In the early 2000s Japan was one of the largest economies in the world not to have a dedicated space agency, lagging behind even its fierce rival China. Despite a variety of missions in the 20th Century, the space industry in Japan was something that was yet to receive much public interest.
But when Japan announced that in 2002 it would attempt to become the first nation to return a sample from the surface of an asteroid, the public was instantly hooked. Here was something that they could be genuinely excited about, something that would put Japan firmly on the radar in the space industry. The revolutionary spacecraft for this mission would be called Hayabusa (originally MUSES-C), and aside from landing on an asteroid it would demonstrate the uses of ion drives. From the initial target launch date to the return home seven years later, however, this would be a mission dogged by problems.
On 9 May 2003 Hayabusa, which translates as ‘Peregrine Falcon’, lifted off from the Uchinoura Space Center in Japan. Five months after the launch in October 2003, Japan’s three separate space agencies merged into a single one: the Japanese Aerospace Exploration Agency (JAXA). The country now had its dedicated space agency; all it needed next was a successful mission.
Four xenon ion engines would take the spacecraft on a two-and-a-half year journey to the vicinity of Itokawa in June 2005. Hayabusa would remain in a heliocentric orbit (one around the Sun), similar to Itokawa’s, in order to approach the asteroid relatively slowly. But just several months after launching, the first disaster struck. The Sun unleashed a huge solar flare that bathed Hayabusa in solar radiation, crippling the cells on its solar panels and depriving the ion engines of full power. This would delay Hayabusa’s rendezvous with Itokawa by several months.
By the time Hayabusa was settled in position near Itokawa in September 2005, maintaining a distance of 20 kilometres (12.4 miles) from the asteroid, it was looking worse for wear. Not only were its ion engines subdued, but it had also lost functionality in two of its three reaction wheels that were used to rotate the spacecraft, relying instead on two chemical thrusters. But now the true science of the mission could begin; Hayabusa began surveying Itokawa, mapping the surface and analysing the characteristics of the asteroid.
Hayabusa was then instructed to practice landing on the asteroid but, after a botched first attempt, the second dry run on 12 November 2005 would prove disastrous. Hayabusa carried with it a small solar-powered lander called Minerva, weighing just over half a kilogram, which was designed to take advantage of Itokawa’s low gravity and ‘hop’ across the surface. A communications error, however, saw Hayabusa release Minerva at too high an altitude and it drifted off into space, never to be heard from again.
It was yet another setback for the now seemingly ill-fated Hayabusa but JAXA pushed ahead. A week later they attempted to land for real. On 19 November Hayabusa began its descent towards Itokawa at less than 12 centimetres (4.7 inches) per second until, 17 metres (55.8 feet) up, the unthinkable happened: contact was lost. It’s not clear what happened next, but it’s thought that Hayabusa “bounced” twice off the surface before coming to rest on the asteroid. It should have fired two bullets into the ground, which would have kicked dust up into its sample collector, but these failed to deploy. After half an hour Hayabusa left the surface, the first controlled landing and ascent from any other Solar System body except the Moon.
On 25 November it reached the surface again, but it’s not clear if the bullets worked here either. However, just by hovering and touching the surface engineers were convinced that dust from the asteroid would have been kicked up into the sample collector, and they made the decision to return home. They would not know until the collector was retrieved on Earth whether Hayabusa had been successful or not in getting a sample, but it was a risk they would have to take.
Things went from bad to worse on 9 December. JAXA lost communication with the spacecraft for a month when a thruster leak altered the direction that Hayabusa’s antenna was pointing. The fuel leak also meant the chemical thrusters, which had been used to orientate the spacecraft, were now no longer usable. Hayabusa could pitch and yaw with its ion engines and reaction wheel respectively, but it needed to be able to roll. JAXA’s engineers came up with an ingenious solution, using the tiny force of the Sun’s photon pressure on the solar panels to roll the spacecraft. Hayabusa could now begin the journey back to Earth.
With just two of its four ion engines operational, Hayabusa began limping home in February 2007 and, on 13 June 2010, it re-entered our atmosphere. The main spacecraft burned up as planned, with the sample capsule separating and parachuting safely to Earth in South Australia. On 16 Novemeber 2010 it was confirmed that the sample, weighing less than a gram, originated from Itokawa. Japan had successfully become the first nation to return a sample from the surface of an asteroid, thanks to a little spacecraft and a dedicated team that never gave up.
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Image credits: JAXA, NASA, Ed Schilling and Akihiro Ikeshita.