SpaceWire for Operationally Responsive Space

The rapid integration, launch, and deployment of satellites in response to emerging needs have been a focus of various organizations. This concept has been termed "operationally responsive space" (ORS) by the United States Department of Defense (USDOD). One vision of ORS calls for the positioning in a depot of interchangeable satellite payloads and spacecraft buses with a common interface. Upon direction to deploy a particular mission, the appropriate payload would be selected and integrated with a bus, and the space vehicle would be launched. To support such a system, standardized hardware and software interfaces are needed between the payload and bus. For the development of ORS Bus Standards, the SpaceWire standard (ECSS-E-50-12A) has been specified as part of such a payload-bus interface for high rate data. Data interfaces can be modeled in a number of ways, such as with the OSI layer model. SpaceWire offers the appeal of standardization of physical, data, and network layers. The TacSat-4 satellite, part of the USDOD TacSat experiment series, is intended as a combination of a prototype Standardized Bus for small satellite national security missions and an example payload. This implementation includes an instance of the SpaceWire interface called out in the ORS payload developer\´s guide. For the bus and payload SpaceWire interfaces, existing SpaceWire logic designs were used, notably the gate array core developed by NASA GSFC. This was intended as a demonstration for ORS that use of existing and freely available intellectual property can streamline design, enhance reliability, and empower instrument and payload vendors.