The space objects now orbiting Earth range from satellites weighting several tons to pieces of spent rocket bodies weighing only 10 pounds. About seven percent of the space objects are operational satellites, the rest are debris. Below is a brief description of each type of sensor. Phased-array radars can maintain tracks on multiple satellites simultaneously and scan large areas of space in a fraction of a second. These radar's have no moving mechanical parts to limit the speed of the radar scan - the radar energy is steered electronically.
Conventional radars use moveable tracking antennas and fixed detection and tracking antennas.
The detection antenna transmits radar energy into space in the shape of a large fan. When a satellite intersects the fan the energy is reflected back to the antenna, triggering the tracking antenna. The tracking antenna, then, locks its narrow beam of energy on the target and follows it in order to establish orbital data. The Electro-optical sensors consist of telescopes linked to video cameras and computers. The video cameras feed their space pictures into a nearby computer which drives a display scope.