In general, good landing sites need to be level and free from large boulders that could damage or tip the spacecraft as it attempts to land. And it's up to LRO to make those landings as safe as possible.

Astronauts will want to avoid places with steep slopes that could tip the spacecraft, so LRO includes a laser ranging system that will build an elevation map to show the contours of the polar surface. The instrument, called the Lunar Orbiter Laser Altimeter (LOLA), records the time it takes for a laser pulse to travel from the spacecraft to the lunar surface and back to calculate the height of the lunar terrain. After a year in orbit aboard LRO, LOLA will have created an elevation map of the polar regions that is accurate to within a half-meter (20 inches) vertically and 50 meters (about 160 feet) horizontally.

LRO will also use data from another instrument that measures temperatures to double-check the safe zone map. Temperatures change more rapidly in areas with loose materials (lots of rocks). By analyzing how quickly temperatures change in potential landing zones, planners using the instrument, named Diviner, can rule out areas that appear smooth but actually are likely to be rocky.

LRO also carries a pair of eagle-eyed cameras, called the Narrow Angle Cameras (NACs) which together can take images that reveal details as small as a half-meter (almost 20 inches) over swaths 10 kilometers (about 6.2 miles) wide. As LRO orbits over the poles, the moon rotates beneath the spacecraft, and the NACs will gradually build up a detailed picture of the region. It will be used to identify safe landing zones free of large boulders and craters, allowing astronauts to avoid surprises like Apollo 11.

LRO is being assembled and managed by NASA Goddard, and is scheduled to be launched in early 2009. NASA plans to have astronauts back on the moon by 2020. As astronauts close in on a new landing site late in the next decade, they can thank NASA Goddard's small robot scout for showing the safest approach.