Instrumentation located on the Earth for monitoring, tracking, and communicating with satellites, space probes, and crewed spacecraft. Radars, communication antennas, and optical instruments are classified as ground instrumentation. They are deployed in networks and, to a lesser extent, in ranges. Ranges are relatively narrow chains of ground instruments used to follow the flights of missiles, sounding rockets, and spacecraft ascending to orbit. Some ranges are a few miles long; others, such as the U.S. Air Force's Eastern Test Range, stretch for thousands of miles. Networks, in contrast, are dispersed over wide geographical areas so that their instruments can follow satellites in orbit as the Earth rotates under them at 15° per hour, or space probes on their flights through deep space.