The primary UoSAT-2 spacecraft computer software

Following the launch and successful operation of the two UoSAT spacecraft, a mini operating system has been implemented on the primary on-board computers of each satellite. Known as the `Diary¿, it enables a range of spacecraft activities to be performed in a regular sequence, or at times defined by a real-time clock/calendar facility. This paper provides an insight into the philosophy of the system structure, and gives details pertaining to the design constraints imposed by the nature of the target processor. An outline description of the Main Tasks is given, together with examples of the various data formats utilized. The problems associated with sending and receiving data from spacecraft in low, polar Earth orbits are discussed, and methods used in overcoming these difficulties are detailed. Following on the development of the Diary system, originally for UoSAT-2, it was modified for use on UoSAT-1 thereby greatly enhancing the operational capability of that satellite in orbit. The paper identifies the modifications necessary for the Diary to run on the UoSAT-1 primary spacecraft computer.