There are several unique features of telemetry system design for spacecraft. One of these is the approach to the fact that for any given satellite in LEO, because it is traveling so quickly, it may only be in contact with a particular station for ten to twenty minutes. This would require hundreds of ground stations to stay in constant communication, which is not at all practical. One solution to this is onboard data storage. Data storage can accumulate data slowly throughout the orbit and dump it quickly when over a ground station. In deep space missions, the recorder is often used the opposite way, to capture high-rate data and play it back slowly over data-rate-limited links. Another solution is data relay satellites. NASA has satellites in GEO called TDRS, Tracking and Data Relay Satellites, which relay commands and telemetry from LEO satellites. Prior to TDRS, astronauts could communicate with the Earth for only about 15% of the orbit, using 14 NASA ground stations around the world. With TDRS, coverage of low-altitude satellites is global, from a single ground station at White Sands, New Mexico.