NASA's Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft is the latest link in the space agency's Martian communications network for keeping in touch with its surface rovers. Last week, the unmanned orbiter carried out a test using a special radio apparatus that allowed it to relay 550 megabits of data from the Curiosity rover to NASA’s Deep Space Network back on Earth.
Dropping a lander on the surface of Mars is an excellent way to gather data, but a ground-based transmitter is a terrible way to send it back to Earth. Landers, and especially rovers, have limited power, need to punch a signal through the Martian atmosphere, and for at least half the time aren't even pointing in the right direction.
NASA gets around these problems by using a tiny fleet of scientific orbiters circling the Red Planet to gather and boost the rovers’ signals before sending them on to Earth. Another advantage is that by using the orbiters and intermediaries, data can be sent back at a much greater rate than a direct link.
According to NASA, the key to this relay system is the Electra UHF radio. There’s one installed on MAVEN and similar ones on Curiosity and the Mars Reconnaissance Orbiter. These radios are designed to take into account the eccentric orbits of the spacecraft and compensate for them.
MAVEN, for example, has a very elongated orbit, which means that it’s often too far away for a more conventional link. NASA says that during the November 6 test, MAVEN was 680 to 2,300 miles (1,110 to 3,700 km) from Mars. During this time, Electra was able to adjust the data feed rate and signal strength accordingly as the orbiter passed over the rover.
According to NASA, MAVEN will be used as a backup relay during its primary science mission in case a fault develops with the other orbiters, and may act as a routine relay if its mission is extended.