How to Land Safely Back on the Moon

A hazard-detection system promises safe landings for next-generation lunar explorers.

Engineers at the Charles Stark Draper Laboratory in Cambridge, MA, are developing a guidance, navigation, and control system for lunar landings that includes an onboard hazard-detection system able to spot craters, slopes, and rocks that could be dangerous to landing craft. In the Apollo missions of 40 years ago, astronauts steered the lander to a safe spot by looking out the window; the lander itself "had no eyes," says Eldon Hall, a retired Draper engineer and one of the original electronics designers for Apollo's navigation computer.

Back to the moon: Altair is NASA’s next-generation lunar lander, larger than the Apollo lander but with similar design features. It will carry four astronauts. Credit: NASA

Multimedia   Watch a test flight of the lunar landing technology.

That meant there were some close calls with Apollo, says Tye Brady, the technical director for lunar landing at Draper, who demonstrated his team's automated-landing and hazard-avoidance technology at last week's celebration of the 40th anniversary of Apollo 11. "They were really close," Brady says, "and one- to two-meter craters are deadly. You don't see them till the last minute." Apollo 11 astronaut Neil Armstrong had to steer past a field of rocks that didn't show up on any recon photos beforehand, and Apollo 14 landed at a precarious tilt with one footpad resting about a meter away from a crater.

The new navigation and guidance system is being developed for NASA's Altair lunar lander, which is scheduled to land on the moon by 2020 as part of the Constellation program. The project is headed by NASA's Johnson Space Center, with support from other NASA research facilities in addition to Draper Laboratory. The Jet Propulsion Laboratory recently completed a field test of the sensors and mapping algorithms, and it plans to begin full systems tests in May 2010.

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Brady says that the best image resolution today, such as the cameras on the orbiter now circling and photographing the moon, cannot resolve smaller holes or boulders at projected landing sites, even in smooth, well-lit areas--which aren't the targets for NASA's future landings. Altair aims to land capably at any site on the moon's surface, and the lunar terrain will vary. For that, Brady says, "you need real-time hazard detection" to adjust as you go.

Draper's system will use LIDAR laser technology to scan an area for hazards like craters or rocks before the lander touches down on the moon's surface. Raw data from LIDAR is processed and assembled into a 3-D map of the moon's surface, using algorithms developed by the Jet Propulsion Laboratory. One advantage of using LIDAR is that "it's the only type of sensor that measures the 3-D shape of what's on the ground at high resolution and from high altitude," says Andrew Johnson, the JPL lead for the hazard-detection system. That allows the system to build a terrain and elevation map of potential landing sites onboard the spacecraft, but from high enough up that there is time to respond to obstacles or craters at the landing site.