As Hayabusa returns to Earth, A Recap

The Planetary Society blog gives a recap of the Hayabusa mission, a few days before a retry capsule comes back to Earth...

Hayabusa was conceived as a daring mission that would return a sample from a tiny asteroid, smaller by far than any that had been visited before. The asteroid would be so small that its gravity would be negligible; instead of entering orbit, Hayabusa would match orbits with it and grab a sample in a maneuver that was more similar to docking with another spacecraft than it was to landing on another planet.

The audacious mission required incredibly precise guidance and control of the little spacecraft. The solar-powered craft was fitted with four gimbaled ion engines as its main thrust source, a more traditional chemical thruster system (actually, two separate systems for redundancy) for maneuvering (particularly important for the delicate operation of touching down on the asteroid), and three reaction wheels for control of the spacecraft's orientation in space. It had a sampling horn that would contact the asteroid, fire pellets at its surface to knock asteroid dust off, and enclose the flying asteroidal material into a sample return capsule equipped with heat shield and parachute.

The spacecraft launched as "MUSES-C" on May 9, 2003, aboard an MV-5 rocket, from the Uchinoura Launch Center, Kagoshima, Kyushu, Japan. After its launch, it was renamed "Hayabusa," or "peregrine falcon."

Hayabusa captured this photo of Itokawa as it passed between the Sun and the tiny asteroid on November 10, 2005. Hayabusa's shadow is visible on the surface of the asteroid -- a tiny spacecraft causing a tiny solar eclipse on a tiny object.

Hayabusa's near-Earth asteroid target was chosen not because of any particularly special qualities of the asteroid itself. Rather, the asteroid was picked on the basis of what Hayabusa could reach, given its launch date and the capabilities of its ion-powered flight. In fact, Hayabusa's eventual destination was only first discovered less than five years before the spacecraft launched toward it. (In this way, the Hayabusa mission is similar to the Kuiper belt mission of New Horizons -- that spacecraft will be aimed for some small Kuiper belt object or objects that still have yet to be discovered.)

Hayabusa's target asteroid had been named 1998 SF36 when it was discovered by the LINEAR project, and received the provisional designation 25143 shortly after. After Hayabusa launched, it was formally named Itokawa after Hideo Itokawa, who is regarded as the father of Japanese rocketry, and who oversaw the first orbital Japanese launch in 1970.

Link: Planetary Society Blog (Six days left for Hayabusa: A recap of the mission)