"VIRTUAL Payload INTEGRATION with SPaceWire"
Steve Parkes1, Stuart Mills1, Philippe Armbruster2, Raffaele Vitulli2
1University of Dundee
2European Space Agency, ESTEC
SpaceWire is a standard on-board, data-handling network that has been designed with reuse in mind . A standard network means that the instrument and data-handling sub-systems can be readily integrated at the physical and data-link levels. Making sure that the various sub-systems work together correctly is another matter. Spacecraft are often built by consortia with partners spread across several countries. Development teams are separated geographically and to some extent by culture and language. During spacecraft design, emphasis is on using documentation to help ensure the correct operation of the system. Detailed interface specifications are written for each subsystem and agreed between prime contractor and subcontractor. Misunderstandings or misinterpretations of specification lead to contract change notes and often to increased costs. Once the sub-systems have been developed, integration and testing requires the movement of the various units to a common location. This is usually done late in the development programme. Any fault or error in specification or design found at this late stage is expensive causing delays in the integration and test programme and may delay the launch of the spacecraft. Risk to the project is increased by the integration of the components late in the project schedule.
Virtual Payload Integration is a means of interconnecting onboard data-handling sub-systems early on in the development life cycle without bringing them to a centralized integration and test facility. Connection is provided by the Internet. Early interconnection reduces risk due to misunderstanding or misinterpretation of equipment specifications, resulting in a more manageable project.
This paper starts by introducing the concept of Virtual Payload Integration. It then describes the SpaceWire Internet Tunnel device developed by University of Dundee for ESA. This device is able to tunnel SpaceWire information through the internet, including SpaceWire packets, time-codes and error conditions. It allows a SpaceWire network to be constructed and functionally tested with nodes in different countries. Although the speed of SpaceWire cannot be met by the existing internet functional testing is possible, allowing many potential bugs to be eliminated prior to final physical system integration. The SpaceWire Internet Tunnel has been tested operating with SpaceWire sub-systems in ESTEC, Holland and University of Dundee, Scotland. More extensive testing is planned for later in 2006.
S.M. Parkes et al, ECSS-E-50-12A, “SpaceWire, Links, Nodes, Routers and Networks", Issue 1, European Cooperation for Space Data Standardization, January 2003.
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