NASA Investigating Possibility Mars Lander’s Engines Shut Off

Engines controlling the final descent of NASA’s Mars Polar Lander might have shut off prematurely, sending the $165-million probe crashing to the surface, according to a new theory that is being investigated.

Engineers have found a design flaw that could have caused the spacecraft’s engines to switch off while the probe was still more than 100 feet above the surface. A fall from that altitude would have destroyed the spindly probe.

The glitch is one of several possibilities under investigation in the loss of Polar Lander, engineers said this week. The craft was last heard from Dec. 3, just before it was to begin its descent to the surface for a 90-day mission to study Mars’ climate history.

“The problem has been identified with the design,” said Sam Thurman, the lander’s flight operations manager at NASA’s Jet Propulsion Laboratory. “That’s one of several possible causes of loss of mission that have been identified during the investigation.”

Two review boards are examining the various failure possibilities and implications for future Mars missions. But because no data were returned during the lander’s descent, the reason for the failure may never be conclusively known.

Other possibilities are that the spacecraft landed on the steep side of a canyon and toppled over, that its complicated descent system thrust unevenly or its radios broke down.

The latest theory to emerge suggests that jarring during descent, possibly from release of the craft’s back shell, might have triggered an early shutoff of the dozen, tea-cup-size descent engines, causing an uncontrolled drop to the surface.

The thrusters were designed to turn off after one of the probe’s three legs made contact with the ground, which should have triggered a switch. But shutoff could have occurred as high as 130 feet off the ground, according to the theory.