By the middle of 1961, RCA had a contract with NASA to build, a 4000 mile high, medium-orbit, active communications satellite called RELAY, AT&T was working on its own medium-orbit satellite called TELSTAR, and Hughes Aircraft Company had an exclusive contract to build a 24-hour orbit, 20,000 mile high satellite, called SYNCOM. By 1964, two TELSTARs, two RELAYs, and two SYNCOMs had operated successfully in space. The transponder technology used by AT&T in the TELSTAR I satellite is current technology in use today