The draft ECSS SpaceWire Backplane standard

The SpaceWire standards are maintained and issued formally as ECSS documents (e.g. ECSS-E-ST-50-12C) and this means that equipment designed by different agencies is interoperable, which has significant benefits.SpaceWire is mainly used between instrument units, however to facilitate a high level of integration of onboard systems it is proposed that an ECSS SpaceWire Backplane standard should be created and adopted, the backplane offering power, signal and impedance-matched connectivity for high-speed serial links such as SpaceWire and SpaceFibre. The SpaceWire Backplane standard will assist in the aim of creating a common onboard infrastructure to be used across many different mission applications by encouraging design reusability at the sub-unit (PCB plug-in module) level. A key advantage of a SpaceWire Backplane is the scalability of the design. A draft SpaceWire Backplane ECSS standard has been created by TAS-UK as part of an ESA contract. It is based around the Smiths Connectors Nexus modular connector which can be populated with a variety of different contact inserts for power, signal and high-speed data and thus can be tailored to a particular application. The standard will specify the physical dimensions, connectors and electrical interfaces of the unit backplane and plug-in module. Units and plug-in modules will then be interoperable, so for example a module produced by one vendor will correctly fit into a unit from another vendor and interface correctly with the backplane electrical signals. It permits both non-redundant and redundant units to be built and does not dictate the backplane SpaceWire network architecture. Recommendations are made to assist in the creation of reliable fault-tolerant systems. It is intended that this ECSS document takes advantage of specifications already existing, namely other ECSS and also ANSI/VITA VPX standards. The principal VITA standards are referenced include VPX (VITA 46), OpenVPX (VITA 65) and a new draft standard SpaceVPX (VITA 78). It is anticipated that there will be a harmonisation activity in future between the SpaceVPX and this ECSS document before the formal ECSS standard release. This paper is a walk-through of the ECSS Backplane standard, it describes the thought processes and rationale behind it and the anticipated advantages of adopting it.