New Hope for Plucky Japanese Asteroid Mission

by Stephen Clark

Date: 21 November 2009 Time: 02:03 AM ET

Japanese engineers have devised a plan to combine parts from two partially-failed ion engines to resume the Hayabusa asteroid probe's journey back to Earth.

In a press release Thursday, officials said they will use the neutralizer of Thruster A and the ion source of Thruster B to provide enough power to guide the 950-pound spacecraft home next June.

Hayabusa launched in 2003 with four ion engines. Thruster A was shut down due to instability shortly after launch, while Thruster B was turned off after high voltage in its neutralization system.

Thruster C was manually switched off after signs it might be damaged by high electrical currents, and Thruster D failed two weeks ago due to a voltage spike.

The Nov. 4 glitch left Hayabusa without a propulsion system and put its scheduled return to Earth in serious doubt. But the new plan gives Japanese officials new hope.

"While the operation still needs monitored carefully, the project team has concluded the spacecraft can maintain the current return cruise schedule back to the Earth around June of 2010, if the new engines configuration continues to work as planned," the Japan Aerospace Exploration Agency said in a statement.

Hayabusa's four experimental microwave discharge ion engines consume xenon gas and expel the ionized propellant at high speeds to produce thrust. Ion engines are more efficient than conventional chemical thrusters because they use less fuel and can operate continuously for thousands of hours.

The craft's thrusters have accumulated almost 40,000 hours of burn time since the probe launched.

Plans call for the spacecraft to continue thrusting until March, when it will shut down the ion system and coast toward Earth for a parachuted landing in Australia.

Hayabusa spent three months exploring asteroid Itokawa in late 2005. The probe took 1,600 pictures and collected about 120,000 pieces of near-infrared spectral data and 15,000 data points with its X-ray spectrometer to investigate the small potato-shaped asteroid's surface composition.

The spacecraft approached Itokawa several times, attempting to fire a pellet into the asteroid's surface and retrieve rock samples through a funnel leading to a collection chamber.

During a failed sampling attempt in November 2005, Hayabusa made an unplanned landing and spent up to a half-hour on Itokawa, becoming the first spacecraft to take off from an asteroid.

Although telemetry showed Hayabusa likely did not fire its projectile while on the surface, scientists were hopeful bits of dust or pebbles found their way through the funnel and into the sample retrieval system.

Hayabusa was later stymied by a fuel leak and ground controllers temporarily lost communications with the spacecraft, which is about the size of an average refrigerator.

Controllers labored to overcome the issues, which were compounded by the loss of two orientation-controlling reaction wheels and power cells in an electrical battery.

The craft's departure from Itokawa was delayed a year because of the problems, postponing its return to Earth from 2007 until 2010.

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