the launch of Sentinel 2A provided the second LEO counter-terminal for TDP1. Beyond the technological complexity of the laser communication terminal and the outstanding results obtained, the exercise presented some remarkable operational challenges. Planning, scheduling and executing a link implies coordination of the activities of the two missions engineering and operations systems and teams, with the necessary involvement of the laser terminal provider team expertise. In addition to providing the ultimate demonstration of the technology underlying the EDRS, the Alphasat and Sentinel 1A experiences have thus provided 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 segment.

Optical LEO-GEO Data Relay: The In-Orbit Experience

Laser-based data transmission in orbit is available for commercial application, opening a new chapter for satellite communications. Optical LEO-GEO data relay pave the Space Data Highway for Earth Observation Spacecrafts in low Earth Orbit by offering fast access to large quantity of data. The Sentinel-1A / Alphasat TDP1 optical data relay is operational since November 2014. More than 100 successful links have been performed since, both of nominal as well as experimental character, demonstrating reliable and stable link service with adequate system margins for the implementation of the European Data Relay Satellite System EDRS. This paper presents key performances and hands-on experience from in-orbit operations of the optical data relay.

Benefits of using Advanced Planning and Scheduling Technology: The Alphasat TDP Operations case

In July 2013, Alphasat, Europes largest and most sophisticated telecommunications satellite, was launched from Kourou, French Guiana. In addition to its main commercial payload, four Technology Demonstration Payloads (TDPs) fly on-board. These payloads are provided by different research institutes, which are in charge of defining in-orbit demonstration tests of these new technologies. Therefore, to optimize this opportunity, coordination of possibly conflicting payload operations is required. This is one of the roles of the TDP ESA Coordination Office (TECO). To cope with the coordination requirement, an advanced planning and scheduling software system, the TECO System, has been designed to support the Alphasat operations and, in particular, to manage and coordinate the payload requests. The system was developed on top of the APSI planning framework, re-using some of its general modeling and solving functionality, and integrating ad-hoc evolutions to match the problem requirements. The TECO system was designed to be completely automated (i.e., it should run without any human intervention in the nominal case), considering the need to autonomously provide the end users (i.e., TDP Operation Centres) with the necessary information to understand the planning process, the analysis of the input requests, and the final operation plans. In this paper we present the planning and scheduling system and discuss how its functionality influenced the definition of the Alphasat TDP Operations concept. In addition, as the system is operational since October 2013, we also provide an initial assessment of operations so far.