Washington

The Mars Polar Lander that disappeared without a trace last December probably crashed into the planet due to a software error, according to a report to be released this week. A committee chaired by John Casani, former chief engineer at the Jet Propulsion Laboratory, which managed the doomed spacecraft, identified the programming error after examining several possible accident causes.

The lander's legs had micro-switches that were to have signalled onboard engines to shut down when the legs made contact with the surface. But the switches sensed a jolt when the landing legs unfolded during the descent through the Martian atmosphere, and faulty software failed to tell the difference between the jolt and a real landing. As a result, the engines shut off prematurely, and the lander fell the rest of the way to the surface with no retro-rockets to soften the blow.

A second panel of outside experts, chaired by former aerospace executive Thomas Young, identified more generic problems, as have other reports issued in recent weeks, which have criticized NASA for poor management and underfunding of missions ranging from the space shuttle to the Mars Climate Orbiter that also failed last autumn.

Tony Spear, a former manager of the successful Mars Pathfinder project who reviewed NASA's ‘better, faster, cheaper’ missions for its administrator Daniel Goldin, said at a recent NASA Advisory Council meeting that “we should slow the rate of missions until we understand how to do them.”

NASA and JPL are already planning to overhaul the Mars programme as a result of the reports, according to sources. The changes are likely to include more intense supervision of the programme at NASA headquarters, less emphasis on sample return as the main focus of the Mars effort, and using small missions to conduct a reconnaissance of the Martian surface before sending large landers.