SpaceWire network and communication technology in the MMX system Mission and Applications, Short Paper

Mitsubishi Electric Corporation (MELCO) has applied SpaceWire for internal component links and mission instruments interface with high-speed links so far. This time MELCO had a chance to apply it for the MMX (Martian Moons eXploration) system network. This paper describes the network topology, protocols, communication technologies and lessons learned in this system. The MMX mission is a project planned launch in the mid-2020s, to explore the two moons of Mars. Data handling (DH) subsystem including two components: SMU (Satellite Management Unit) and MDP (Mission Data Processor) is responsible for the master and relay of the network. Thirty SpaceWire nodes and six SpaceWire Routers (in RTG4 and GR740) are in the MMX system. We apply SpaceWire as internal SMU/MDP links, interface between SMU and MDP, SMU/MDP and mission instruments, SMU and Retrievable Data Recorder (RDR). These communication data is used for not only DH but also Guidance Navigation and Control (GNC) subsystem. Although each node has variety of data size and collection frequency, software in SMU/MDP controls transaction with 64Hz timing slots to achieve acquiring all HK telemetries and observation data. The MMX system consists of three modules (Propulsion Module, Exploration Module and Return Module) which is separated in operation. We apply SpaceWire at the interface between SMU and MDP, SMU and RDR, which interface will be separated. Therefore, we have designed the circuits in SMU to protect from external noise because these will be exposed outer space due to the separation. RDR is the mission component and there is severe limitation of the number of harnesses between SMU and RDR interface. For this reason, we have developed Strobe-less communication technology, which is useful for the systems that have limitation on the number of harnesses.