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Probe to take another try at snaring bits of asteroid BY STEPHEN CLARK SPACEFLIGHT NOW Posted: November 25, 2005 Japan's bold Hayabusa asteroid explorer has one last shot at success in the planned late Friday descent to the surface to collect samples for return to Earth. The attempt will come three days after officials went back on initial reports and declared the probe touched down on Itokawa for up to thirty minutes last weekend.
The high speed impact will kick rocky material into a 16-inch funnel that will route the specimens into a collection chamber that will ferry the samples back to Earth and through the planet's atmosphere to a parachuted landing at the Woomera test site in the Australian outback in the summer of 2007. Friday's collection attempt is likely to be the last for the Hayabusa mission, which is facing a fuel crisis after a pair of reaction wheel failures earlier this year caused more propellant to be burned in attitude control maneuvers. Problems also plaguing the $100 million mission include an unwavering deadline just a few weeks away to depart the vicinity of Itokawa for return to Earth. Hayabusa must leave by early December to make it home in 2007. In addition, just one target marker remains aboard the craft. This tool is critical to the delicate descent to the surface because it gives cues to the autonomous navigation and guidance systems. The craft originally carried three navigation aids, but two were deployed during a rehearsal earlier this month and a first sampling attempt last weekend. The original strategy for the mission called for a pair of sample runs, and the first half of that plan was realized overnight November 19 when Hayabusa was commanded to move toward the asteroid in an effort to reach the surface. The probe reached within an altitude of 55 feet, when the guidance system began drawing on range and closure rate data provided by the laser range finder. At this point, the massive stream of telemetry information flowing to control rooms on Earth was reduced to just a trickle, but teams could continue to follow the progress of the maneuver through low bandwidth Doppler data.
After controllers regained full communications and command of Hayabusa, they began to downlink more data to get a better picture of the events that transpired last weekend. The new understanding by the project team is that the probe touched down on the surface of the asteroid for up to thirty minutes after softly bouncing twice at about four inches per second before settling to a standstill. No damage from the unexpected landing has been detected. This finding was confirmed by the laser range finder, whose data was transmitted back to Earth after Hayabusa was taken out of safe mode. Information on the landing was not available in real time because two-way communications with the spacecraft was switching antennas from NASA's Deep Space Network to Japan's Usuda station. The ground team sent the command for an emergency ascent after engineers recognized that the sampling attempt was likely a failure. Hayabusa went into safe mode at this time, and it took two days to fully recover control of the probe, which was necessary to downlink the recorded data needed to decipher what actually happened. Despite becoming the first spacecraft to successfully take off from an asteroid - and even the first to depart any celestial body outside of the Earth-Moon system - Hayabusa did not succeed in its primary mission to collect specimens from Itokawa. A sensor designed to detect potentially unsafe obstacles triggered an abort of the sampling procedure, but did not stop the descent. Hayabusa has spent the past few days gradually moving closer to Itokawa, and by late Thursday it had arrived just three miles away to set up for the final try to gather samples. The Friday attempt has been on the schedule for weeks now, and NASA's worldwide group of dish-shaped antennas known as the Deep Space Network had already allotted time for the mission during this period. Officials wanted to take advantage of that opportunity because it was unclear if it was possible to have another such opening before Hayabusa must begin its voyage back to Earth. |
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