TT&C over S-Band with CubeL: Finding a Middle Way Between CSP, CCSDS and ECSS

Abstract

Since early 2021, the German Space Operations Center (GSOC) of DLR with Weilheim Ground Station operates its first COTS CubeSat: CubeL, also known as PIXL-1. Besides the main objective of validating a miniaturized space-to-ground optical communication terminal developed by DLR-IKN and Tesat-Spacecom, CubeL shall demonstrate the execution of Telemetry, Tracking & Command (TT&C) operations between a modern CubeSat and a classical multi-mission (MUM) environment with the help of a S-band communication link. CubeL, on the one side, relies like many other CubeSats on the CubeSat Space Protocol (CSP), a well-established delivery protocol whose layering corresponds to the TCP/IP model. The advantages of CSP are its simplified structure, modularity, easy deployment, and free availability under the LGPL license. GSOC and Weilheim Ground Station (WHM), on the other side, have a long history in the operation of all types of space missions, manned or unmanned - near earth or deep space. MUM operations can only exist with the help of highly standardized communications. This is the reason why the core mission operations systems at GSOC and the ground station equipment rely on standards and recommendations like CCSDS 132.0-B-2 (TM Space Data Link Protocol, linked to ISO 22645:2016), CCSDS 133.0-B-1 (Space Packet Protocol, linked to ISO 22646:2005) and ECSS E-ST-70-41C (telemetry and telecommand packet utilization). This approach allows GSOC to support a large number of space missions and increases reliability while simplifying the integration of other stations to existing ground station networks. In this paper, we present CubeL, the involved S-band communication systems and the employed protocols. We detail the plan to integrate CubeL into GSOC mission operations, followed by the description of the journey towards operational TT&C using the GSOC S-band link. We conclude with some lessons learnt and suggest improvements for future integrations of CubeSat missions into multi-mission operations centers.