Data can be sent to Earth from a lander on Mars either by a direct-to-Earth communication or by relaying the data through a satellite orbiting the planet. The two Viking landers in the 1976-1982 period used both methods to communicate. The Mars Pathfinder in 1997 had only a direct-to-Earth capability, because when the spacecraft was designed it was understood that there would be no orbiter in place to relay the data.

An antenna large enough to communicate directly to Earth from Mars is included on the Mars Polar Lander. However, such an antenna would be much too large for the two Deep Space 2 Microprobes, thus these communicate only by relay through the Mars Global Surveyor Mars Relay antenna.

Mars Polar Lander data were mostly going to be sent to Earth by relaying through the Mars Climate Orbiter. This spacecraft was sent ahead of the lander so that it would be in position to support the lander mission in December 1999. However, Mars Climate Orbiter was lost as it arrived at Mars because it came too close to the planet during its attempt to enter orbit and either broke up or burned up in the atmosphere. Thus, the Mars Polar Lander now relies upon a combination of direct-to-Earth communication and data relay through the Mars Global Surveyor which has been in orbit since 1997.