This portion of the Mars Science Laboratory spacecraft, called the cruise stage, will do its work during the flight between Earth and Mars after launch in the fall of 2011.

For example, it will provide propulsion for maneuvers to adjust the spacecraft's trajectory, and its solar panels will provide electricity for the spacecraft during the flight. The cruise stage will be jettisoned before the capsule containing the descent stage and rover enters the Martian atmosphere.

The Mars Science Laboratory spacecraft is being assembled and tested for launch in 2011.

This image was taken at NASA's Jet Propulsion Laboratory, Pasadena, Calif., which manages the Mars Science Laboratory Mission for NASA's Science Mission Directorate, Washington. JPL is a division of the California Institute of Technology.

Image credit: NASA/JPL-Caltech

This portion of NASA's Mars Science Laboratory, called the descent stage, does its main work during the final few minutes before touchdown on Mars.

The descent stage will provide rocket-powered deceleration for a phase of the arrival at Mars after the phases using the heat shield and parachute. When it nears the surface, the descent stage will lower the rover on a bridle the rest of the way to the ground.

The Mars Science Laboratory spacecraft is being assembled and tested for launch in 2011.

This image was taken at NASA's Jet Propulsion Laboratory, Pasadena, Calif., which manages the Mars Science Laboratory Mission for NASA's Science Mission Directorate, Washington. JPL is a division of the California Institute of Technology.

Image credit: NASA/JPL-Caltech

This image from August 2008 shows NASA's Mars Science Laboratory rover in the course of its assembly, before additions of its arm, mast, laboratory instruments and other equipment.

The six wheels are half a meter (20 inches) in diameter. The deck is 1.1 meter (3.6 feet) above the ground.

The Mars Science Laboratory spacecraft is being assembled and tested for launch in 2011.

This image was taken at NASA's Jet Propulsion Laboratory, Pasadena, Calif., which manages the Mars Science Laboratory Mission for NASA's Science Mission Directorate, Washington. JPL is a division of the California Institute of Technology.

Image credit: NASA/JPL-Caltech

The major components of NASA's Mars Science Laboratory spacecraft -- cruise stage atop the aeroshell, which has the descent stage and rover inside -- were connected together in October 2008 for several weeks of system testing, including simulation of launch vibrations and deep-space environmental conditions.

These components will be taken apart again, for further work on each of them, after the environmental testing. The Mars Science Laboratory spacecraft is being assembled and tested for launch in 2011.

This image was taken inside the Spacecraft Assembly Facility at NASA's Jet Propulsion Laboratory, Pasadena, Calif., which manages the Mars Science Laboratory Project for the NASA Science Mission Directorate, Washington. JPL is a division of the California Institute of Technology.

Image credit: NASA/JPL-Caltech

Full-scale models of three generations of NASA Mars rovers show the increase in size from the Sojourner rover of the Mars Pathfinder project that landed on Mars in 1997 (center), to the twin Mars Exploration Rovers Spirit and Opportunity that landed in 2004 (left), to the Mars Science Laboratory rover for a mission to land in 2012 (right).

The Mars Science Laboratory rover is about 9 feet wide, 10 feet long (not counting its robotic arm) and 7 feet tall.

The Mars Science Laboratory rover will have a mass of about 875 kilograms (1,929 pounds), compared with 174 kilograms (384 pounds) for each of the Mars Exploration Rovers and with 11 kilograms (24 pounds) for Sojourner. The main reason for the growth is to carry a larger payload of science instruments: about 83 kilograms (183 pounds) for the Mars Science Laboratory rover compared with 16 kilograms (35 pounds) for the Mars Exploration Rover and 1.4 kilograms (3 pounds) for Sojourner.

This image was taken in May 2008 at NASA's Jet Propulsion Laboratory, Pasadena, Calif., which has built the real Mars rovers and managed the rover missions for NASA's Science Mission Directorate, Washington. JPL is a division of the California Institute of Technology.

Image credit: NASA/JPL-Caltech