Japan’s Hayabusa probe, potentially loaded with the first rock samples from an asteroid, fired up one of its ion engines Wednesday to begin the second phase of the explorer’s return voyage to Earth.
Hayabusa ignited a single ion engine at 0235 GMT Wednesday to begin pulsing for up to 8,000 hours to finish guiding the spacecraft toward Earth, according to the Japan Aerospace Exploration Agency, or JAXA.
The spacecraft’s ion propulsion system has already completed than 31,000 hours of operations since its launch in 2003.
The probe carries four ion engines, but engineers believe some of the devices are not capable of long-duration firings. Officials designed a taxing return trajectory using a single engine to reduce the odds of a major failure.
Despite the hard work of several dozen engineers, Hayabusa still faces more hurdles before making its scheduled parachuted landing in Australia in June 2010.
“We are not so optimistic, but not so pessimistic,” said Makoto Yoshikawa, Hayabusa project scientist.
Officials said the ion engine must accelerate Hayabusa by nearly 900 mph by March 2010, when engineers will turn off the machine to begin the probe’s final approach to Earth.
“If the current status of Hayabusa (remains) until the final stage, we are sure that it will come back to the Earth,” Yoshikawa said.
The spacecraft still has enough xenon gas to power the ion engine and control its orientation in space, according to JAXA.
“We are continuing to pay careful attention to our onboard equipment and are doing our utmost to operate the Hayabusa with the greatest care,” officials said in a statement.
The craft’s ion engines use microwave discharge to ionize xenon gas and accelerate the plasma to high speeds. The highly-efficient engines produce little thrust, but the devices can operate for months to propel the spacecraft across the solar system using small amounts of fuel.
Hayabusa completed the first round of return trip ion engine operations in October 2007 after a burn lasting about four months.
The mission’s ground team refined operations plans since 2007 to increase the odds of Hayabusa’s successful return, according to Yoshikawa.
Scientists also devised methods to find Hayabusa’s entry capsule after landing and created plans to transport the sample canister from Australia to a specially-outfitted science lab in Japan, Yoshikawa said.
The science team is currently testing the mission’s curation facility and discussing how to analyze asteroid samples returned by Hayabusa.
But officials still are not sure if the 950-pound probe is actually carrying the priceless samples.
Hayabusa spent three months near asteroid Itokawa in late 2005, studying the space rock and attempting a series of close approaches to collect bits of rock and dirt.
A pellet was supposed to be fired into the surface of Itokawa to force the rocks through a funnel to guide the precious samples into a container for the voyage back to Earth.
Those plans did not materialize in November 2005 and Hayabusa spent up to 30 minutes on the asteroid’s surface during a failed retrieval attempt. Officials later reviewed telemetry data from a subsequent attempt and determined the pellet likely did not fire because the system was disarmed.
Scientists hope some particles were funneled into the collection chamber, even if the pellet did not fire as planned.
Engineers were forced to postpone the start of Hayabusa’s return trip by a year after the mission was struck by a fuel leak and communications problems.
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.
Stephen Clark
Spaceflight Now
