Japan shoots for a piece of an asteroid

The target
Hayabusa is aimed at a small piece of space debris once known as “Asteroid 1998 SF36” — signifying that it was discovered only a few years ago and was too small for anybody to bother to name. But once it had been selected as a sampling target, the International Astronomical Union acceded to Japan’s request to name it after Hideo Itokawa, the father of Japanese rocketry.

The potato-shaped asteroid measures about a quarter-mile (500 meters) wide, with a gravitational pull hardly more than a millionth of Earth’s. Itokawa's gravity is so faint that the probe won’t even bother to orbit the asteroid. Instead, it will hover about 12 miles (20 kilometers) away, surveying the surface both from the full sunlit side and then later from above the boundary between day and night.

Itokawa's shape and density are uncertain, and its 12-hour rotation period creates extra navigation hazards during the Hayabusa probe's slow approach.

After several weeks of surveying, the probe would begin its main task: retrieving about a gram (0.036 ounce) of dirt from up to three points on the surface, and then returning the samples to Earth two years later. The probe is too far away for real-time remote control from Earth, so to perform this delicate operation the probe has a sophisticated autopilot.

How it will be done
Using small liquid-fueled engines (rather than the low-thrust ion drive that serves during interplanetary cruising), Hayabusa will approach a pre-selected touchdown point. It will use a ranging laser to measure its approach range and speed, and half an hour before contact will deploy an optical sensor into the soil so that its camera system can sense any horizontal drift rates. The first sensor, about the size of a softball, will carry almost a million names of people who supported the project.

The probe will contact the surface with a large "collection horn," and then it almost immediately will fire a bullet into the dirt. Some of the material that scatters from the impact will make its way into a collection chamber, which will then be sealed. This process can occur up to three times at different locations.

Hayabusa will also deploy a small hopper robot named Minerva. This solar-powered mini-spacecraft will relay images from its three cameras to Hayabusa whenever the two vehicles are in direct line-of-sight contact.

Assuming the craft’s power system and four ion engines continue to function, the craft will return to Earth in July 2007. A special capsule will hit the atmosphere at 29,000 mph (13 kilometers per second), about the same speed as returning Apollo spacecraft, and undergo forces of about 25 G’s before touching down in central Australia.

The material will be brought to a new national laboratory in Japan. There it will be analyzed, and some of it will be shared with foreign investigators.

James Oberg, space analyst for NBC News, spent 22 years at the Johnson Space Center as a Mission Control operator and an orbital designer.

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