Mars Exploration Rover landing. Artwork of the parachute, rocket and air bag system that will be used to safely land the unmanned Mars Exploration Rovers. An orbiting spacecraft will release each rover, which enters the atmosphere protected by a heat shield. A parachute slows the descent, and a rocket is fired just before impact. Inflated air bags are needed to protect the lander from impact speeds of up to 100 kilometres per hour. The lander will bounce about 12 times and roll about 1 kilometre. The two NASA rovers will study Martian rocks and look for water. They will land in January 2004.