Notice that it is a Schmidt-Cassagrain antenna, a parabolic main reflector with a hyperbolic sub-reflector. It searched in a revolving motion like conventional AC&W radar until it detected a target (satellite or missile), then the antenna assembly stopped and went into acquisition mode. The motor behind the sub-reflector started it spinning (with an intentional off-center wobble), so that an `error signal` could be generated. It then tracked the target by locking onto the strongest part of the error signal. Not only could it track in azimuth, but it could track in elevation, too, turning itself all the way over if necessary. After it was done tracking a target, it resumed its normal search mode. Its limitations were than it was a mechanical assembly that was prone to breakdown, and it could track only one object at a time. Eventually all the AN/FSS-7 sensors were rendered obsolete by the PAVE PAWS phased-array radar systems at Otis ANGB, MA, and Beale AFB, CA. [Two other PAVE PAWS radars were built at Robins AFB, GA, and Eldorado AFS, TX, but both of these have since been shut down. The radar from Eldorado has been relocated to the 13th MWS, Clear AFS, AK (BMEWS).]