A powerful robotic lunar scout, NASA's first in more than a decade, arrived at the moon early Tuesday on a mission to seek out potential landing sites and hidden water ice for future astronauts.

NASA's Lunar Reconnaissance Orbiter (LRO) fired its thrusters at 5:47 a.m. EDT (0947 GMT) in a 40-minute maneuver to begin orbiting the moon. It is NASA's first unmanned moon shot since 1998.

"We are in lunar orbit," said LRO project scientist Richard Vondrak at NASA's Goddard Space Flight Center in Greenbelt, Md. "We're not going past the moon. We're there to stay."

About the size of a Mini Cooper car, the $504 million LRO probe launched toward the moon on June 18 and spent four days in transit - about a day longer than astronauts on the Apollo missions in the late 1960s and early 1970s. The robotic probe is expected to spent at least one year mapping the moon for future manned missions, as well as several more years conducting science surveys.

"LRO has returned NASA to the moon," a flight controller said as NASA's LRO mission control center erupted in applause. The probe's lunar arrival comes just under one month ahead of the 40th anniversary of NASA's first moon landing by Apollo 11 astronauts on July 20, 1969.

The spacecraft carries seven instruments to map the moon in unprecedented detail, seek out water ice hidden in the permanent shadows of craters at the lunar south pole, and measure the temperature and radiation hazards future astronauts may face. The names of 1.6 million people are also riding aboard LRO as part of a public outreach program.

LRO is currently circling the moon in an extremely elliptical orbit that brings the nearly 2-ton probe within about 124 miles (200 km) of the lunar surface at its closest and reaches out to 1,863 miles (3,000 km).

"It went like clockwork," said Craig Tooley, NASA's LRO project manager. "In the end, it went exactly as planned."

Over the next few days, more thruster firings should fine-tine the spacecraft's flight path until it reaches its planned observation orbit of between 31 and 135 miles (50 to 218 km). Two of LRO's seven instruments, a pair of radiation sensors, scanned the space environment between the Earth and the moon, with the remaining five instruments to be activated in the next few weeks.

The first images from the powerful camera aboard LRO should be beamed back to Earth in the next few weeks, mission managers said.

"This whole new moon we're ready to see is out there waiting, and this mission is going to go get it," said Jim Garvin, NASA's chief scientist at Goddard.

A second unmanned spacecraft, the $79 million Lunar Crater Observation and Sensing Satellite (LCROSS), also launched with LRO and is expected to slingshot past the moon later today at about 8:20 a.m. EDT (1220 GMT). The spacecraft and an attached empty Centaur rocket stage will fly by the moon and shift into a polar orbit that will ultimately end in an Oct. 9 crash into a shadowed crater at the moon's south pole to probe for hidden water ice.

NASA plans to release live video from LCROSS as it flies past the moon at a distance of about 5,592 miles (9,000 km), mission managers have said.

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