Unified communication infrastructure for small satellites

Typical state of the art on-board communication infrastructure comprises two independent communication architectures. Command and control operations use a robust low data rate bus such as MIL-STD-1553B or CAN Bus. Payload data-handling systems rely on high data rate interconnection networks such as SpaceWire. This double scheme is not so useful for small satellites where control and data handling operations can be executed by the same processing units and mass and energy are very restricted. This paper presents SpaceWire-RT, a unified communication scheme based on the implementation of a Quality of service layer over SpaceWire networks, a space proven technology. SpaceWire-RT provides the reliability and timeliness required by command and control operations while keeping high data rates for the payload instruments. Reliability is provided using a retry mechanism and a redundancy scheme with alternative paths for packets to be routed over. Timeliness with soft guarantees is provided with packet segmentation and the use of multiple channels with different priorities. Hard guarantees and determinism are provided using time-slots and a Time Division Multiplexing technique that allows opportunistic utilization of unused reserved bandwidth. Besides, data stream applications can benefit from the end to end flow control function. The proposed solution uses currently available SpaceWire components, including radiation hardened units. It has been designed to be efficiently implemented in hardware and software and the network can be built using cables or backplanes. Besides, it reduces satellite development costs by using a well known easy-to-use space technology, enforcing reusability and isolating the user application from the control and data transport issues.