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Planetary News: Asteroids and Comets (2005)Hayabusa: Japan's Asteroid Mission Prepares to Drop Lander and Rehearse for Two "Soft" LandingsBy A.J.S. RaylNovember 2, 2005
Japan's Hayabusa is preparing to drop its tiny lander, Minerva, on the surface of the asteroid Itokawa Friday, and, at the same time, rehearse for two "soft" landings and sample collections to take place later this month. Hayabusa is the Japan Aerospace Exploration Agency's $170-million-dollar mission to this near-Earth asteroid -- and the world's first mission to attempt to land on an asteroid, collect samples, and return them to Earth. After overcoming a host of obstacles, including several life-threatening solar flares on its 1-billion kilometer journey (about 620 million miles), the JAXA spacecraft finally arrived at Itokawa in September. Currently, Hayabusa -- which means "falcon" in Japanese -- is "hovering" 4.4 kilometers (about 2.7 miles) from Itokawa, as team members put the spacecraft through its final paces and instrument calibrations in preparation for the coming events this month. The schedule is as follows:
"Gutsy is the word for this mission," Donald K. Yeomans, senior research scientist at the Jet Propulsion Laboratory (JPL) and the U.S. project scientist for the mission, told The Planetary Society in an interview yesterday. "It's the first asteroid sample return -- which for the Japanese is remarkable -- especially when you look at the previous complex mission they did successfully -- the Halley's comet flyby in the 1980s." Indeed, Hayabusa is a complex mission. "It's going to be releasing a small ‘hopper’ lander, then later the spacecraft itself will touch down two times to gather samples, and then go back up to its ‘home’ orbit all autonomously, because they can't joystick this thing," Yeomans expounded. That's because it takes radiowaves about 17 minutes to travel from the spacecraft back to Earth, far too long for the operations team on Earth to send any additional commands to the spacecraft once the action begins. All these various maneuvers are, therefore, "dangerous," said Yeomans. "One false step and they could set that spacecraft on its nose and that's the end of this mission." But successful completion of all those maneuvers is what it will take for Hayabusa to meet all of its mission objectives. Thus far, this falcon's flight has been nothing less than impressive, and Team Hayabusa is doing everything it can to improve the odds for its daring mission.
Since its arrival at Itokawa in September, Hayabusa has been examining the asteroid up-close, conducting global mapping of the surface features, collecting data to determine the surface composition, and looking for the best places to drop Minerva and put the spacecraft down later this month. While landing on an asteroid is tricky business, landing on this particular asteroid could be even trickier than anticipated. Of most concern is the fact that the images Hayabusa has taken during the last 6 weeks show that Itokawa is an incredibly rocky, boulder-strewn asteroid "that is anything but smooth in some places," as Yeomans put it. Moreover, it's not exactly large enough to leave much margin for error. According to the latest Japanese measurements, Itokawa is only 540 meters by 310 meters by 250 meters (about 1,800 feet by 1,000 feet by 820 feet), and it doesn't really look like your basic potato-shaped asteroid. Rather, it's kind of, as Yeomans described it, "a deformed potato shape." Still, the JAXA team is ready to rock. By all accounts, the calculated risks the Japanese are taking will be worth all the white-knuckle moments and much more if they make it happen. "Hayabusa has everything -- ion drive engines, rendezvous with an asteroid, touch-and-go sampling, a return capsule to Earth -- and they have tested technologies unique to their system," Yeomans pointed out. Louis D. Friedman, executive director of The Planetary Society, agreed and added: "If successful, the Hayabusa mission will be for Japan an achievement equivalent to the former Soviet Union's first landing on the Moon or the first landing on Mars by the Americans." When Hayabusa aims its first target marker at the asteroid's surface on Friday, it will function as a beacon that reflects in response to a signal from the spacecraft, helping guide the spacecraft to the best drop-point to insure Minerva gets to the chosen landing site. Tucked inside this first target marker is an aluminum sheet bearing the names of 880,000 Earthlings gathered by The Planetary Society of Japan in 2002, to be a part of Itokawa for a long time to come. "That [sheet of names] will sit on the surface of Itokawa for a billion years or so," Yeomans estimated. Since there is very little gravity on Itokawa, Minerva -- which weighs just 519 grams (a little more than 1 pound) and is about the size of a large coffee can -- should settle gently down onto the asteroid. Given that this asteroid boasts many more rocky areas and boulders than anyone anticipated, however, the real white-knuckle time during this operation will come with the timing of the release. Once on the surface, if all goes according to design, the solar-powered, box-shaped robot will take advantage of Itokawa's very low gravity and hop around the asteroid taking images with three miniature cameras, collecting composition data with thermal probes. Minerva will relay the images and data to Hayabusa whenever the two spacecraft are in sight of one another. "Its lifetime is supposed to be three asteroid days, which is about 36 hours," Yeomans said. But, “there are many concerns," Hayabusa Project Manager Jun'ichiro Kawaguchi said via email. "The surface temperature is high, more than 100 degrees Centigrade [212 Fahrenheit] probably. And how long it survives is questionable." If Minerva's hopping journey is even partially successful, JAXA will log another space exploration first with this mission by putting the first 'space hopper' in action. (The former Soviet Union launched hoppers on the Phobos mission, but both Phobos 1 and Phobos 2 failed to arrive safely on Mars and so those hoppers never saw actual use.) On November 12 and November 25, Hayabusa will confront the most difficult of its tasks -- making the "soft" landings to "snatch" one gram of Itokawa's dust. On November 12, the spacecraft will touch-down in the largest flat area on the asteroid, which lies near the midsection, and which the JAXA team has dubbed Muses Sea (a word-play on the generic label of the spacecraft -- MUSES-C -- before it launched and was renamed Hayabusa). Two weeks later, on November 12, Hayabusa will touch-down one more time for a second sample collection in another smooth area the team is calling the Woomera Desert, which is located at the tip end of Itokawa, where the terrain is broad and flat. How, exactly, will Hayabusa collect these samples? "There's a cone or horn-shaped device on the spacecraft -- sort of like a [stubby] megaphone or a scoop, where the end is like a cone and the central part is a cylinder," Yeomans explained. "They fire a pellet down the center of the scoop and as the ejecta comes up it funnels back into the chamber." Blow by blow, "Hayabusa will come down very slowly, at about 1/10th of a meter per second," Yeomans elaborated. "As soon as the front end of the cone touches the surface, a tantulum pellet will be fired into the surface at 300 meters per second and the ejecta from that cratering effect is captured by this megaphone or horn-like device and is then brought into the sample chamber. Because there is hardly any gravity, the ejecta should just rise up and be captured in the chamber. The chamber will then rotate and close, with the sample inside." The whole process will take a matter of seconds. "It's a one-second touch-down," said Yeomans. "It just goes -- 'boink' -- touches the surface, collects the sample, and goes back up. It's all autnomous, the touch ‘n go. It has to be. Hayabusa will then return to its "home orbit," several kilometers above the surface.” If the tasks ahead weren't unnerving enough, the mission has encountered some troubles in recent weeks, the most significant of which is the loss of the second of three reaction wheels that are used to maintain attitude and orientation of the spacecraft. Tasuku Iyori, of The Planetary Society of Japan, has conveyed via e-mail that the mission control team in Sagamihara has confirmed that the two malfunctioning attitude control wheels will not impact Hayabusa's sampling activities in any way. "They do have one functioning wheel, and so what they can do -- and are doing -- is use one wheel and their hydrazine thrusters to keep the spacecraft steady," Yeomans confirmed. Meanwhile, everything else appears to be working the way it should. "The instruments are all functioning well, although they are not all calibrated yet," informed Yeomans. "Eventually we will get the calibrated spectra and calibrated images, and this is going to turn out to be a remarkable mission." Although this mission is well behind where a similar NASA mission would be, "they have 1/10th the manpower and they're doing it." Yeomans said. "I think of this mission as a U.S. mission in slow motion. They've got scientists doing operations and engineers helping out, and everyone's working very hard. This is a seat-of-the-pants operation that's being handled by just a small number of people from what I can see, including project manager Jun'ichiro Kawaguchi, and project scientist Akira Fujiwara, and a handful of others. Even so, the images don't lie. Those that I have seen so far are really quite extraordinary." As Yeomans views it, the Hayabusa asteroid sample return mission is "the next giant step forward" in understanding the role of near-Earth asteroids in the origin of the solar system, their potential threat to Earth, and the future use of their raw materials to expand human presence beyond Earth. "Near-Earth asteroids are easier to land on than the Moon itself, some of them, and they're far more rich in minerals," he pointed out. "If you're going to build structures in space, you're not going to build them on the ground and launch them, you're going to look for raw materials up there, and asteroids provide some ready supplies of minerals, metals, and possibly water." Like most major missions these days, Hayabusa features something of an international team. In addition to Japan's Hayabusa team, there are 9 Americans on the team, including Yeomans, and 10 scientists from other countries. Several years ago before the mission launched, Yeomans and others at JPL and NASA provided JAXA and its Institute of Space and Aeronautical Science (ISAS) division, with the ephemeris, a table that shows the coordinates of a celestial body at a number of specific times during a given period -- essentially "directions" on how to get to the asteroid named for Hideo Itokawa, generally regarded as the father of Japan's space program. And, not surprisingly, NASA is tracking the spacecraft with the Deep Space Network (DSN) and the Americans there are providing some back-up navigation assistance. That noted, however, Hayabusa is not relying on NASA for the navigation. Once Hayabusa arrived at Itokawa, "it's been Japan's show," said Yeomans. "They really are in the driver's seat, and that's the way they want it." Hayabusa has had its share of skeptics, mostly because of the enormous risks involved in such a complex and tricky mission as this one, launched and managed by a country not as experienced in space exploration as the United States or Russia. The question now bounding through the minds of many space enthusiasts is: Are they going to be able to do it? Can the Japanese pull off this "gutsy" mission? "Yes, I think they will," opined Yeomans. "So far, they are pulling it off. I'm a believer now -- and hats off to them." If all goes as planned -- or at least as well as it has gone so far, Hayabusa will head for home in December, samples in tow. Its return capsule is slated to parachute to a landing in the Australian outback in June 2007. That accomplishment would raise Japan's profile in the space exploration logs and demonstrate that Japan is a force with which to be reckoned in this business of space. "If they do bring a sample back, that's going to be extraordinary," said Yeomans, "especially for $170 million!" "Whether they do or don't pull it off, it has already been an amazing mission that has been brilliantly performed," added The Planetary Society's Friedman. "Whatever happens from here on, they have done well."
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