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Planetary News: Asteroids and Comets (2005)Hayabusa Does Not Land on Asteroid in First Attempt, But Successfully Delivers Target MarkerBy A.J.S. RaylNovember 21, 2005
Hayabusa – Japan's asteroid explorer – didn't quite land on Itokawa this weekend, failing in its first attempt to touch down and snatch a sample. But it did successfully deliver a target marker to the surface of the asteroid. Even though the team still doesn’t know exactly why their "falcon" did not land on the surface, they are vowing to give it another go in coming days. 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. It is, in fact, the world's first mission to attempt to land on an asteroid, collect samples, and return them to Earth. The spacecraft – which was developed at the Institute of Space and Astronautical Science (ISAS), a space science research division of JAXA -- launched from Japan’s Kagoshima Space Center on May 9, 2003 and arrived in September of this year. The scientists and engineers in the Hayabusa mission control room lost contact with Hayabusa between 6 a.m. and 9 a.m., Sunday morning Japan Standard Time (JST), November 20, and so did not immediately realize what happened. People tuning into the mission via JAXA’s “live” website waited through the hours of silence. After analyzing the data returned by the spacecraft, however, the team found that Hayabusa continued its slow descent following the target marker until it got to within about 10 meters (32.8 feet) of the big rock, and then it autonomously went into safe mode, according to a report issued by the Hayabusa Joint Science Team members that the mission’s Project Manager, Jun'ichiro Kawaguchi, sent to The Planetary Society yesterday afternoon. Instead of landing, the spacecraft apparently cruised above the surface for awhile, until mission control signaled to the spacecraft to abort the landing altogether. While Hayabusa did not succeed in seizing a sample yesterday, the release of the target marker and its safe landing on Itokawa was a significant accomplishment. JAXA's Yasunori Matogawa, and Kawaguchi, of ISAS, announced the news at a press conference held Sunday afternoon around 4 p.m. JST at ISAS headquarters in Sagamihara City, Kanagawa Prefecture, about 40 kilometers (25 miles) west of Tokyo. The spacecraft, they said, released the target marker when it descended to an altitude of about 40 meters (131 feet) above the asteroid, and at 5:46 a.m., Sunday, November 20 (JST) JAXA received the signal that Hayabusa had carried out its task successfully. This particular target marker carried special cargo – an aluminum sheet bearing 880,000 signatures gathered by The Planetary Society of Japan from people around the world – and delivered it to the surface. Moving at a velocity of 10 centimeters (about four inches) a second, the target marker landed about six and a half minutes after it left Hayabusa, settling down just as planned in the nice flat region that the team dubbed Muses Sea (after the original generic name of the spacecraft MUSES-C). Since signals take around 17 minutes to get from Earth to Hayabusa, the spacecraft was on its own once it began to carry out the series of commands for Sunday's attempted touch-down. Its autonomous navigation relies on the Optical Navigation Camera and Light Detection and Ranging (ONC/LD&R) instrument, which measures the distance to and the shapes of the asteroid surface. Hayabusa continued to descend toward the surface, "and successfully changed its attitude control to terrain alignment autonomous control using Laser Range Finder," according to the Hayabusa team’s report. If everything had gone as planned, the spacecraft would have continued on to a "soft" landing, touching down on the surface just long enough for its sample collector to reach out and seize just one gram of top soil, and then return to its home orbit around 7 kilometers out. When Hayabusa descended to below 17 meters (55.7 feet), it stopped firing its engines and started into a freefall descent to the surface, according to the team's report. "We were watching it via Doppler," they wrote. "But no touch-down occurred for surprisingly 30 minutes, during which the descent continued at very slow speed of about 2 centimeters [.78 inch] per second. We estimate Hayabusa drifted at very low altitude along the surface. Therefore, Hayabusa did not touch down [on] the surface, but reached approximately below 10 meters [32.8 feet].” Hayabusa cruised above the surface long enough for part of it at least to heat up to around 100 degrees Celsius (212 degrees Fahrenheit), according to Kawaguchi. Concerned about the temperature, the team sent up a command to Hayabusa to fly away quickly. "We directed a command to Hayabusa to make an abort, since the sub-spacecraft point might have shifted so much from the intended [landing] area," according to the report. Hayabusa heeded the command and rose to about 100 kilometers (about 62 miles). The team is not yet exactly sure why Hayabusa fell into safe mode, but they believe it is because of an "attitude anomaly" that occurred close to the altitude of about 10 meters or so. It may be because Hayabusa failed to keep its attitude right just before touch-down and autonomously decided to put itself into safe mode in order to save fuel. Kawaguchi described this event "un-understadable," but said that "the details are under investigation." Meanwhile the team's recovery of Hayabusa was performed successfully, Kawaguchi said, and the team will be testing the instruments to make sure each is still in good working order. The fact that Hayabusa did not succeed the first time it tried to swoop down and grab its prey came as little surprise to most who have been following the mission – not because Japan is a fledgling country in space exploration, but because what they're trying to do, rather have the spacecraft do autonomously, from 180 million miles away, is incredibly complex, with each and maneuver involving myriad elements that all have to be working in sync. Hayabusa is as ambitious a mission as they come – and from a country young in space exploration – it probably would have been considered a miracle if it had succeeded in every objective. During the two and a half years since it launched, Hayabusa has encountered more than its fair share of trouble, not the least of which were several life-threatening solar flares encountered en route to Itokawa. Then, on July 31 of this year, shortly before Hayabusa's arrival at the asteroid, the X-axis wheel, one of three reaction wheels onboard that control the spacecraft's orientation and are used to point instruments, antennas, or subsystems at chosen targets, just stopped. The spacecraft was designed to function just fine with the two remaining reaction wheels, Kawaguchi told The Planetary Society in an interview in September, it was able to resume attitude stability and the spacecraft had been operating normally since. Since the JAXA spacecraft arrived at Itokawa last September, however, Hayabusa has suffered the loss of a second reaction wheel. A couple of weeks ago, Hayabusa released its tiny lander, Minerva, at the wrong time, sending the tiny, coffee-can sized robot floating off into space, instead of hopping around the asteroid for up to 36 hours taking pictures and collecting temperature data as was the plan. Now the obstacles are looming large for Hayabusa as it enters what must be the final days of its mission at the small asteroid, which measures just 549 meters (1,800 feet long) by 180 meters (590 feet) wide. Although Kawaguchi told The Planetary Society earlier that the mission could probably succeed with only one reaction wheel if it came to that, there is now concern now about whether or not the asteroid explorer can continue to keep the attitude needed in order for Hayabusa to successfully snatch a sample due. Meanwhile, Hayabusa is also racing the clock. The countdown to return to Earth is on, for the spacecraft needs to propel itself away from Itokawa by early December in order to place itself in the right trajectory to reach Earth. But there is a lot of hope and confidence remaining amongst the team members, and Hayabusa may swoop down and try again as early as next Friday, November 25. "The project looks positively at the next opportunity, since almost every difficult step was now identified to function normally," the team stated in its report. This time, they noted, "the guidance and navigation to the intended point was performed quite well with the residual speed of almost several millimeters per second, that is the walking speed of worms." One sample returned safely to the Australian outback in June 2007 is all it would take for this intrepid group to rightfully claim full mission success. Still, Hayabusa has already contributed reams of new data about asteroids like Itokawa, as well as data on ion propulsion and other technologies created by the Japanese especially for sample return missions. At the press conference, Matogawa evaluated the Hayabusa mission so far as the great success that will open "a new gateway" to Japan's space exploration. "This is an incredible adventure unfolding at the asteroid -- and the sheer boldness of the attempt with the care obviously being taken in carrying it out is breathtaking," said Planetary Society Executive Director Louis D. Friedman. "We are on the edge of seats, with admiration and suspense, hoping it will work out." Taksuku Iyori of The Planetary Society of Japan contributed to this story. . |
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