The
Mars Global Surveyor,
Mars Odyssey and
Mars Express orbiters carry the first generation of
UHF relay payloads. Building on this initial experience, NASA developed a next-generation relay payload, the Electra Proximity Link Payload, which flew for the first time on the 2005
Mars Reconnaissance Orbiter. A special feature is that it can actively adjust the data rate during a communication session – slower when the orbiter is near the horizon from the surface robot's perspective, faster when it is overhead. To build the relay network cost-effectively, NASA includes a relay communications payload on each of its science orbiters. Mars missions launched after 2005 make use of Electra UHF
transceiver to provide for any navigation, command, and data-return needs these missions may have. The arriving spacecraft can receive these signals and determine its distance and speed in relation to Mars. This communication allows much more precise navigation. When NASA's landers and rovers land safely on Mars, Electra can provide precise Doppler data which, when combined with
Mars Reconnaissance Orbiter position information, can accurately determine the location of the lander or rover on the surface of Mars. Electra can also provide
UHF coverage to Mars landers and rovers on the surface using its
nadir-pointed (pointed straight down at the surface) antenna. This coverage would be important to landed crafts on Mars that might not have sufficient radio power to communicate directly with Earth by themselves. ==Key features==