Communications With Earth

How the rovers can communicate through Mars-orbiting spacecraft

Not only can the rovers send messages directly to the DSN stations, but they can uplink information to other spacecraft orbiting Mars, utilizing the 2001 Mars Odyssey and Mars Global Surveyor orbiters as messengers who can pass along news to Earth for the rovers. The orbiters can also send messages to the rovers. The benefits of using the orbiting spacecraft are that the orbiters are closer to the rovers than the DSN antennas on Earth and the orbiters have Earth in their field of view for much longer time periods than the rovers on the ground.

Because the orbiters are only 250 miles (400 kilometers) above the surface of Mars, the rovers don´t have to "yell" as loudly (or use as much energy to send a message) to the orbiters as they do to the antennas on Earth. The distance from Mars to Earth (and from the rovers to the DSN antennas) during the primary surface missions varies from 110 to 200 million miles (170 to 320 million kilometers).