Getting Real With The Real-time Clock

摘要

In the 1990s, I was the lead servo-system engineer for the world's largest radio telescope (Reference 1). Our team was responsible for real-time motion control of 30 45m-diameter giant antennas that composed the radio telescope. Astronomers sitting at a central console focused the antenna position on the target-the radio star under observation. Because the rotation of the earth causes apparent drift in the position of the target, the antenna had to track the target by moving accordingly. The servo system was supposed to "servo track" this motionrnunder the supervisory control of the central computer. By 1993, a few of the prototype antenna systems were undergoing proving trials, which uncovered many painful surprises. The chief astronomer reported that the antenna was drifting off the target by minutes-and that was just one of our problems.