Standard Payload Computer for the International Space Station

This paper describes the development and application of a Standard Payload Computer (SPL-C) which is being applied by the majority of ESA payloads accommodated on the International Space Station (ISS). The strategy of adopting of a standard computer leads to a radical rethink in the payload data handling procurement process. Traditionally, this has been based on a proprietary development with repeating costs for qualification: spares, expertise and maintenance for each new payload. Implementations have also tended to be unique with very little opportunity for reuse or utilisation of previous developments. While this may to some extent have been justified for short duration one-off missions, the availability of a standard, long term space infrastructure calls for a quite different approach. To support a large number of concurrent payloads, the ISS implementation relies heavily on standardisation, and this is particularly true in the area of payloads. Physical accommodation, data interfaces, protocols, component quality, operational requirements and maintenance including spares provisioning must ail conform to a common set of standards. The data handling system and associated computer used by each payload must also comply with these common requirements, and thus it makes little sense to instigate multiple developments for the same task. The opportunity exists to provide a single computer suitable for all payloads, but with only a one-off development and qualification cost. If this is combined with the benefits of multiple procurement, centralised spares and maintenance, there is potential for great savings to be made by all those concerned in the payload development process. In response to the above drivers, the SPLC is based on the following concepts: A one-off development and qualification process A modular computer, configurable according to the payload developer's needs from a list of space-qualified items An 'open system' which may be added to by payload developers Core software providing a suite of common communications services including a verified protocol implementation required to communicate with the ISS A standardized ground support equipment and accompanying software development environment The use of commercial hardware and software standards and products.