The incredible story of the first mission to mine an asteroid

How the Japanese mission that seemed destined to fail returned the first asteroid samples to Earth.

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The Hayabusa probe, built by the Japanese Aerospace Exploration Agency (JAXA), was launched on a Japanese M-V rocket on 9 May 2003 from the Uchinoura Space Centre in Japan. Its mission was to become the first man-made object to return samples from an asteroid – in this case Itokawa, an S-Type asteroid chosen for its occasional proximity to Earth and its interesting iron and magnesium-silicate surface.

To obtain the necessary speed to reach Itokawa 186 million miles (300 million km) away, Hayabusa used its ion and chemical engines to orbit the Sun for more than a year. This provided continual acceleration, and when it finally approached Earth again it performed a swing-by to propel itself towards the Itokawa asteroid two years after its launch.

Communication to and from Hayabusa at the asteroid took 40 minutes, so it had to finish most of its mission alone. Upon its approach it dropped a 10cm-wide sphere with a reflective surface onto Itokawa. By shining light onto the sphere, Hayabusa could calculate its distance to the ground.

The probe was supposed to drop a lander, named Minerva, onto the surface. However, the lander missed the surface, and JAXA instead decided to land Hayabusa directly on the asteroid. Attempts to fire a ball bearing into the ground to kick up dust were unsuccessful, but fortunately the power of its engines disturbed enough dust to be collected inside a capsule.

After leaving the asteroid it lost all propulsion barring two ion engines, in addition to experiencing a communications failure with mission controllers. However, thanks to some clever workarounds including the use of the Sun’s pressure against the solar panels to help steer the spacecraft, Hayabusa eventually limped home three years behind schedule.

Upon arrival at Earth the capsule containing the sample from Itokawa separated from the probe, with the latter burning up as planned in the atmosphere and the former landing safely in Australia on 13 June 2010. However, all was not over just yet. JAXA were still unsure if Hayabusa had successfully retrieved samples or not. It was not confirmed until several months later that the particles in the sample container were from Itokawa, bringing to an end a remarkable mission that had been so close to failure but eventually came up trumps with the sample JAXA were looking for.

Image courtesy of JAXA and Akihiro Ikeshita.

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