In-orbit demonstration of the world's smallest laser communication terminal - OSIRIS4CubeSat / CubeLCT

Kurzfassung

Classical RF-communication is physically limited in bandwidth and the number of usable channels is constantly decreasing due to the increasing number of satellites in space. Channel crosstalk and sensitivity for interferences lead to a well-conceived frequency selection to avoid disturbances or outages. Hence, registration of applicable channels at International Telecommunication Union (ITU) takes several months nowadays. Free Space Optical (FSO) communication provides solutions for high data-rate transmission, without interferences, electromagnetic disturbances or unwanted crosstalk between communication channels. Thus, it is free of registration and time-consuming administrative processes can be avoided. In 2016 German Aerospace Center (DLR) started the development of OSIRIS4CubeSat (O4C), together with their industrialization partner Tesat Spacecom GmbH. The outcome of this cooperation is the worlds smallest Laser Communication Terminal (LCT), especially designed for CubeSats. With its low Size, Weight and Power (SWaP), its high data-rates and the robustness against electromagnetic effects, O4C transforms satellite communication and enables several new capabilities on small spacecrafts. The handover to industry is already finished and Tesat offers the terminal under the name CubeLCT to commercial customers. The first version of O4C is flying in the PIXL-1 mission on a 3U CubeSat with the name CubeL. This paper gives an overview of the technology of the space and ground segments and the demonstrator mission. Therefore, it describes the O4C payload which uses the Pointing, Acquisition and Tracking (PAT) system, by its integrated Fine Pointing Assembly (FPA), to establish a connection with an Optical Ground Station (OGS). Furthermore, it describes CubeL with respect to the requirements for the LCT and the relevant subsystems for the mission. CubeL is equipped with an RGB-camera, so that real pictures as operational data are transmitted over O4C to the Earth. This use case allows to prove the capabilities of O4C in a quasi-operational scenario. Beside the space segment, the paper briefly describes the operation of the Optical Ground Station Oberpfaffenhofen Next Generation (OGSOPNG), the required beacon system and the Electrical Ground Support Equipment (EGSE), which are necessary to complete the optical data transmission path. The paper shows the results of the In-Orbit Verification (IOV) of the optical downlink, from the first flashes over successful tracking to the final picture transmission. Examples of telemetry and received data are depicted and discussed. These data demonstrate the performance of O4C during the mission, in comparison to the previously calculated link budget. Furthermore, the paper outlines the high dependencies on precise and reliable Attitude Determination and Control Systems (ADCS). O4C establishes the transformation of modern satellite communication in a miniaturized and efficient form factor. The capabilities proven in the PIXL-1 mission and the modular approach of the terminal allow multiple new future applications. The paper concludes with an outlook to representative examples like Optical Inter-Satellite Links (OISL) and Quantum Key Distribution (QKD).