A lot of information has to pass between a spacecraft and supporting ground crews on any mission, including but not limited to telemetry, computer upload information, and voice communication. As early as 1962, NASA realized that the Apollo missions would demand a unique communications system. The Mercury and Gemini programs, both of which saw missions flying only in Earth orbit, used separate radio systems. Two-way voice communications, uplinked data, and downlinked telemetry were done using ultra high frequency (UHF) and very high frequency (VHF) systems while tracking was achieved with a C-band beacon on the spacecraft interrogated by ground-based radar. The system worked on simpler missions, but Apollo would be going much farther than Earth orbit, and with three men working in two spacecraft that would be operating simultaneously and sending down live television images, NASA needed a new way to uplink and downlink more data.