Atop an Atlas 5 rocket at Cape Canaveral Air Force Station in Florida sits the first step in what will surely be a long and arduous task for NASA—returning humans to the moon. The Lunar Reconnaissance Orbiter, or LRO, set to lift off this week, will orbit the moon in search of potential landing sites and useful resources, such as water ice, that would facilitate a long-term human presence.

For starters, LRO will improve maps of the moon, says astrophysicist John Keller of the NASA Goddard Space Flight Center in Greenbelt, Md., deputy project scientist for the $500-million mission. "A point I like to make about LRO," he says, "is that when it comes to the shape of the moon, we actually know the shape of Mars much better than we do of the moon." Three-dimensional laser-altimetry data taken by LRO will help to close that gap.

Planetary scientist David Kring, a senior staff scientist at the Lunar and Planetary Institute in Houston, sounds a similar tone, noting that the orbiter "will be exploring regions of the moon that have been fuzzy or completely invisible to us in the past."

The satellite's polar orbit will allow it to focus on especially desirable regions for human activities. At the moon's poles, Keller explains, the fairly consistent low angle of the sun makes available essentially constant access to solar power and, potentially, stores of water frozen in permanently shadowed craters. (A companion spacecraft to LRO will seek out direct evidence of that water ice in October.)

Among the orbiter's seven scientific instruments is one with a distinctly human-focused assignment: The Cosmic Ray Telescope for the Effects of Radiation (CRaTER). It will seek to characterize and assess the physiological effects of high-energy cosmic rays. Earth's inhabitants are largely protected from cosmic radiation by the planet's atmosphere and magnetic field, but long-term residents of the moon would be exposed to potential cellular and genetic damage without proper shielding.

CRaTER has cosmic-ray detectors separated by a material known as tissue-equivalent plastic. That plastic mimics how biological tissue absorbs radiation, and the LRO mission is the first time it will find use outside Earth's protective influence, Keller says. "By looking at the difference" between the radiation registered by the detectors, he explains, "you can say something about how much [energy] was deposited into that plastic."

The LRO mission springs from NASA's Vision for Space Exploration, the Bush-era plan to return humans to the moon by 2020 on board Ares rockets currently in development to replace the space shuttle, which retires next year. But while the lunar timeline and the Ares program are under scrutiny by a blue-ribbon panel of independent experts convened by the White House, the robotic precursor to human exploration continues apace.

Kring says that even given the uncertainties in the future of manned spaceflight in the U.S., the lunar orbiter is a mission whose time has come. "Not only is this the right time to launch LRO, the LRO spacecraft should be the first in a small fleet of missions that expand our horizons and, simultaneously, provide opportunities to enhance our nation's technological capabilities," he says.