The thing to keep in mind," says Benton Clark, chief scientist for flight systems at Lockheed Martin Astronautics, "is that [on any planetary spacecraft] there are around a thousand or so separate individual things that have to be verified somehow--by test, by inspection, by analysis. The pilot on an airplane does 10, 20, 30 things; we have to do a thousand." By the evening of Saturday, Dec. 4, the day after NASA's latest Mars missions were due to land at the planet's south pole, it was clear that either some of those things had gone wrong, or else that the universe had played a cruel trick on the scientists trying to understand it.
Over the course of the day since it had reached the planet, the Mars Polar Lander--built for NASA by Lockheed Martin--had maintained a stony silence despite ground control's attempts to coax it into speech. So had its two companion microprobes, Scott and Amundsen, named for the Antarctic explorers. The silence from the microprobes was especially ominous; in all likelihood, they were lost for good. After the loss of the Mars Climate Orbiter two months ago, the problems raise new questions about NASA's approach to the Red Planet.
The day of the landing started in an upbeat mood. After fine-tuning their course one last time, the spacecraft's navigators had the probes on track "a gnat's eyelash" from the desired landing area near the planet's southern ice cap. "The whole team is ecstatic," said Sam Thurman, the flight-operations manager for the mission at the Jet Propulsion Laboratory (JPL) in Pasadena, California, which runs NASA's Mars missions. At this point, the lander and the two microspacecraft were all attached to the cruise stage, a support system that took care of them during the long trip from Earth.
Only 10 minutes before the journey's end, after communication with Earth had been severed, was the cruise stage to release the three packages bound for the surface. After that the microprobes were to plummet to the surface, hitting it at 400 mph and driving their sensors a few feet into the soil to look for ice. The Polar Lander was to make a more sedate approach to the planet, with a parachute and then a suite of engines slowing its descent before it touched down.
The simplest explanation why no radio signals were received is that, for some reason, the cruise stage was not jettisoned. If so, the whole squadron was either torn apart by the atmosphere or smashed by the unyielding ground. But the silence could easily have a more complicated and less catastrophic set of explanations. Even a relatively minor software glitch could have persuaded the Polar Lander to put itself into a "safe mode" after landing--which would have meant turning off its systems for more than a day before rebooting itself and trying to re-establish contact. Alternatively, something could have gone wrong with the communications system. The antenna supposed to track Earth could have jammed, or been unable to work out which way to point. The silence of Scott and Amundsen was more worrying. Over Friday night Mars Global Surveyor made numerous attempts to get the microprobes' mobile-phone-like radios to talk as it passed over their landing site. Because they are powered by batteries, the microprobes have to be found within three days if any data is to be retrieved.
If all three spacecraft remain silent, NASA, JPL and Lockheed Martin--which also made the ill-fated Mars Climate Orbiter--will all face searching criticism. JPL's Mars program exemplifies NASA's commitment to "faster, better, cheaper" missions. But as Clark Chapman, an asteroid specialist, recently pointed out in an address to the American Astronautical Society's Division of Planetary Sciences, "faster, better, cheaper" has a patchy record. In 1997 the Earth-observing satellite Lewis failed just after launch. An orbital telescope called the Wide-field Infrared Explorer lost its vital coolant earlier this year. One of NASA's own asteroid missions, Deep Space One, failed to point its camera the right way, while another, the Near Earth Asteroid Rendezvous, will turn up more than a year late for its date with the asteroid Eros because of a problem with firing its engine.
Clearly, space missions are dangerous propositions. There's a lot to get right, and even if everything checks out perfectly in advance, things can still go wrong. If the south polar region of Mars has hidden rocks in its apparently smooth soil, for instance, they could have sealed the fate of the microprobes and tipped over the Polar Lander. Going to a place no eye has ever seen and no radar measured is always going to leave scientists open to unpleasant surprises. That's the nature of exploration. But it's no excuse for poor judgment and an inability to prepare properly. Perhaps, in retrospect, it was not such a good idea to name one of the microprobes after Robert Scott. A heroic failure is still a failure.
SPACE