NASA is developing technologies that will allow lunar landers to automatically identify and navigate to the location of a safe landing site while detecting landing hazards during the final descent to the surface. This is important because future lunar missions will need this capability to be able to land safely near specific resources that are located in potentially hazardous terrain.
Two critical sensor technologies being developed by NASA Langley Research Center will enable this capability. One is a three-dimensional active imaging device for measuring the topography of a landing area. The second is a device for measuring speed to help land precisely at the chosen site.
To help meet this dual challenge, Langley has designed two special-purpose light detection and ranging (lidar) sensors. In conjunction with this, NASA's Jet Propulsion Laboratory is developing algorithms, or mathematical procedures, for analyzing the terrain based upon these lidar measurements.
These technologies have been integrated as part of NASA's Autonomous Landing and Hazard Avoidance Technology (ALHAT) project and are in the process of being demonstrated in a series of flight tests.
Bob Reisse is leading a Langley team designing the lidar sensors and supporting the demonstration flight tests.
"We were pleased that the two flight tests we've conducted so far have resulted in better than expected performance of these sensors. The main objective of the first test, carried out in May, was to demonstrate the application of 3-D imaging technology or 'flash' lidar, for topography mapping and precision navigation.
"The second round of flight tests, completed in August, was to evaluate the capabilities of an emerging lidar technology developed at Langley, called the Doppler lidar velocimeter, also needed to meet ALHAT's stringent need for precision navigation. This lidar provides vehicle velocity vector, altitude and attitude with a very high degree of precision," Reisse said.
During this most recent test, the velocimeter was carried aloft at NASA's Dryden Flight Research Center via helicopter which flew a total of six flights at various altitudes between targeted reference points.
During the tests, the helicopter flew over two target areas three miles (5 km) apart on the surface of Rogers Dry Lake. Repeated back-and-forth tracks were flown at altitudes incrementally increasing from about 300 feet to 6,200 feet (91m to 1,890m) above the lake bed while the lidar measured the relative speed, altitude, and attitude of the helicopter. Plywood circles placed on the lakebed served as reference targets for determining the ground "truth" measurements. The data was recorded on board and tagged with time and altitude information to allow post-flight processing.
Lidar technology promises great improvements over current state-of-the-art systems for planetary navigating tasks. Preliminary results with the ALHAT Doppler lidar indicate that its "accuracy of velocity" readings and "rate of updates" are more than 10 times higher than conventional Doppler radar-based sensors like those used in Phoenix Mars Lander and Mars Science Lab.
Precision range and directional velocity data are critical to navigating lunar landing vehicles to the pre-selected site and achieving autonomous, safe soft-landing.
Data provided by ALHAT's lidar can significantly impact the design of future lunar and other planetary landing missions. The technology also has potential for aiding crew exploration vehicle rendezvous and docking, and Earth reentry landing systems.
NASA's Johnson Space Center leads the nine-year ALHAT task, begun in early 2006, for NASA's Exploration Technology Development Program. Support is also provided by Charles Stark Draper Labs and the Johns Hopkins Applied Physics Laboratory, Baltimore.
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