Hayabusa Probe Nears Itokawa Asteroid

by Chris Bergin

A daring Japanese mission is on target to bring the first ever samples of an asteroid back to Earth and within the grasp of planetary scientists, available for first-hand analysis.

The Japanese Hayabusa probe, one of the most sophisticated to date, departed Earth in May 2003, embarking on a four and a half year mission to a nearby asteroid, on an ambitious mission to acquire and return samples of the object to Earth by the summer of 2007.

The target asteroid is 1998SF36, an S-type asteroid describing a near-circular Mars-crossing orbit around the sun. The object, measuring about 500 meters long and 200 meters wide, is actually composed of two asteroids joined together. Like other S-types, 1998SF36 is composed mainly of metals (such as nickel and iron silicates), making objects like it future targets for mineral prospectors.


About seventeen percent of the solar system’s asteroids are believed to be S-types.


By September 12, the 500 kg Hayabusa probe arrived at a distance of 20 km of 1998SF36, an occasion for renaming of the object Itokawa, in honor of Japanese rocket scientist Hideo Itokawa. Hayabusa has rightly become a source of pride for Japan’s space program.


Bruce Murray, a former JPL director and co-founder of the Planetary Society remarked, “From a technological point of view, [the Hayabusa mission] is a remarkable achievement, and one that every space faring nation admires. It is especially remarkable when you consider that Japan does not have the military aerospace infrastructure that the United States, Russia, and Europe have.”


The MUSES-C probe, christened Hayabusa following its launch into orbit two years ago, carries several breakthrough technologies into the solar system. The probe is propelled on its billion mile journey by an electrical ion engine, using xenon gas as fuel. Ion propulsion, already successfully tested aboard probes like the comet-chasing Deep Space One, is considered highly efficient for long-term long-distance missions.


Due to Hayabusa’s distance from Earth, several light-minutes away, real-time remote control from mission control is impractical. An Autonomous Navigation System will allow Hayabusa to study the asteroid’s surface, selecting a landing site on its own. The Optical Navigation Camera (ONC) will analyze the asteroid’s surface using a Light Detection and Ranging (LIDAR) and pick out features to be used as reference points as the probe touches down. At an altitude of 100 meters, the LIDAR system will shut off, and the Laser Range Finder (LRF) will activate, guiding Hayabusa to its landing. As Hayabusa nears the landing site, it will release a Target Marker on a tether that will touchdown on the surface, serving as a homing beacon for the probe on its final approach.


Hayabusa is a species of Japanese falcon, known for its ability to swoop swiftly down upon its prey and carry it off in its clutches. Such maneuvers will be required by the probe when acquiring samples of the asteroid.


Hayabusa will maneuver around Itokawa over a five month period, touching down twice, acquiring a sample at each landing site. Due to the asteroid’s light gravity, a hard landing will bounce the probe back into space. Hayabusa will swoop down onto the surface, grab a sample and gently lift off.


On its first touchdown, Hayabusa will release MINERVA, a robot that will hop and explore Itokawa’s surface during the length of the mission.  


Hayabusa will reenter Earth orbit by summer 2007. The module containing the two Itokawa samples will eject from the probe and touch down in the Australian outback.


Samples from asteroids are expected to reveal clues about the formation of the solar system that cannot be extracted from planets. Having undergone little change since the birth of the planets, asteroids are essentially geochemical time capsules that were sealed 4.5 billion years ago.

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