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Japanese lunar orbiter headed for a crash landing

Posted: June 9, 2009

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Japan's $500 million Kaguya moon mission will end with a suicidal plunge into the lunar surface Wednesday, an impact that may be visible through large telescopes in Asia and Australia.

An artist's concept of Kaguya. Credit: JAXA
The violent demise was orchestrated by ground controllers to dispose of the spacecraft before it runs out of fuel.

Officials at the Japan Aerospace Exploration Agency estimate the Kaguya probe will impact the moon at about 1830 GMT (2:30 p.m. EDT) Wednesday, or about 3:30 a.m. Japanese time Thursday.

Kaguya will fire its engine for the last time at about 1740 GMT, slowing the probe's velocity by about 6 mph to target a location in the moon's southern hemisphere. The expected impact site is near a feature called Gill Crater positioned near the lower right corner of the moon's near side as viewed from Earth, according to JAXA.

The site will be in darkness near the terminator at the predicted time of impact.

The moon will be visible from much of Asia and Australia as Kaguya hits the surface. There is a chance the flash of the impact could be observed through large telescopes in those regions, according to Shin-ichi Sobue, a member of the mission's operations team.

"The Japanese public wishes to see the Kaguya impact from observatories," he said.

Scientists will also look for material launched high above the surface by the collision.

A similar impact in 2006 by Europe's SMART 1 satellite was detected by the Canada-France-Hawaii Telescope. Astronomers there observed the flash of the impact and the resulting dust cloud.

Kaguya, which is about the size of a sports utility vehicle, is currently circling the moon in a ground-hugging orbit that takes the spacecraft within about 10 miles of the surface during each circuit.

Two previous burns lowered the spacecraft's orbit from its operational altitude of about 60 miles.

Engineers expect the probe will hit the moon at a low angle as it speeds horizontally at about 4,000 miles per hour. The low angle means Kaguya's vertical speed is much lower, causing it to carve out a small crater and only excavate a modest amount of ejecta, the bits of rock and dust thrown above the surface by impacts.

Kaguya, also named SELENE, launched in September 2007 and arrived at the moon about 20 days later to begin nearly two years of observations using 15 science payloads.

The instruments included a stereo camera suite, an array of sensors designed to sniff for hydrogen, a laser altimeter that measured the shape of the moon, and a payload to probe the local radiation environment.

Kaguya also carried a high definition camera that beamed back stunning video imagery of the moon.

The spacecraft released two daughter satellites after entering lunar orbit. The 110-pound satellites helped Kaguya study the moon's gravity field and the lunar ionosphere. One of the probes was guided into the moon in February, while the other is still being operated.

The mission was part of a flotilla of Asian robotic lunar explorers launched during the last two years.

China's Chang'e 1 orbiter also launched in 2007 and ended its mission in March with a similar commanded destruction.

India launched the Chandrayaan 1 probe last October and it continues to operate in lunar orbit.

NASA plans to launch the Lunar Reconnaissance Orbiter next week to begin mapping the moon in a search for potential landing sites for piloted missions late in the next decade.