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Planetary News: Asteroids and Comets (2005)

Hayabusa: JAXA Regrouping for Touch-Down Landings on Asteroid

By A. J. S. Rayl
November 8, 2005
Hayabusa
Credit: JAXA

Engineers, scientists, and officials at the Japan Aerospace Exploration Agency (JAXA) spent the weekend pouring over data and regrouping after their asteroid chaser Hayabusa on Friday aborted the scheduled release of its lander to the surface of asteroid Itokawa. While the "abort" was a set-back, it was by no means the end of the mission.

Hayabusa will still go for the two touch-and-go landings to collect samples of the asteroid's surface materials slated for November 12 and November 25, Junichiro Kawaguchi, the mission's project manager, told The Planetary Society by email this weekend, but those dates may now change. Kawaguchi also said that they hope to release the lander, named Minerva, short for MIcro/Nano Experimental Robot Vehicle for Asteroid, during one of those descents.

Hayabusa – which means "falcon" in Japanese -- began its descent from a "hovering" position about 3 kilometers (almost 2 miles) from the asteroid in the early morning hours Japan Standard Time (JST) on November 4. The spacecraft was to have descended to just about 30 meters (100 feet) above the asteroid to test several instruments, and then move in closer to about 15 meters (50 feet) to release a target marker and then Minerva.

Since it takes around 17 minutes for a signal to reach Hayabusa from Earth, Hayabusa had been equipped with an autonomous navigation system; hence was carrying out commands on its own. The spacecraft descended slowly and smoothly over a period of several hours. Then, when it got to 700 meters (about 2,300 feet) from the asteroid "[t]he abort signal was issued," Kawaguchi said.  But Hayabusa "continued down a few hundreds meters [further] when it actually diverted" from descending any further, he said.

By Sunday, Hayabusa had flown up to an altitude of 9.6 kilometers (about 6 miles) from Itokawa and was then to travel back down its "home" position of about 7 kilometers (about 4.4 miles). The spacecraft is currently around 290,689,380 kilometers (about 180 million miles) from Earth.

South Pole of Itokawa
Click to enlarge >
South Pole of Itokawa
Hayabusa captured this image of the south pole of asteroid Itokawa in late October 2005. The smooth, partially shadowed area in the center is Muses Sea. Credit: JAXA

The team has not yet figured out exactly why the spacecraft aborted at the time it did, but they have an idea it's got something to do with the navigation camera. Hayabusa's navigation, guidance, and control system utilizes an Optical Navigation Camera (ONC), a Light Detection And Ranging (LIDAR), a Laser Range Finder (LRF), and Fan Beam Sensors (FBS). It is able to autonomously decide each move on its own by measuring the distance to and the shapes of the asteroid surface using the ONC and LIDAR. "How the spacecraft sees the terrain depends on where the camera is with respect to [the asteroid]," Kawaguchi said. "This may have caused the spacecraft [to be] at a loss for what the target direction [was]."

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. During the last two and a half years, Hayabusa has overcome a number of obstacles during its 1 billion-kilometer (621 million-mile) journey, including several life-threatening solar flares that slowed its arrival a bit. In the days and weeks to come it will be confronting its greatest challenges on the mission yet.