Software and the Challenge of Flight Control

A mythology has arisen about the Shuttle software with claims being made about it being “perfect software” and “bug-free” or having “zero-defects,” 1,2 all of which are untrue. But the overblown claims should not take away from the remarkable achievement by those at NASA and its major contractors (Rockwell, IBM, Rocketdyne, Lockheed Martin, and Draper Labs) and smaller companies such as Intermetrics (later Ares), who put their hearts into a feat that required overcoming what were tremendous technical challenges at that time. They did it using discipline, professionalism, and top-flight management and engineering skills and practices. Many lessons can be learned that are still applicable to the task of engineering complex software systems today, both in aerospace and in other fields where software is used to implement critical functions. Much has already been written about the detailed software design. This essay will instead take a historical focus and highlight the challenges and how they were successfully overcome as the Shuttle development and operations progressed. The ultimate goal is to identify lessons that can be learned and used on projects today. The lessons and conclusions gleaned are necessarily influenced by the experience of the author; others might draw additional or different conclusions from the same historical events. To appreciate the achievements, it is necessary first to understand the state of software engineering at the time and the previous attempts to use software and computers in spaceflight.