Mars Ascent Vehicle

The Mars Ascent Vehicle, commonly shortened to the MAV, is the space vehicle used by Ares astronauts to evacuate the surface of Mars.

It contains a chemical plant that produces methane, oxygen and water.

Ares III
The Ares III MAV was located in Acidalia Planitia close to The Hab. It was used on Sol 6 by five of the six crew members when they had to evacuate early due to a dangerous dust storm encompassing the area. Astronaut Mark Watney was presumed dead on evacuation and the rest of the crew left without him. However, he survived but was injured by a piece of broken antenna.

Ares IV
The Ares IV MAV is located in Schiaparelli Crater and was placed there long before the date Ares IV mission was scheduled to take place. It may be used by the maretians to leave Mars

Venkat explains the specifications of the MAV to Annie