A radio relay station in orbit above the earth that receives, amplifies and redirects analog and digital signals contained within a carrier frequency. Based on their distance from the earth, there are three categories: GEO, LEO and MEO. Geostationary (GEO) satellites are in orbit 22,282 miles above the earth. Because they rotate with the earth, they appear motionless to an observer on the ground. The GEO downlink to earth can be localized into small areas or cover as much as a third of the globe's surface. Low-earth orbit (LEO) and medium-earth orbit (MEO) satellites are much closer to the ground, and they revolve around the planet. See GEO, LEO and MEO. Fixed and Mobile Satellite Services (FSS/MSS) Delivery from a communications satellite may be to stationary terminals such as rooftop dishes (FSS) or to mobile terminals in cars, planes and ships (MSS). See satellite bands, Teledesic, Iridium, DSS, FSS, DirecPC and bent pipe architecture.