Hayabusa

Hayabusa, originally designated MUSES-C, was a robotic probe built by the Japan Aerospace Exploration Agency (JAXA). Its mission was to collect a sample from the near-Earth asteroid 25143 Itokawa and bring it back to Earth for study. Launched on 9 May 2003, it reached the asteroid in mid-September 2005. Once there, it examined the asteroid’s shape, rotation, surface features, color, composition, density, and history. In November 2005, it touched down on the asteroid and gathered tiny grains of material. These samples were returned to Earth inside the spacecraft on 13 June 2010. The probe also carried a small detachable lander named MINERVA, but that lander failed to reach the surface.

The mission achieved several firsts. While NASA’s Galileo and NEAR Shoemaker had previously visited asteroids, Hayabusa was the first to bring an asteroid sample back to Earth. It was also the first spacecraft designed from the start to deliberately land on an asteroid and then lift off again. (NEAR Shoemaker had made a controlled descent to the surface of 433 Eros in 2000, but it was not built as a lander and was deactivated after arrival.) Technically, Hayabusa was not meant to fully land; it was intended to briefly touch the surface with its sample collector and then move away. However, during the actual operation, it ended up sitting on the asteroid for about 30 minutes. Junichiro Kawaguchi of the Institute of Space and Astronautical Science led the mission.

The spacecraft launched on 9 May 2003 at 04:29:25 UTC aboard an M-V rocket from the Uchinoura Space Center (then called Kagoshima Space Center). After launch, its name changed from MUSES-C to Hayabusa, the Japanese word for falcon. Its four xenon ion engines operated nearly continuously for two years, slowly guiding it to its September 2005 rendezvous with Itokawa. Instead of entering orbit, the probe remained in a nearby station-keeping heliocentric orbit. It first surveyed the asteroid from about 20 km away (the “gate position”), then moved closer to a “home position,” and finally approached the surface for soft landings and sample collection. Because of the long communication delay, autonomous optical navigation was used extensively. When the collection horn touched down, the spacecraft fired tiny projectiles at the surface and captured the resulting spray. Some specks were collected for return.

After several months near the asteroid, the spacecraft was scheduled to fire its engines for the return trip, but this was delayed by attitude control and thruster problems. Once on its return trajectory, the re-entry capsule separated from the main craft three hours before reentry. It followed a ballistic path, entering Earth’s atmosphere at 13:51 UTC on 13 June 2010. The capsule experienced a peak deceleration of about 25 G and heating rates roughly 30 times those of the Apollo spacecraft. It landed by parachute near Woomera, Australia.

Before launch, JAXA defined success criteria and scores for major milestones. The primary objective was the world’s first implementation of microwave discharge ion engines, so operating those engines for more than 1,000 hours earned a full score of 100 points. Other milestones were built on that achievement.

The MINERVA mini-lander weighed only 591 grams and measured about 10 cm tall by 12 cm in diameter. It was designed to hop across Itokawa’s surface using an internal flywheel, taking advantage of the asteroid’s low gravity, and relay images to Hayabusa when in sight. It was deployed on 12 November 2005. The release command came from Earth, but before it arrived, Hayabusa’s altimeter measured a distance of 44 meters from the asteroid and triggered an automatic altitude-keeping sequence. As a result, MINERVA was released while the probe was ascending and at a higher altitude than intended, causing it to escape the asteroid’s gravity and tumble into space. Had it succeeded, it would have been the first hopping space rover. The Soviet Phobos 2 mission had also failed while attempting to deploy a hopping rover.

The mission’s scientific and engineering importance lies in how it improved understanding of asteroids. Scientists rely heavily on meteorite samples, but matching those samples to specific asteroids is very difficult.