Japan's Hayabusa spacecraft suffered another serious setback on Sunday, failing to land on asteroid Itokawa and capture dust from its surface.
After approaching to within metres of the 500-metre-wide asteroid, the spacecraft suffered a malfunction and temporarily lost contact with Earth. When the communication link was re-established, several hours later, the probe had drifted much further away from its target.
"So far the result of the first sampling attempt is somewhat unclear," Kazuya Yoshida, a member of the mission team at Tohoku University told New Scientist. "But it is less likely that the touchdown was conducted as expected."
The spacecraft is thought to have successfully landed a "target marker" – a small metal ball – on Itokawa, having releasing it from a distance of 40 metres away. The metal ball was to help identify the point where the probe would briefly touch down, before firing a pellet into the surface and catching the resulting debris. The plan was to return the first-ever asteroid samples to Earth.
After placing the target marker, the spacecraft moved itself to within 17 metres of the asteroid's surface at 2030 GMT on Sunday, in preparation for touchdown. But Hayabusa then suffered a glitch that left it unable to confirm its altitude, and also lost contact with Earth. These problems may have been caused by unexpected overheating of the onboard instruments, and mission members are now checking to see if they are still working. The spacecraft resumed transmission at 0030 GMT but by then had drifted far away from the asteroid.
"What we are puzzled about now is why the touchdown did not occur," says mission project manager Jun'ichiro Kawaguchi. He says the mission went off track when "there was only free fall motion planned". Before that, the spacecraft had successfully used its navigation and guidance system to position itself above the asteroid at the careful pace of just millimetres per second. "That is the walking speed of worms," he says.
The landing trouble may have been caused in part by the fact that the spacecraft is firing fuel thrusters to point itself - a contingency solution devised following the failure of two of the craft's three stabilising reaction wheels. While the thrusters were decelerating the spacecraft, it may have drifted horizontally. "The magnitude is small but somewhat significant in a very small gravity environment," Kawaguchi told New Scientist.
Kawaguchi says the spacecraft may attempt another touch down on Friday: "There is one more target marker left, so I'd like to try one more time."
If the mission succeeds, and returns the first ever asteroid sample to Earth, scientists will use the material to learn more about the primordial solar system.
But Hayabusa has already suffered a series of hiccups. On 12 November, the spacecraft lost contact with a small robotic rover – called Minerva – that was designed to hop around the surface of the asteroid capturing images and taking temperature readings. Minerva is thought to have missed the asteroid entirely and drifted off into space.
A practice descent was also aborted on 4 November when the probe sent an "anomalous signal" back to mission control.
Itokawa was discovered in 1998 and is named after the Japanese rocket scientist Hideo Itokawa. Hayabusa was launched in May 2003 with a budget of 12.7 billion yen ($100 million) and is scheduled to return to Earth mid-2007. The spacecraft must leave the asteroid by early December 2005 in order to make it safely back to Earth, but mission controllers are not yet sure they will return the craft if the asteroid sampling fails.
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11:17 21 August 2008
