Once the map is built, the system designates safe sites based on factors like the tilt angle of the surface, the distance and fuel cost to get to a site, the position of the lander's footpads, and the crew's margin for safe distance from hazards. Based on that information, the navigation system presents astronauts with a prioritized list of three to four safe landing sites. The astronauts can then designate any of the sites as first choice, or if they are incapacitated, the system will navigate the lander automatically to the first site on its list.

The ability to land autonomously will enable both crewed and robotic missions to land safely, Brady says (while Apollo's lunar module had an automatic landing mode, it was never used). In addition to NASA's Altair, the system could be integrated into vehicles landing on near-Earth asteroids, Mars, and other planets, or used with other lunar vehicles built by private groups.

Another advantage of using LIDAR, Johnson says, is that it works under any lighting conditions. To deal with light at the moon's equator--where a "day" is equivalent to 14 Earth days, and a "night" lasts 14 Earth nights--Apollo missions had to be timed exactly, with just one launch opportunity per month, so NASA could control the craft's exposure to light and heat. But because lighting conditions are more varied and extreme at the moon's poles, with patches of light and dark from the shadows of mountains and deep craters, it will be difficult for astronauts to see to navigate. LIDAR allows the craft to "land at night, or in shadowed regions, because the light is provided by the LIDAR sensor, not the sun," Johnson says. With real-time hazard detection, he says, the launch and landing limitations of Apollo won't apply to future missions.

The challenge for a landing system, says Brady, is getting everything to happen in about 120 seconds, including hazard-detection scans to get the data, human interaction for site approval, and then hazard-avoidance maneuvers and touchdown. His team has developed a simulator to create realistic image maps of the moon's surface, in addition to using computer code from NASA for the guidance and navigation portion of the system. So far, about 20 astronauts have sampled the Draper simulation. "They're good at going slow and easy, and they're very patient," Brady says. "They do a good job relying on the system." That's a long way from the early days when the Apollo astronauts "wanted to fly the whole thing themselves," Hall says.

The Draper team continues to develop high-fidelity models of LIDAR and terrain maps, while coordinating with NASA's crew office to determine the best way to display information for astronauts. They aim to have the technology ready by 2012.