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Planetary News: Asteroids and Comets (2005)

Hayabusa: Team Re-Establishes Command and Works to Bring its Falcon Home

By A.J.S. Rayl
November 30, 2005
Hayabusa
Hayabusa
Artist's depiction of Hayabusa at asteroid Itokawa Credit: JAXA

The Hayabusa operations team in the Sagamihara Deep Space Control Room   in Japan, have re-established command, control, and communications with its asteroid explorer, which is holding the first samples of an asteroid. But their "falcon" is some 289 million kilometers (180 million miles) away and injured – and whether it will be able to fly home now is in question.

As of today, the team is still not certain as to exactly what went wrong after Hayabusa's second touch-down landing Saturday and whether it will be able to initiate the return trajectory, but they are working hard to bring their bird home.  The good news, Hayabusa Project Manager Jun'ichiro Kawaguchi relayed to The Planetary Society today, is that the spacecraft apparently was not damaged from any of the landing contacts.  

There are, however, issues with Hayabusa's chemical thrusters – on which the spacecraft has been relying to keep its attitude and orientation since the loss of two (of three) reaction wheels. One of the 12 small jet engines sprang a leak, and others aren't providing the thrust they should be. Making matters more intense this week, the team once again lost contact with the spacecraft, this time for nearly a day.

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, arrived in September of this year, and during the last week and a half has flown down to the asteroid twice, finally snaring the much coveted sample on Saturday.

Earlier today, Kawaguchi elaborated on what the team has learned so far. After Hayabusa had completed its touch-down and sample collection last Saturday, November 26, it took off from the surface and successfully decelerated its ascent speed four hours later. After the spacecraft cancelled the ascent speed, it started the three axis stabilization process. But when the Reaction Control System (RCS) thrusters were switched from subsystem A to subsystem B, one of the jets began to leak hydrazine. That caused an "unintended acceleration." The team began an emergency operation to stop the leak by shutting off the "latching valves," and they succeeded. Hayabusa was left in a safe mode and the attitude was stabilized.

There are two RCS subsystems onboard Hayabusa – A and B – which are redundant with each other in case of leaks. Each subsystem can, on its own, handle the three axis stabilization task. That one leak, however, was not the only problem with the RCS. On Sunday, when team members were attempting to bring Hayabusa out of safe mode, they discovered that the thrusts of each of the jet engines on subsystem A was very small.

"The propulsion problem apparently looks like [it was caused by] two distinct events but the details are still under investigation," Kawaguchi said via email. "The second touch-down was done gently with little attitude disturbance. Besides, the leak portion was identified based on the acceleration [of] the spacecraft. Therefore, we do not think the leak derived from the mechanical impact associated with touching-down. The thruster suspected had been used very normally even after the lift-off and we [are] actually very puzzled [by what happened]."

On Monday, November 28, the team lost communication with Hayabusa, but on Tuesday established the beacon link. Still, throughout the day yesterday, the team was having difficulty sending commands and downloading data, ostensibly because of the orientation of the spacecraft.

Today was a new day though, and the team re-established command and communication with Hayabusa. They quickly began troubleshooting with the spacecraft, investigating the cause of the thruster issues in hopes of figuring out  the best way to get the spacecraft onto a trajectory back to Earth.

At this point, Hayabusa's exact location is unknown, although Kawaguchi said that it is "still within several kilometers from Itokawa." Moreover, he added, "there is little chance" they will lose touch with Hayabusa again, at least in terms of where it is now.

Hayabusa's journey has been one of arduous challenges. Since it launched two and a half years ago, the spacecraft has encountered solar flares, the loss of two reaction wheels and its robot hopping lander, MINERVA. And, during its first touch-down landing on November 20, the team lost communication with Hayabusa for three critical hours. At first no one thought the spacecraft had even touched down and that's what was reported globally. But once the team had a chance to review the detailed analysis, they realized their falcon had successfully touched down -- twice, and lifted off, then landed for 30 minutes, until ground control commanded it to take off. The sample collection device, however, did not work during that descent.

Although the data retrieved thus far indicates that the elements of the sample collection device worked last Saturday, scientists cannot be absolutely positive of what exactly Hayabusa picked up until it comes home, if it can get home. This much, however, is certain: no matter how small, the sample harbors secrets about and clues to how the asteroids and planets in our solar system formed.

"The resumption operation of Hayabusa has started," Kawaguchi confirmed. Every instrument except the RCS is in "good health," he noted. "But it may take a certain period [of time] for the spacecraft to resume normal operations." That means it's going to take awhile until they can "commence ion engines operation." Which, in turn, means that Hayabusa is now up against the deadline of its life: it must get into its trajectory for the return to Earth by early December.

At this point, the mission has never been closer – or further away -- from its ultimate objective of bringing back to earth the world's first sample of an asteroid.

"I'll say it again – this is a great adventure in space, a bold and daring mission being conducted in an outstanding manner by JAXA," said Planetary Society Executive Director Louis D. Friedman today. "This rendezvous, targeting, and landing in space is state-of-the-art and puts Japan at the highest of levels in robotic space operation," he added.

"Automated sample return is very difficult and has only been done once before from the surface of another celestial body, by the Russians in 1972 from the Moon," Friedman continued. "It has never been done by the U.S.  The engineering operations are truly exciting and are being conducted brilliantly by what is obviously an excellent team at JAXA/ISAS.  Some of those operations have succeeded and some have not. That is normal in space.  For this first-of-a-kind mission, most observers here in America are amazed that so much has been achieved. No matter what happens from here on out, the wonderful images and close up measurements, and Hayabusa's thrilling rendezvous with Itokawa have already made the mission a scientific success.