NASA's next lunar orbiter will launch later this year, the first step in an ambitious plan to return humans to the Moon--and send them on to Mars. The spacecraft, called the Lunar Reconnaissance Orbiter (LRO), will use new technology to make precise maps of the Moon's surface, to search for resources such as ice, and to assess the threat that radiation in the environment could pose for humans.

LRO is the most advanced lunar satellite NASA has built, says Richard Vondrak, the project scientist for LRO, who adds that it will provide information that would have been impossible to collect a few decades ago. "We are surveying the Moon in more detail than any other celestial body for the benefit of all countries, including China, Japan, and India, who have said they have ambitions to put people on the Moon in the next 10 to 20 years," adds David Smith, a NASA scientist working on LRO.

LRO is part of NASA's Vision for Space Exploration, a program intended to, among other things, answer fundamental questions of physics, search for extraterrestrial life, and seek new resources, such as power sources, for Earth. The program calls for humans to return to the Moon. But before that happens, says Vondrak, it's necessary to understand much more about the Moon's surface radiation and topography.

"During Apollo, there were a number of near-fatal mistakes," says Smith. "We did not land on a flat surface, and there were boulders everywhere, which could have damaged the vehicle and prevented a return to Earth. Safety standards today would not have allowed Apollo."

The Apollo manned-spacecraft program shut down in 1975, and it was not until the 1990s that the United States sent more satellites to orbit the Moon--Clementine and the Lunar Prospector, which spent months orbiting the Moon and sending back data. Clementine was a joint project between the U.S. Department of Defense and NASA that also tested new ballistic technologies; the U.S. has launched no other lunar probes since.

LRO will collect more data with greater precision so that scientists can find safe and resource-rich landing sites and design systems appropriate for the lunar environment, says Vondrak.

LRO will orbit the Moon for one year at an altitude of 50 kilometers. Previous U.S. satellites maintained an altitude of approximately 100 to 200 kilometers, as have those sent by other countries, like China's Chang'e 1 and Japan's Kaguya, both launched in 2007. Orbiting at a lower altitude allows the spacecraft to get a closer view of the Moon, enabling the craft to obtain higher-resolution images, very detailed maps, and more-accurate temperature measurements, says Vondrak.

The lunar orbiter is equipped with six novel instruments, two of which will be making their space debuts: a cosmic-ray telescope, which will measure the effects that lunar radiation would have on humans, and a laser altimeter, which will make maps of the surface of the Moon.

The cosmic-ray telescope, called Crater, is a new kind of sensor developed by MIT, Boston University, the University of Tennessee at Knoxville, and the Aerospace Corporation. It can measure the radiation environment, not just in space, but also as it would be experienced by astronauts on the surface on a day-to-day basis. "By characterizing the radiation, we can build better shielding on spacecraft so that astronauts can survive long trips to the Moon and Mars," says Justin Kasper, a staff astrophysicist at the Harvard-Smithsonian Center for Astrophysics and the project scientist for Crater.