NASA's ambitious plans for a series of Mars Surveyor landers and orbiters, leading to a sample return mission in 2005, depend upon a successful touchdown of the Mars Pathfinder at Ares Vallis on 4 July.

The landing site is at the outflow at the bottom of a valley in which it is thought a river flowed early in Martian geological history.

The Pathfinder, launched in December 1996, will be protected by a heatshield as it penetrates the Martian atmosphere at 7.6km/s, and a parachute will be deployed at 10km altitude.

The heatshield and parachute will be deployed and the Pathfinder, encased in inflated airbags, will hit the surface at 32m/s. The craft will bounce along the terrain for as long as 2min.

If it achieves the first successful Mars landing since the September 1976 visit by the US Viking 2 laboratory, the Pathfinder will deploy a six-wheeled "intelligent" robotic roving vehicle. The vehicle, called the Sojourner, is the size of a microwave oven, measuring 630mm long, 480mm wide and 280mm high.

The Pathfinder and Sojourner are expected to be operated for 30 days and seven days, respectively, and will return stereo images which will be accessible "live" on the Internet.

Source: Flight International