A Consolidated ACS Flight Software Development Approach for the Earth Observing-1 Spacecraft

The Earth Observing 1 (EO-1) mission is part of NASA’s New Millennium Program (NMP). The EO-1 Attitude Control System (ACS) flight software was based on the Tropical Rainfall Measuring Mission (TRMM) flight software, both of which were developed by the Hammers Company, Inc. Lessons learned during TRMM ACS software development led to a consolidated software development approach for the EO-1 ACS. The approach started with a standalone system that incorporated the “first-cut” flight software into the spacecraft simulation, allowing closed loop simulations to run on a desktop computer. Consequently, more algorithm and coding errors were detected earlier in the development process. The consolidated system was connected directly to a ground support equipment computer in order to develop test procedures, ground system databases, and display pages. For flight software testing, the system’s spacecraft simulation module was used as a spacecraft simulator, and the flight software was removed and loaded onto the test or flight hardware. This type of consolidated development approach decreased dependency on hardware deliveries and allowed for a reduced level of software testing to continue through hardware down time. This approach helped meet the challenge of EO-1’s shorter schedule and lower cost as compared to TRMM.