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.

Hayabusa on Itokawa

A depiction of Hayabusa's touchdown on the asteroid 25143 Itokawa in November 2005.

Akihiro Ikeshita / JAXA

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 900 miles per hour (400 m per second) over the past year and nudged it onto a trajectory that will pass within several thousand miles of Earth. "What is left is a series of trajectory corrections," Kawaguchi explains, "and the project team is finalizing the preparations for them."

Hayabusa's trajectory

A continuous, yearlong push from Hayabusa's remaining ion engine has nudged the spacecraft close to the desired encounter path (red line) that will permit the return of its sample-return capsule. Colored tracks correspond to the dates (month, day) at upper right. The engine was shut down on March 27th.


Barring an 11th-hour setback, in mid-June a small, 38-pound (17-kg) descent capsule will separate from the main spacecraft and slam into the atmosphere over south-central Australia. The larger craft will then maneuver to avoid Earth. Streaking through the darkness at 7.6 miles (12.2 km) per second, the capsule should parachute to the ground somewhere along a target zone, measuring 60 by 10 miles (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 16-inch-wide (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.

Hayabusa's return

Hayabusa's sample-return capsule slams into the atmosphere In the predawn darkness over south-central Australia in this artwork from the Japan Aerospace Exploration Agency.


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 reentry itself. The capsule should create an artificial fireball beginning at an altitude of about 120 miles (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 (SETI Institute) has been organizing an international team to observe the capsule's arrival from a 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!


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Bob Norton

April 2, 2010 at 10:59 am

Is it REALLY necessary for S&T to keep using archaic English measurement units only used by the most uneducated people of only TWO nations? I think that all of S&T's readers are intellectually adept enough to handle measurements presented ONLY in the Metric system. Please don't insult our intelligence by using feet, inches and miles.

Thank You

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Gene A, Dees

April 2, 2010 at 2:00 pm

I don't care if the measurement in the story are in Leagues per Fortnight ... just continue covering these stories. The "regular" media has passed them by completely and even more so now that Obama has pretty much quit space also pretty much completely. At least we get to read about a country's program that hasn't been knifed in the back. Never mind griping about the measurement ubits ... maybe these stories should be published only in the language of the country of origin ... and we all should now learn Japanese, Chinese, Russian, German and French.

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Jim Curry

April 3, 2010 at 4:57 am

Keep 'em coming, Kelly. I read your articles every week. Great links, too.

As to measurements, yes please keep using the archaic ones, and keep using the archaic language, English, also please. No doubt the progressives sneer at the use of BC and AD, too, prefering a more modern CE. Ignores the fact there wouldn't be a CE without an AD.

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[email protected]

April 3, 2010 at 9:27 am

Thanks Kelly, for the interesting update on Hayabusa, and also for including all the measurements in metric units. Too many American magazines fail to do that, even when writing about science and technology. Allow me to say that is a pleasure to read the articles of a columnist who covers international space science so well, and who clearly is aware that he has international readers 🙂

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