Optical Inter-Satellite Link Demonstration on CubeSats - Update on the CubeISL-IOD Mission

Kurzfassung

Free-space optical communication has become a mature technology to extend and replace classical radio channels for data transmission from satellites to the Earth. The advantages of high data throughputs, resilience against electromagnetic disturbances and its robustness against jamming spoofing and eavesdropping makes laser communication attractive for governmental, defense authorities and commercial users. To enable global connectivity and interoperability beyond the line of sight, inter-satellite links are required and therefore terminals with high data rates are necessary to avoid communication bottlenecks. Size weight and power limitations on spacecraft demand highly efficient and miniaturized payloads, especially for use cases on smallest satellites. The German Aerospace Center (DLR) developed laser communication terminals especially designed for CubeSats. The next step is to ransfer this technology from direct-to-Earth into the inter-satellite domain. Thus, DLR developed the CubeISL terminal to establish an optical connection between two identical terminals to exchange information with a data rate of 100 Mbps over distances of up to 1,500 km. The standardized formfactor of just 1U allows easy and simple integration into standard CubeSat busses and the separation of the receiver and transmitter signal by wavelength allows building up constellations containing multiple satellites. The capabilities of the CubeISL terminals will be demonstrated in a relevant, operational scenario on two 6U CubeSats built by the Spanish company Alén Space. The mission is led by Responsive Space Cluster Competence Center and the satellites will be operated by the German Space Operations Center, both as parts of DLR. This paper gives an update on the latest state of the project. It depicts the status of the terminal development as the key component of the in orbit demonstration mission. The two carrier platforms are described briefly and their concept is explained. Laser communication is highly dependent on the pointing performance and a stable orbit control. In addition, the capabilities of the optical connection will be demonstrated and evaluated in different distances. All this leads to strict requirements for the satellites, especially for the attitude and orbit control system. The concept to achieve this precision and accuracy is briefly discussed. Furthermore, the paper describes the mission architecture and the operations concept. Different communication standards used in the terminal, the satellite and the ground segment require an aligned coordination of the protocols and standards. Alén Space will take care of the satellites during the launch and early orbit phase and hand over the satellite to DLR afterwards. This transition and the following operations concept of the laser experiments are briefly discussed as well.