An extensible standards-based control system on a budget

The National Radio Astronomy Observatory (NRAO) in Green Bank was charged with replacing and enhancing the original control system on the NRAO 43-Meter (43m) telescope, for a minimum amount of labor, time and materials. The original 1960's vintage design required continuous operator presence for monitoring and control of the telescope. A fully automated, unattended operation was desired, along with better tracking performance at high speeds and reduced maintenance costs. We responded with a design based on proven industrial control technology, RTAI/Linux computers, and hardware and software adapted from the GBT and other NRAO telescopes. Commercial off-the-shelf software packages were also used in the system. We describe the overall design of the system and the decision process that led to the adoption of the various pieces of hardware and software, including the tradeoffs made between buying and building systems, and allocation of telescope functions between subsystems.