NASA has all but given up on the Mars Polar Lander, which descended into the Martian atmosphere on Friday but hasn't been heard from since. Space scientists say they may never know what doomed the $165 million spacecraft.
The failure adds another mission to a dismal record of missions to the Red Planet. Since 1960, the United States, the USSR, and then Russia have launched 29 missions toward Mars, only eight of which could be called real successes. The snakebit Russians are batting zero for 16. Until this year, however, U.S. scientists seemed to have largely dodged the gremlin, having scored 8 successes out of 11 attempts. But then in September, confusion over English and metric units doomed Mars Climate Orbiter (ScienceNOW, 10 November). And with the Mars Polar Lander (MPL) missing, the United States can count just two successes in the last five tries.
Most discouraging, perhaps, is the likelihood that no one may ever know what sealed MPL's fate or whether some undiscovered flaw in current designs makes upcoming Mars missions anything more than gremlin bait. One of two things might have happened to MPL. It could have suffered some onboard problem after it broke off radio communication with Earth, as intended, 12 minutes before its planned landing. A complex sequence of mechanical operations was scheduled to follow--separation from a cruise ring that had supported the spacecraft, a fiery entry behind its heat shield, parachute deployment, jettisoning of the heat shield, radar locking onto the surface, separation from the parachute, and a rocket-powered deceleration to a gentle touchdown on the surface.
With no word from the lander, engineers don't know how any of that went. MPL had no way of communicating during its entry, descent, and landing, unlike the successful 1997 Mars Pathfinder. That mission, notes project scientist Matthew Golombek of the Jet Propulsion Laboratory (JPL) in Pasadena, California, was testing a new airbag-cushioned landing method, so documenting spacecraft performance every step of the way was mandatory. For MPL, spacecraft designers, who were following the lead of the two Viking spacecraft that landed successfully on Mars in 1976, economized by leaving out the somewhat complex and expensive equipment needed for continuous communications.
In the only other possible disaster scenario, MPL, after touching down as intended, might have fallen prey to the martian terrain. As in all previous landings on Mars, no one had a preview of exactly what MPL had to deal with. According to Richard Zurek, MPL project scientist at JPL, images of the landing zone made by the orbiting Mars Global Surveyor showed relatively smooth terrain well within MPL's capabilities. But each picture element in most of those images encompasses 4 meters, so plenty of lethal hazards--car-size potholes or meter-high ledges, for example--could be lurking in otherwise gentle terrain. "We can't capture [lander-scale hazards] with the images we have," says Zurek. "That's a risk you take when you go to Mars. We're going to places on Mars we haven't been before. You can't guarantee success."