Japan's Kaguya probe slid into lunar orbit late Wednesday after a circuitous 20-day trek from Earth to begin more than a dozen science investigations designed to gain insights about the moon's history.

Credit: JAXA

The two-ton spacecraft fired its maneuvering thruster for between 10 and 20 minutes at about 2055 GMT (4:55 p.m. EDT) Wednesday, or in the predawn hours Thursday Japanese time, according to JAXA spokesperson Satoki Kurokawa.

"We have completely done it and found no problem," Kurokawa said.

Kaguya entered an egg-shaped polar orbit circling the moon at distances ranging from 63 miles up to about 7,296 miles, according to a JAXA statement issued Thursday night.

Subsequent maneuvers are planned over the next two weeks before the spacecraft arrives in a circular orbit with an altitude of about 60 miles. Two small 110-pound satellites will be released from Kaguya at different points in the altitude reduction maneuvers.

Called RSAT and VRAD, the satellites will help the main Kaguya orbiter study the weak gravity field on the moon's far side and probe the tenuous lunar ionosphere by observing interference of radio signals.

RSAT will be released Oct. 9 in an orbit with a high point of 1,500 miles, while VRAD is set for an Oct. 12 deployment in an orbit stretching up to 500 miles from the moon.

Kaguya is scheduled to complete the engine firings by Oct. 19.

After several more weeks of instrument checkouts, the ten-month observation phase of the mission will begin in December. A mission extension is likely if Kaguya's systems are in good health late next year, according to JAXA officials.

The $480 million mission began with a fiery Sept. 14 liftoff from Japan's primary launch site on Tanegashima Island. The pickup truck-sized probe - also known as SELENE - was deployed from the H-2A rocket about 45 minutes later. See our launch story.

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On-board engines conducted a series of firings to gradually raise the craft's orbit before eventually sending Kaguya on an arcing trajectory to intercept the moon. The final burn before arriving at the moon occurred on Saturday to boost Kaguya's orbit high enough for the probe to be grasped by the moon's gravity.

The mission includes the first high-definition television camera ever carried to deep space, and the 36-pound camera already beamed back stunning images of Earth Saturday from a distance of nearly 70,000 miles.

More videos are expected throughout the mission, including spectacular footage of Earth rising above the lunar horizon. Kurokawa said imagery of the moon from the high-definition camera is expected sometime in December.

The camera was provided to the mission by Japanese broadcasting giant NHK.

The mission features a total of 15 instruments to survey the moon to help chart its history and evolution. The payload will map the surface, look for evidence of ice trapped in cold spots near the lunar poles, and study the environment in space around the moon.

Kaguya will measure chemical abundances on the moon, and a radar sounder on the probe will pierce the lunar surface to chart underground structures to a depth of several miles.

Spectral instruments on the spacecraft will search for traces of hydrogen near the lunar poles. Hydrogen is often a signature for the signature for water, and scientists believe deep craters near the moon's poles could harbor water ice because they never see sunlight.

A sensor at the tip of a 39-foot-long boom will gather data on the moon's feeble magnetic field. Other space environment payloads included aboard Kaguya will study the solar wind and lunar ionosphere.

Information on the lunar radiation environment will prove valuable in planning future human voyages to the moon, according to JAXA scientists.