Taken from a NASA aircraft, this video still shows the breakup of the probe , note the tiny dot at lower right. This is the capsule hopefully carrying precious samples from the asteroid. (Image credit: NASA)

The team at the Japanese Aerospace Exploration Agency deserve congratulations for the amazing (and hopefully record-breaking) Hayabusa mission to asteroid 25143 Itokawa. Launched in 2003 (the spacecraft was called MUSES-C at launch, but was renamed in flight), this mission has battled against an extraordinary run of bad luck and technical issues.

This was an extremely ambitious mission, even by ESA or NASA’s standards. Pushed gently across space by solar powered ion thrusters, Hayabusa experienced high radiation from an unexpected solar flare. This ordeal damaged its solar panels, reducing their efficiency and therefore the ion drive’s thrust. As a result, Haybusa rendezvoused with Itokawa in September 2005, about three months later than planned. Colour images from the probe showed a grey, rubble-strewn surface devoid of impact craters. Hayabusa released a tiny robot lander called MINERVA which would have bounced over the 500 m long asteroid’s surface taking images, but alas a technical error sent the teapot-sized robot tumbling into space. After observing the asteroid from 2okm above, Hayabusa descended to a gentle touchdown on the surface before rising away. This exercise was repeated and the probe attempted to collect some samples of the surface material. The sampling mechanism failed to work as planned but there is a good chance some particles of asteroidal material were collected.

Meanwhile, two of Hayabusa’s reaction wheels, devices used to point it in space, failed and instead propellant had to expended to manoeuvre it instead. Fuel leaked from a faulty pipe, contact between Earth and the probe was lost several times but recovered and the craft suffered a frustrating list of further glitches, but the controllers fought hard to retrieve the mission, which has been described as “the Apollo 13 of unmanned spaceflight”.

On the evening of 13 June 2010, Hayabusa returned home as planned after seven years of wandering through the Solar System. The 380 kg probes made a spectacular deathdive into our atmosphere, breaking into incandescent fragments over Australia, releasing a capsule hoped to carrying precious samples from the asteroid. It parachuted to the desert below and was recovered the next day. The capsule is still being examined to see if we have bits of Itokawa on Earth.

Asteroids, often overlooked, are fascinating objects. Learning about them has so much to teach us about the history of the Solar System (plus I would venture to suggest that one day they may be of vast economic importance). Hayabusa’s epic odyssey will supply raw research material for decades to come.

Further reading

JAXA’s official Hayabusa page is here and I cannot recommend too highly the coverage of the mission by both the BBC’s Jonathon Amos at his blog and Emily Lakdawalla at the Planetary Society Blog (it you would like your own Hayabusa, Emily descibes how to knit one here!). You can read about NASA’s Dawn mission to the asteroids here.


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