Analysis and Impact of the End-to-End Communication Chain on a DLR Real Time On-Orbit Servicing Mission Project

Kurzfassung

The German Aerospace Center, DLR, is researching and developing technol-ogies to enable future robotic On-orbit Servicing (OOS) missions. Current studies are being undertaken by the RICADOS (Rendezvous, Inspection, Cap-turing and Detumbling by Orbital Servicing) project. RICADOS traces its heritage to the proposed Deutsche Orbitale Servicing (DEOS) mission. The project employs a holistic approach to developing the key technologies and operational procedures for OOS missions in a collaborative effort between multiple DLR Institutes. It encompasses several disciplines: camera and visu-al technologies for inspection, guidance, navigation and control (GNC) pur-poses, and autonomous real-time telerobotic operations. Furthermore, a key aspect of the project is the integration of operations into the operational Ger-man Space Operation Center (GSOC) mission control infrastructure. This en-ables conducting end-to-end tests from the satellite and robotic control con-soles, across the simulated ground and space communication chain, to the (simulated) satellite bus, employing the tools and procedures that are used by real missions. Additionally, hardware-in-the-loop operations are conducted using the European Proximity Operations Simulator (EPOS 2.0) and On-Orbit Servicing Simulator (OOS-Sim) facilities at the DLR Space Operations and Astronaut Training Institute and Robotics- and Mechatronics Institute, re-spectively, in Oberpfaffenhofen (Munich, Germany). This allows real-time mission operations focusing on testing and verification of complex rendez-vous, inspection, and capturing manoeuvres. Carrying out real-time telerobotic activities with visual and haptic feed-back during these operations impose constraints to the communication chain and protocols regarding packet loss, round-trip delay, and jitter. One ap-proach is to deal with these restrictions by implementing dedicated communi-cation links for conducting robotic operations, which would not allow simul-taneous TM/TC operations. RICADOS manages to conduct both standard spacecraft TM/TC and robotic operations by multiplexing the independent robotic payload and CCSDS/ECSS compliant spacecraft bus TM/TC data streams into a single physical communication link. This offers the ability to independently and simultaneously process the robotic payload and spacecraft bus control data. The ground segment and communications link are simulated by the Communication System (COSY). COSY handles conversion and ho-mologation of the space protocols, multiplexing of spacecraft and robotic data streams, and simulation of the communication link via a wide-area-network ground and space link. The multiplexing and demultiplexing of the data stream is realized using a FPGA (Field Programmable Gate Array) hardware device as part of the communication system. Furthermore, it enables main-taining the strict timing requirements for real-time operations as the FPGA uses a fixed clock. This paper reports on the testing and evaluation of the COSY communica-tion chain, following four years of successful implementation and operation. The testing and analysis aimed to characterize the delay and jitter across the COSY system and its sub-systems, with a view to determining compliance with the RICADOS project's latency and jitter requirements of 100 ms and 2.5 ms, respectively. The results of the testing and analysis indicated that cross-device latency and jitter meet the requirements in relevant cases, setting the stage for further optimization and development of the COSY system.