Skylab's Apollo Telescope Mount (ATM) was this country's first full scale manned astronomical observatory in space. It was a predecessor to the currently proposed Spacelab experiment observational systems. The ATM experiment canister, which housed the eight principal solar telescopes, was three m long, over two m in diameter, and weighed approximately 11,200 kilograms. The system was designed to operate within a pointing accuracy of ± 2.5 arc-sec and within a stability accuracy of ± 2.5 arc-sec over a 15-minute observation period. Review of photographic data indicated that the Experiment Pointing Control System (EPCS), which controlled the ATM experiment canister, performed with a stability of better than 1.0 arc seconds, exceeding its design requirement by a factor of 2.5. The EPCS was a part of the Skylab Attitude and Pointing Control System (APCS) which utilized momentum exchange devices and cold gas thrusters for overall vehicle control. The EPCS operated in a nested configuration within the vehicle control system. It was designed to isolate the ATM experiments from vehicle disturbances in two axes, up/down and left/right. Roll positioning control was also available. A fine sun sensor (FSS) provided position information while rate information was obtained from canister mounted rate gyros. Torque motors on each of the dynamic axes responded to controller signals to position the experiment canister.