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Planetary News: Asteroids and Comets (2005)Hayabusa: Got Sample? Yes!By A.J.S. RaylNovember 28, 2005
Japan's asteroid explorer, Hayabusa, touched down on Itokawa Saturday, November 26, and grabbed the grail – a sample of surface soils and dust. This marks the first time any spacecraft from any country has touched down on an asteroid and picked up a sample, a milestone that moves Japan into the space exploration spotlight. During its first attempt to collect a sample on November 20, Hayabusa actually touched down twice and then landed for 30 minutes, but the collection procedure never initiated and the mission team had to command its falcon to fly up and away from the asteroid. On Saturday, however, Japan's bird swooped down and captured its prey, despite early media reports to the contrary. "It touched down on the asteroid again and succeeded in collecting [the] sample by shooting two projectiles at the same time," Hayabusa Project Manager Jun'ichiro Kawaguchi confirmed for The Planetary Society in an email this weekend. Hayabusa – which means "falcon" in Japanese -- is the Japan Aerospace Exploration Agency's $170-million-dollar mission to the near Earth asteroid named after the "father" of Japan's space program, Hideo Itokawa. The world's first spacecraft to attempt to land on an asteroid, collect samples, and return them to Earth was developed at the Institute of Space and Astronautical Science (ISAS), a space science research division of JAXA. It launched from Japan’s Kagoshima Space Center on May 9, 2003 and arrived in September of this year. The mission team members are still awaiting more detailed data recorded during Hayabusa's exciting touch-down Saturday and in coming days plan to further verify the sampling. “They have telemetry suggesting the pellets [in the sample collection device] fired and so it’s looking pretty good that the sample was captured,” offered Donald K. Yeomans, senior research scientist at the Jet Propulsion Laboratory (JPL) and the U.S. project scientist for the mission. Currently, this much is known: Hayabusa started its last descent phase from the altitude of 1 kilometer (.62 mile) above Itokawa with a command from Earth around 10:00 p.m., November 25, Japan Standard Time (JST). The Sagamihara Deep Space Control Room was “filled with determination,” according to JAXA’s Associate Executive Director Yasunori Matogawa, who reported on Hayabusa’s “longest day” on the agency’s website. Around 6:00 a.m., Saturday (JST), Hayabusa began the vertical descent down the MUSES Sea landing site (so dubbed for the generic name of the spacecraft, MUSES-C), and around 6:20 a.m., with all systems seemingly operating normally, the team at Sagamihara Deep Space Control Room sent a command to continue descending. As Hayabusa continued its flight down to the asteroid, it homed in on the Target Marker it dropped onto the surface of Itokawa before its first soft landing on November 20. The team decided not to drop a second Target Marker as was originally planned, because there was concern that Hayabusa might get confused if two markers glowed when the spacecraft “flashed” them with its marker light. It turned out to be the right call. From an altitude of just 35 meters (about 115 feet) above the asteroid, the spacecraft switched from its light detecting and ranging instrument (LD&R) to the laser range finders (LRFs) just like it was supposed to. Around 6:24 a.m., Saturday, the camera onboard Hayabusa snapped some remarkable images of the MUSES Sea that showed a tiny glow that was the Target Marker, “wow-ing” mementos that should surely bring a big smile to the faces of the 880,000 supporters from 149 countries whose names, gathered by The Planetary Society of Japan, are etched on an aluminum foil sheet tucked inside as a kind of greeting card from Earth for any visitors that may happen upon the asteroid in the next billion years or so. When the spacecraft got to just 14 meters (about 46 feet) above the asteroid at about 7:00 a.m., it hovered, adjusting its own attitude to the terrain of Itokawa by controlling attitude to keep its vertical axis (Z axis) perpendicular to the inclined slope of the surface. At this juncture, communication between the control room and Hayabusa was switched to beacon mode from telemetry transmission. Team leaders “breathlessly” watched the Doppler data, while listening to the altitudes called out by laser ranger finder (LRF) staff, according to Matogawa. At 7:04 a.m., the mode of LRF was switched from range finding to sampler control mode and Hayabusa went in for the touch-down and sampling. About three minutes later, the samples were collected via a device that is shaped like "a stubby megaphone," where the end is like a horn-shaped scoop and the central part is a cylinder, as Yeomans described it. As soon as the front end of the horn-shaped scoop touched the surface Saturday, two tantulum pellets were fired into the surface at 300 meters per second, at an interval of .02 second, and the ejecta from the cratering effect was captured inside the scoop and brought into the sample chamber. Since there is hardly any gravity out at Itokawa, the ejecta, theoretically, just rose up and into the chamber, which then rotated and closed, with the sample inside. The whole process took a matter of seconds as the spacecraft touched down in a "soft" landing, snatched its sample, and took off again, all on its own, flying autnomously, because commands take around 17 minutes to get to the spacecraft. At 7:35 a.m. (JST), the monitor in the Sagamihara Deep Space Control Room flashed three green letters on the screen – three letters that signified Hayabusa had snatched its sample. “The room was roaring,” said Matogawa. Hayabusa's daring flights this past week have made for some real white-knuckle moments for the team members and confusion for the media. During the first sample collection attempt on November 20, the team lost communication with its charge for three critical hours and wound up having to bring the bird back from safe mode and from hundreds of kilometers away. On Saturday, Hayabusa experienced some trouble with its chemical thruster system during the descent and had to switch to a redundant system to carry out the touch-down and sampling operation. The data needed to confirm the successful capture was not immediately available, and initial media reports conveyed that Hayabusa had not grabbed a sample. The Hayabusa team, however, was able to pretty quickly analyze the telemetry data and Saturday afternoon announced that "a series of sequences for sampling was successfully done." Hayabusa then flew up to several kilometers altitude with normal solar paddles power, spacecraft attitude. “The spacecraft [went] into a safe mode again," reported Kawaguchi, due to "its attitude dispersion during ascent." Throughout the rest of the weekend, the mission team in the Sagamihara Deep Space Control Room worked to recover the sapceceraft. Hayabusa, however, remains in safe mode, which is, as always, causing additional concern for team members. “If we can get out of safe mode things will look a lot better,” said Yeomans in an interview earlier today. “It’s not so unusual . . . it’s been there before and there’s a fairly high probability it will get out, but it took three days last time.” At this point, Hayabusa is currently in its “home” orbit around 6.5 kilometers (about 4 miles) from Itokawa. All instruments onboard are functioning well, although, Kawaguchi added, "the spacecraft was a little injured at the previous touch-down and the project team is currently [also] working on resuming and fixing [that] problem." To complete its bold mission, Japan's falcon must fly its precious cargo home. That part of the mission is set to begin in early December. Meanwhile, in coming days, more detailed data will be downloaded to the mission control team at ISAS in Sagamihara. Based on its analysis, the team will decide then whether to go for another touch-down and sample collection or to call it a day and head for home. If they get the verification they expect is coming in that data, “I think they’ll probably head for home,” said Yeomans. And, if all goes as planned, the sample will return to Earth, parachuting to the ground in the Australian outback in June 2007. |
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