Five days before it will fall into the Australian outback, Japan's returning Hayabusa asteroid mission finished targeting the landing site Tuesday in a final planned ion engine burn.

Credit: JAXA

Hayabusa's ion engine fired for two-and-a-half hours yesterday to optimize its trajectory, ensuring the spacecraft releases a diminutive return capsule exactly on course for landing in the Woomera test range in South Australia.

The capsule is still expected to touch down under a parachute around 1400 GMT (10 a.m. EDT) Sunday. It will be just before midnight in Australia.

The Japan Aerospace Exploration Agency says Hayabusa is now traveling about 1.2 million miles from Earth, nearly five times the distance of the moon.

A previous trajectory correction burn ended Saturday to bend Hayabusa's future path from an imaginary point 200 kilometers, or 120 miles, above Earth toward Australia.

Tuesday's maneuver was likely the last time Hayabusa's ion propulsion system will be fired. The highly-efficient system, which consumes ionized xenon gas, has amassed 40,000 hours of operating time on four engines since the mission launched in May 2003.

The next milestone will be the release of the re-entry craft approximately three hours before landing. The jettison was rescheduled later in the flight due to concerns about the capsule's battery.

Hayabusa's $200 million mission was extended three years after a fuel leak threatened the spacecraft at the end of its visit to asteroid Itokawa, a potato-shaped rock about the size of a city block. Controllers lost contact with the probe and were not able to recover the craft in time to resume the trip home.

Artist's concept of Hayabusa's entry capsule returning to Earth under parachute. Credit: JAXA

"We want to heat it up and prevent it from becoming cold, we changed the separation time as late as possible to three hours before entry," said Junichiro Kawaguchi, Hayabusa's project manager.

The 16-inch-wide capsule will be spring-ejected from the Hayabusa mothership in a spinning motion for stability.

A carbon fiber heat shield will protect the craft during its 25,000 mph re-entry. Temperatures around the capsule should reach about 4,900 degrees Fahrenheit, according to JAXA.

The unprotected Hayabusa mothership will plummet into the atmosphere and burn up.

A NASA DC-8 tracking plane will fly under the capsule's re-entry trajectory to document the fiery return.