To The Moon, Alice

After a successful blast-off from Cape Canaveral on June 18, two space probes are on their way to the moon on a scouting expedition for future human exploration.

Thunderstorms and lightening had threatened to scrub the launch of the National Aeronautics and Space Administration's Lunar Reconnaissance Orbiter (LRO) and Lunar Crater Observation and Sensing Satellite (LCROSS). But 17 minutes before Thursday's third launch opportunity, engineers gave the go-ahead.

The two spacecraft, carried aloft together on one rocket, have different objectives. LRO, which NASA is billing as "leading the way back to the moon," will arrive at the moon on June 22. After about two months settling into orbit, the craft will begin mapping the lunar surface, examining potential landing sites.

Meanwhile, LCROSS is on a suicide mission to search for water ice in the moon's perennially shadowed polar areas. In October, LCROSS will eject the spent second stage of the launch rocket, which will crash onto the surface, throwing up tons of debris. LCROSS and LRO instruments will look for water in the ejected material, said Jay Jenkins, program executive at NASA headquarters in Washington, D.C. Then the LCROSS craft itself will crash to the surface, throwing up another plume also to be analyzed.

The two missions, which cost about $600 million, are the first of a series of projects under NASA's Vision for Space Exploration. The program was enacted by the Bush Administration in 2004 to further human exploration of the moon and Mars.