The nightmare continues

时间:2019-03-07 07:15:08166网络整理admin

By Charles Seife in Pasadena IF NASA’s latest Mars probe is declared a complete loss, as seemed inevitable as New Scientist went to press, the space agency is in serious trouble. Not only are its next two Martian landers nearly identical to the stricken craft, but there is also very little chance that engineers will ever discover what went wrong. Launched in January, the Mars Polar Lander ended its voyage on 3 December. If all had gone to plan, it would have landed near the planet’s south pole to analyse surface weather and soil. On its approach, it was supposed to turn away from the Earth, losing radio contact as it did so, then plunge through the atmosphere and deploy a parachute, eventually touching down with the help of its thrusters. It would then have unfurled its solar panels and beamed back a message signalling its arrival. That message never came. As New Scientist went to press, mission controllers at the Jet Propulsion Laboratory (JPL) in Pasadena were still attempting to contact the lander. But hope was fading fast, following the failure of several attempts using different radio antennas and different assumptions about what went wrong. Even attempts to detect radio signals from the landing zone using the orbiting Mars Global Surveyor yielded nothing. Two hitch-hiker probes, designed to detach from the craft and smash into the Martian soil, also remained silent. According to JPL spokesman David Seidel, the lander seemed to be in perfect health until radio contact was lost. “We clearly saw the turn begin,” he says. The probe was roughly on target, which should have placed it within a few kilometres of its intended landing zone. And that’s about all NASA engineers have to go on as they try to work out what happened next. Even the failure of the hitch-hiker probes doesn’t tell them much. The craft were supposed to separate early in the descent, and Sam Thurman, Mars Polar Lander’s flight operations manager, believes they almost certainly parted company as planned. He thinks the failure of the probes and that of the lander are likely to have been separate events. The loss of the Polar Lander is particularly worrying because NASA’s next missions to Mars, scheduled for launch in 2001 and 2003, use the same basic design. “We made them as identical as possible to save money,” explains Sylvia Miller, who helped design the craft. “In fact, we call it the workhorse lander.” It is already too late to make radical design changes to the 2001 project. In any case, there is little chance that re-examining the designs will uncover the flaw that claimed the lander, as this would simply be repeating work done following the loss of the Mars Climate Orbiter in September. Engineers corrected one problem: they found that the lander’s fuel lines were in danger of freezing solid and so switched on its heaters early (New Scientist, 20 November, p 15). But everything else looked fine. NASA officials are now wondering whether to redesign future probes to yield more information if they fail. One option is to give them small radio beacons to report the successful completion of each step in the landing sequence, but this would leave less room for important scientific equipment. “I don’t think that’s the correct direction,” says David Crisp, project scientist for NASA’s New Millennium space science programme. Other experts want NASA to change its “faster, better, cheaper” policy for space exploration. Following the loss of the $1 billion Mars Observer probe in 1993, the agency switched to missions costing around $125 million. “I wish we could have $300 million projects,” says John Logsdon, a space policy analyst at George Washington University in Washington DC. “We’re really trying to skip by and trust in technological luck.” Luck, unfortunately,