On-Board Software (OBSW)

The software has been developed according to the standard defined by the European Cooperation for Space Systems (ECSS). The standard defines a development process, according to the criticality of the system. ECSS defines four levels of criticality categories, A, B, C, D, where A is life threatening in case of a failure, B is mission threatening, C results in major degradation of the mission in case of failure. Category D is for ground software. Higher category implies more stringent process requirements.

The programming languages applied were C and Ada. For C, a safe subset was defined, and static analysis executed to ensure the rules were adhered to.
For Ada, specific coding rules were enforced by the compiler and accompanying tools.

Terma also participates in ESA research and study programs on on-board software (OBSW). Of special interest was the On-Board Software Reference Architecture study, which aimed at defining a satellite software architecture made out of a layer common to all missions (the Execution Platform), and a mission specific layer on top of the execution platform.

The ASIM mission main scientific objective is to study the correlation between Transient Luminous Events (TLEs) and Terrestrial Gamma-ray Flashes (TGFs) which occur in the upper atmosphere above thunderstorms. This is achieved by the two instruments, one optical instrument for observing TLEs (MMIA) and one X and Gamma-ray instrument for observing TGFs (MXGS). The two instruments implement advanced triggering algorithms for the identification of these event, and also cross-trigger each other to capture both optical and gamma ray data for all events which are potential candidates of TLE/TGFs.

Terma A/S is the prime contractor, with the Technical University of Denmark as the leading scientific advisory board.

Terma developed the instrument software for both instruments. The software is implemented in Ada, and executes on a Leon3 processor, based on an Ada runtime system. The instrument software shares some common functionality, while the specific data handling is of course different due to the nature of the instruments.

The software developed was of category C.

Read the ASIM case study.