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The decision to use a programmable digital control system on the Space Shuttle engine was a new application of digital control in the early 1970's. The use of digital control was primarily based upon the need for a flexible control system capable of supporting the total engine mission on a large complex pump fed engine. The mission definition included all control phases from ground checkout through post shutdown propellant dumping.

The flexibility of the controller through reprogrammable software allowed the system to respond to the technical challenges and innovation required to develop both the engine and controller hardware. This same flexibility, however, placed a severe strain on the capability of the software development and verification organization. The overall development program required that the software facility accommodate significant growth in both the software requirements and the number of software packages delivered.

The above requirements became a serious challenge to the software development facility. This challenge was met by reorganization and evolution in the process of developing and verifying software. The resulting process consistently provided high quality