Japanese spacecraft returns from asteroid mission, years overdue
Tuesday, June 29, 2010
By the time its odyssey ended this month in the Australian outback, the spacecraft Hayabusa had been gone three years longer than planned, lost its main engine, disappeared from all interplanetary notice for more than seven weeks and may have failed to perform its main mission.
Yet the voyage was justifiably and immediately hailed as the stuff of legend. Against all odds, the Japanese space agency, with support from NASA, managed not only to bring Hayabusa back to Earth but also to do something never done before: take a sample from the surface of a distant asteroid and bring it home for study.
"Really, when we saw it land, we could not believe what had happened," said Norimitsu Kamimori, the Washington representative of the Japan Aerospace Exploration Agency, or JAXA. "We hoped, but we never really thought Hayabusa would make it back."
The American public is understandably focused on the feats of NASA and missions funded by American taxpayers. But the exploration of space has become an increasingly international affair, and several dozen nations have space programs of their own or in conjunction with partners.
The Japanese space agency is hardly the largest, and its program is far from the most ambitious. But the Hayabusa mission now has a special place among space-faring nations; its accomplishment ranks somewhere between the life-or-death engineering that brought Apollo 13 back to Earth safely and the long-lived rovers Spirit and Opportunity, which were designed to last 90 days on Mars but are still beaming information and photos back after six years.
Anthony Carro, NASA's program executive for Hayabusa, called the return "an incredible feat." Much of the spacecraft was crippled, he said, "but the Japanese flight controllers were ingenious in figuring out ways to combine the powers of what they had, and they brought it back."
NASA project scientist Donald Yeomans called the return "well beyond remarkable and into the miracle stage."
The odyssey begins
The Hayabusa mission launched with great fanfare in 2003 and headed for the asteroid Itokawa, an irregularly-shaped rock that orbits between Earth and Mars, far away from the crowded asteroid belt between Mars and Jupiter.
It was the most ambitious Japanese space mission to date, and it used both a traditional chemical-fueled rocket engine and additional ion engines, a novel use of microwave technology that moves the spacecraft by heating xenon gas. It's a very energy-efficient way to travel, and that came to be extremely important in the odyssey.
The spaceship reached the asteroid more than two years later, after traveling 1.25 billion miles. At that point in its asymmetrical orbit around the sun, the asteroid was almost 200 million miles from Earth.
Itokawa is often compared to an inflated baked potato about a third of a mile long. It has virtually no gravitational pull, which is what made feasible the goal of touching down, picking up a sample and flying off. But it was difficult, since the asteroid was spinning. The spacecraft carried an instrument akin to a pellet gun that was designed to fire into the asteroid's silicon- and iron-based rocks. Once the gun was fired, the plan was for Hayabusa to snag some of the flakes kicked up from the rocks.
As explained by Kamimori and JAXA releases, what happened after Hayabusa caught up to Itokawa was a series of technical problems that seemed to doom the mission. First, an attempt to send the spacecraft's small robotic rover Minerva to the asteroid to take pictures and temperature readings failed. The rover, which was powered by its own small engines, never touched down on the asteroid and inexplicably drifted off into space and vanished forever, according to JAXA mission control.
Then, Hayabusa landed on Itokawa and stayed for 30 minutes, but the pellet gun didn't fire. Researchers hope that some asteroid dust was pulled into the sample box, but it's almost certain that no rock flakes were collected.
Because of the pellet gun malfunction, JAXA decided to try landing again. But when the spacecraft touched down, one of the main chemical engines controlling its attitude sprang a leak. That led to a series of malfunctions that climaxed in a total blackout of communications with the craft as it slipped off the asteroid and into space.
After seven weeks the spacecraft was just about given up for lost when NASA's Deep Space Network, which was supplementing JAXA's communication capacities, made contact. It took 16 months to get Hayabusa back under JAXA's full control and to rev up the ion engines that would serve as the central power for the craft.
In addition to the fuel leak that knocked out the main chemical engine, the batteries that stored energy from the craft's solar panels also malfunctioned. The ion engines are not nearly as powerful as the ones based on more traditional fuels, but at least they were still working.
"Technical development doesn't always go as you wish. There were times I almost felt defeated and wondered about waving the white flag," Hitoshi Kuninaka, designer and engineer for the ion engine, told a JAXA interviewer just before the landing back on Earth. "Hayabusa has overcome many obstacles. In that sense, I feel I raised Hayabusa's ion engines little by little, almost like a newborn baby, by calming and cheering them on."
A safe landing
By the time Hayabusa was closing in on Earth, the ion engines were just barely working. But with help from reentry specialists at NASA's Jet Propulsion Lab, JAXA engineers steered Hayabusa in as planned. The spacecraft was filmed dramatically burning up as it streaked into the upper atmosphere, but its round-bottomed reentry capsule (about the size of a small stack of dinner plates, it contains the box of samples) floated down in the outback, tethered to a parachute.
The sample container is back in Japan now, in one of a series of clean rooms where it will be examined and then opened, sometime in the next few weeks. A modified CAT scan will first be used to search for material inside the box, but officials think they'll need to use a powerful scanning electron microscope to determine whether any dust particles were collected and made it back.
Yeomans, a manager at NASA's Near-Earth Object Program Office, said that even if just dust particles are found, "we'll be looking at leftover debris from the early solar-system formation process. . . . An asteroid like this was first formed maybe 4.6 billion years ago, and from what we can tell probably was broken apart and reassembled since then. Nothing on Earth has the kind of early solar system characteristics we could be looking at."
The JAXA sample study team, which includes one NASA member, will have sole control over whatever is in the capsule for one year. After that, any samples will be distributed to interested scientists around the world.
In the acclaim following the recovery of the sample box, the new prime minister of Japan, Naoto Kan, announced that funds for a second Hayabusa would be raised. Japan has sent seven astronauts to the international space station and built the Kibo science lab, an important part of the station. But nothing has attracted as much attention to the Japanese space program.
"So many instruments failed on Hayabusa, but we still brought it back to Earth and it may have some dust samples from Itokawa," said Kamimori. "This is why Japanese people were so excited by what happened and why they think it was a great success."