Even though Japan’s problem-plagued Hayabusa spacecraft is now on its return trip to Earth, it might never complete the journey. A catastrophic failure of its last remaining reaction wheel, which helps point the craft, might prevent it from reaching the Earth to drop a capsule into the atmosphere, mission members say.
Hayabusa was meant to collect samples from the asteroid Itokawa by firing pellets into the surface of the 535-metre-long rock and scooping up the resulting debris. But data from two landings in November 2005 suggest the pellets never fired because the craft’s onboard computer sent conflicting signals to its collection instruments.
Still, mission officials hoped to bring the spacecraft back to Earth in case some asteroid dust had slipped into its collection chamber by chance. If it completes the trip, it is expected to drop a capsule in the Australian outback in June 2010.
But Hayabusa’s project manager, Jun’ichiro Kawaguchi, told New Scientist that if any other systems break down, it could be fatal to the mission. He is particularly concerned about the spacecraft’s last remaining reaction wheel. “We are eager to make it return with our best efforts, but the situation is not optimistic,” he says.
Mission managers are now pointing Hayabusa using jets of xenon gas from the craft’s ion propulsion system. The relatively weak thrusters, which use electric fields to accelerate a beam of xenon ions, were originally designed only to propel the craft forwards on its 2-billion-kilometre round trip to Itokawa.
Without the ability to aim the spacecraft, mission engineers could not maintain communication with Hayabusa or keep it on the right trajectory to return to Earth. The team lost contact once before, in late 2005, and regained it only three months later. A glitch this time would probably be permanent.
Despite these worries, mission planners could still pull off a safe landing, according to Hayabusa team member Don Yeomans of NASA’s Jet Propulsion Laboratory in Pasadena, California, US. “I wouldn’t bet against them – they’re doing pretty well,” he says.
Indeed, the team from the Japanese Aerospace Exploration Agency has managed to keep Hayabusa flying despite a long list of near-catastrophic failures, including the leaks of critical fuel and a temporary loss of contact with the spacecraft that caused its return to Earth to be delayed by three years.
“Yeah, the spacecraft is hurting,” Yeomans says. “It’s a credit to the Japanese that they’ve had some work-arounds. It’s the little spacecraft that could.”
During the mission, engineers also suffered the disappearance of the miniature robot Minerva, which was supposed to hop across the surface of asteroid surface but instead was accidentally released to drift off into space.
Despite these setbacks, Hayabusa was successful in returning “stunning images” of Itokawa, Yeomans says. The pictures and other data collected by the craft revealed an unexpectedly crater-free surface and loosely compacted body.
“It seems to be what we call a rubble pile, an object that was blasted apart and is held together by not much more than its own gravity,” he says.
“Mostly we’re just marking time until the sample capsule gets back,” Yeomans adds. “Hopefully the sample will get back.”
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