The first drive phase is defined as the period of time after landing during which engineers first conduct tests to ensure the rover is in a "safe state" and then move it for the first time beyond its original landing zone.

After entry, descent, and landing, the Mars Science Laboratory rover will not venture forth on its first drive until about the fifth day. The reason is that mission controllers on Earth need to make sure the surface directly beneath the rover's wheels does not present an immediate hazard. They also must complete deployment of the mast, the High Gain Antenna, the sampling system, test communications links, and make a few other checks before putting the proverbial "pedal to the metal." (Unlike prior rover missions, however, the Mars Science Laboratory rover will not have a lander from which it must egress. Instead, its mobility system--that is, its wheels and related parts--will be fully deployed prior to landing.)

One of the greatest concerns will be rover stability. Even though the rover can handle steep cliffs of up to 50 degrees and has a ground clearance of 60 centimeters (almost 2 feet), it's not possible to predict down to the last inch where the spacecraft will land. If the rover ends up, say, with one wheel on top of a rock and the others on a slope, engineers will want to know about it and make sure the rover maneuvers successfully to a safer position.

Upon landing, the Mars Science Laboratory rover will complete a series of automated computer sequences to make sure all systems are operating as expected and to check the immediate environment. For example, the rover will:

• Check martian temperatures to make sure they don't necessitate restrictions on operations;

• Test communications with Earth using the High-Gain Antenna;

• Test communications with Earth and orbiting spacecraft using the UHF antenna;

• Unfold the mast carrying the panoramic and navigation cameras and some of the science instruments;

• Take images as soon as possible after landing; and,

• Help mission controllers pinpoint the rover's precise location based on ground images, orbital images, and the length of time it takes for signals to travel between the rover and orbiting spacecraft.

After all of these tasks are complete, the rover will make its first drive from the landing zone onto uncharted martian terrain. The rover will test the many science instruments on board as exploration gets under way.