Model Rocket Engine Software System (MRECS) is a system of control software that was originally intended for use in controlling rocket engines but is also applicable to almost any real-time, closed- loop process-control system — for example, the feedback control system of a robot. MRECS affords the capabilities necessary for feedback control, actuation of valves and other devices by use of discrete and/or analog commands, processing of sensor readings, and generation of alarms by comparison of various quantities with limiting values. MRECS is capable of real-time multitasking and is amenable to distributed processing. It is designed, from the outset, to be highly maintainable and to be flexible in the sense that, in response to changing requirements, it can be quickly and reliably modified and tested.
In previous efforts to develop rocketengine- control software, there was an emphasis on minimizing the costs of development. However, the costs of maintenance and operations are significant parts of total life-cycle costs. In the development of MRECS, there has been less emphasis on limiting the cost of development and more emphasis on utilizing modularity and flexibility to reduce the costs of maintenance and operations.
MRECS takes advantage of the inherent support for modularity in the Ada programming language to implement real-time multitasking. Of all the enginecontrol programs in the experience of personnel at Marshall Space Flight Center, MRECS is the first to use real-time, preemptive priority-scheduled multitasking, the first to run on a commercial offthe- shelf (COTS) real-time operating system, and the first to use the standard Transmission Control Protocol/Internet Protocol (TCP/IP) for both command input and telemetry output. Through the use of Ada and COTS system software, MRECS has been made transportable to a variety of state-of-the-art computers and operating systems. In use, the worth of MRECS has been proven in that MRECS has been shown to be adaptable to different engine configurations and characteristics, to be amenable to rapid modification, and to perform engine- control functions reliably.
This work was done by Robert L. Stevens and Richard H. Beckham of Marshall Space Flight Center.