MSTI-3 Spacecraft Attitude Control Software Development using Automatic Code Generation

Current budgetary trends in space development programs are stressing the "cheaper, faster, better" philosophy. Reduction in cost is attained most effectively by reducing program schedule. Advances in Computer Aided Software Engineering (CASE) products now make vastly reduced spacecraft software development schedules possible. The Miniature Seeker Technology Integration (MSTI) spacecraft program, developed by Phillips Laboratory-Edwards Air Force Base, utilizes CASE tools to design, develop, and test on-board flight software within a one year schedule. Such a short schedule is achieved principally by automatic Ada code generation. This greatly reduces laborious hand-coding and debugging, and allows the controls engineers to move quickly from algorithms to an executable program, running on the spacecraft processor, ready for testing. The MSTI satellites are the first spacecraft to employ automatically generated code in the on-board flight software. The MSTI-3 flight software incorporates 10 Attitude Control System (ACS) modes (3-axis stabilized), fault-tolerant features, and commanding via stored and up-linked commands. Automatic code generation of all the attitude control software, and much of the sensor processing greatly reduces the turn around time for design, development, integration, and test. This paper will present the methodology for MSTI3 software design, development, and test, and describe the ACS algorithms which include: Attitude Acquisition (Inertial Capture, Sun Acquisition, Stellar Search and Recognition), Attitude Determination, and Attitude Control.