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Planetary News: Asteroids and Comets (2005)

Hayabusa: Japan Conducts Landing Test at Asteroid Itokawa

 

By A.J.S. Rayl
November 14, 2005
Minerva hopper and Hayabusa's shadow at Itokawa
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A photo of the asteroid Itokawa from the Hayabusa spacecraft on November 12, 2005 shows the Minerva lander (dot inside the yellow circle, and detail inside the yellow square) near the asteroid. Minerva was released and activated successfully but failed to land on Itokawa. The dark bow-tie shape on Itokawa is the shadow of Hayabusa. Credit: ISAS / JAXA

This weekend the Japan Aerospace Exploration Agency's Hayabusa conducted its second test descent to the asteroid Itokawa in preparation to land and collect samples, and the agency announced that it “performed the touch down test with success.”

The spacecraft first attempted this descent test on November 4, but aborted mid-way through when it was several hundred meters from the surface. Since it takes about 17 minutes for messages to be relayed from the mission controller on Earth to Hayabusa, the spacecraft must carry out the descent and landing tasks autonomously, and so once Hayabusa begins a flight down close to the asteroid, it is on its own. For that reason alone, the mission’s success over the weekend was no small feat.

Not every item on Hayabusa’s agenda this past weekend, however, met with success. During the descent activities, Hayabusa released MINERVA, a tiny lander that was to hop around the asteroid taking measurements and pictures. All went well with the release, but the lander did not get to its destination on the surface. Hayabusa Project Manager Jun’ichiro Kawaguchi told The Planetary Society in an email interview over the weekend that the data they had obtained indicated that Hayabusa was not getting all the necessary information at the right time from its instruments and as a result “MINERVA was released with the ascent velocity slightly higher than escape velocity.” He also said they had no “definite evidence” that MINERVA hit the surface.

Although MINERVA was unable to carry out its duties on the asteroid, the team was able to communicate with the lander after its release, said Kawaguchi, and  was glad the robot “functioned normally” and “was delivered to the Itokawa vicinity.” Moreover, “the MINERVA camera photographed Hayabusa as it separated” and the Hayabusa camera captured MINERVA flying away. Both images, he added, were "transmitted and relayed to the ground” and will be released soon.

Hayabusa – which was developed at the Institute of Space and Astronautical Science (ISAS), a space science research division arm of JAXA -- launched from Japan’s Kagoshima Space Center on May 9, 2003. It overcame a number of obstacles during its 1-billion kilometer (621 million mile) journey, including several life-threatening solar flares that slowed it down a bit. But the $170 million mission arrived at Itokawa just a little worse for the wear in September of this year, and has since managed to log several firsts in space exploration as it has worked to carry out the mission objectives.

Now some 289,574,800 kilometers, or 180 million miles from Earth, Hayabusa will confront its most difficult challenge yet in coming days: attempting the first “soft” or touch-down landing to snatch a sample of Itokawa’s surface soils. Even though the low gravity out there makes landing more like a docking, a lot of elements and instruments have to be working in synch, and given that Itokawa is only 540 meters by 310 meters by 250 meters (about 1,800 feet by 1,000 feet by 820 feet) and much rockier than anticipated, there is not much of a margin for error.

Meanwhile, mechanical issues are making things more difficult now for the spacecraft. Because two of the spacecraft’s three reaction wheels -- devices that help orient the spacecraft -- are no longer operating, control of the trajectory has been impacted “by unpredictable acceleration,” Kawaguchi informed, "and the guidance and navigation is difficult now.” Nevertheless, he said, “we will try to have touching-down and sampling soon.”

The first landing and sampling, which could be as early as Saturday, will take place in a kind of dust pond the team has dubbed MUSES Sea (after "MUSES-C," the original, generic name of Hayabusa), one of the flatter areas on the rock and boulder-strewn asteroid. It is at that time that the target marker containing approximately 880,000 names gathered by The Planetary Society of Japan in 2002 will be released, hopefully to become at one with Itokawa for eons to come.

"The loss of Minerva is a disappointment, but it in no way diminishes the admirable mission that JAXA/ISAS has carried out," said Planetary Society Executive Director Louis D. Friedman.  "They are doing something that no one else has tried in space; and the achievements of rendezvous engineering and close up science are already truly remarkable."

If all goes as planned, or at least as well overall as it has gone so far, Hayabusa will successfully collect at least one sample and head for home in December. The return capsule is slated to parachute to a landing in the Australian outback in June 2007.