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

Abstract

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.

Impact of spectral noise shape and correlations of laser beam jitter on acquiring optical links in space

“…The number of optical links established between satellites in space has rapidly increased over the past two decades, from first communication experiments between the Artemis and SPOT4 satellites via the the SILEX system [1] in 2001, to current routine high-performance links between the Alphasat satellite on geostationary-orbit (GEO) and the Sentinel-1A/1B satellites on low-earth orbit (LEO) [2]. The future European Data Relay System comprises a network of satellites equipped with optical terminals that provide global coverage for fast data transmission between network nodes in order to support high resolution imaging for crisis management and security applications, offering secure point-to-point communication over large distances [3].…”

Analysis of performance and robustness against jitter of various search methods for acquiring optical links in space

“…Following this step, one transceiver may lock its local laser onto the signal received from the remote transceiver by a phase-lock loop, which is referred to as "frequency acquisition". Such a twostep process is applied for the Laser Communication Terminals (LCTs) [10] or for gravitational wave detectors in space [11]. Contrary to this approach, for the GRACE FO mission 5 degrees of freedom must be varied up to the point where all of them match simultaneously and the link is established [12,13].…”

“…The LCTs used in the EDRS use the simplest possible acquisition sensor consisting of a quadrant photo-diode During the acquisition process one of the terminals, terminal 1, initiates a 2-dimensional search scan in angular space while the other terminal, terminal 2, detects any "hit" on its four quadrant sensor system and re-orients itself in accordance to the detected hits density distribution [2,10]. In the next step, the roles are swapped and terminal 2 scans while terminal 1 re-orients itself.…”

Laser Technology in Photonic Applications for Space

“…Later, other missions, such as the Alphasat TDP1 GEO mission launched in 2013, used the same LTC equipment. The test consisted in communicating between the Alphasat and the Sentinel-1 satellite (launched in 2014) and the transfer of 1.8 Gbits of data per second across a distance of 45,000 kilometers was demonstrated [104,105]. In that case, the downlink data transfer was performed with a Ka-band RF from the GEO satellite in order to increase the duration of the transmission link thanks to the geostationary orbit.…”