Hayabusa’s sample-return capsule will slam into the atmosphere in the predawn darkness over south-central Australia in June (Illustration: JAXA)

It seems years ago – November 29, 2005, to be exact – since a Japanese spacecraft named Hayabusa touched down on a small asteroid in the hope of grabbing samples of its dusty surface and returning them to Earth. Had the mission gone according to plan, the precious bits from asteroid 25143 Itokawa would have reached waiting scientists in June 2007.

But the flight of Hayabusa, Japanese for “falcon,” has been anything but nominal. In fact, it’s been more of a train wreck.

The craft was nearly lost during its grab-and-go encounter due to a series of malfunctions that should have doomed the spacecraft. But it hung on, despite suffering a massive fuel leak, battery failure, and being incommunicado for two months. Then its attitude-control system failed. The loss of three of its four xenon-powered engines meant it would take three extra years to get the crippled craft home, nursed every step of the way by its dedicated team of engineers.

Well, folks, Hayabusa is almost home. Late word from project manager Jun’ichiro Kawaguchi is that the sole remaining engine was commanded to shut down on March 27th, having gently accelerated the craft by 400 metres per second over the past year and nudged it onto a trajectory that will pass within several thousand kilometres of Earth. “What is left is a series of trajectory corrections,” Kawaguchi explains, “and the project team is finalizing the preparations for them.”


Unknown cargo

Barring an eleventh-hour setback, in mid-June a small 18-kilogram descent capsule will separate from the main spacecraft and slam into the atmosphere over south-central Australia. The larger craft will then manoeuvre to avoid Earth. Streaking through the darkness at 12.2 kilometres per second, the capsule should parachute to the ground somewhere along a target zone, measuring 100 by 15 km, in the remote Woomera Test Range.

After whisking it back to a clean room at the Japan Aerospace Exploration Agency (JAXA), scientists will carefully open the 40-cm capsule to learn, finally, whether it contains any asteroidal bits. It’s hardly a sure thing – despite sitting on Itokawa’s surface for 30 minutes, Hayabusa failed to fire two small tantalum pellets designed to kick surface material into a collection cone.

Hayabusa’s successful return would be a big deal in Japan, and plans for the welcome-home party are well under way. Kawaguchi has been careful not to divulge the exact date publicly, pending the engine shutdown and a sign-off from Australian authorities. “It is not at the beginning of June, and it is not at the end of June,” he teases. JAXA has produced an informative 21-minute video about the mission, in English, that you can view here. There’s even a dramatic movie treatment: Hayabusa: Back to the Earth.

Airborne observatory

Because spacecraft rarely come down through the atmosphere so fast – Earth-orbiting satellites fall in about a third slower – there’s plenty of scientific interest in the re-entry itself. The capsule should create an artificial fireball beginning at an altitude of about 200 km and hit a peak brightness of magnitude -6.7 (several times brighter than Venus) before deploying its parachute.

For the past year, meteor specialist Peter Jenniskens of the SETI Institute in California has been organising an international team to observe the capsule’s arrival from an instrument-packed DC-8 jet flying near the recovery zone. Jenniskens mounted a similar effort for the return of the Stardust sample capsule in January 2006.

Will Hayabusa, despite all its problems, make it back to Earth? Will the capsule contain hard-won bits of asteroid Itokawa? Will Kawaguchi and his team get a ticker-tape parade through downtown Tokyo? Stay tuned for the final chapter of this remarkable mission!

Courtesy of Sky and Telescope magazine