For the first time, a 3-D imaging Flash Lidar instrument has been used in flight to scan a lunar-like hazard field, build a 3-D Digital Elevation Map (DEM), identify a safe landing site, and, in concert with an experimental Guidance, Navigation, and Control system, help to guide the Morpheus autonomous, rocket-propelled, free-flying lander to that safe site on the hazard field. The flight tests served as the TRL 6 demo of the Autonomous Precision Landing and Hazard Detection and Avoidance Technology (ALHAT) system and included launch from NASA-Kennedy, a lunar-like descent trajectory from an altitude of 250m, and landing on a lunar-like hazard field of rocks, craters, hazardous slopes, and safe sites 400m down-range. The ALHAT project developed a system capable of enabling safe, precise crewed or robotic landings in challenging terrain on planetary bodies under any ambient lighting conditions. The Flash Lidar is a second generation, compact, real-time, air-cooled instrument. Based upon extensive on-ground characterization at flight ranges, the Flash Lidar was shown to be capable of imaging hazards from a slant range of 1 km with an 8 cm range precision and a range accuracy better than 35 cm, both at 1-σ. The Flash Lidar identified landing hazards as small as 30 cm from the maximum slant range which Morpheus could achieve (450 m); however, under certain wind conditions it was susceptible to scintillation arising from air heated by the rocket engine and to pre-triggering on a dust cloud created during launch and transported down-range by wind.
NASA has been pursuing flash lidar technology for autonomous, safe landing on solar system bodies and for automated rendezvous and docking. During the final stages of landing, from about 1 km to 500 m above the ground, the flash lidar can generate 3-Dimensional images of the terrain to identify hazardous features such as craters, rocks, and steep slopes. The onboard flight computer can then use the 3-D map of terrain to guide the vehicle to a safe location. As an automated rendezvous and docking sensor, the flash lidar can provide relative range, velocity, and bearing from an approaching spacecraft to another spacecraft or a space station. NASA Langley Research Center has developed and demonstrated a flash lidar sensor system capable of generating 16k pixels range images with 7 cm precision, at a 20 Hz frame rate, from a maximum slant range of 1800 m from the target area. This paper describes the lidar instrument and presents the results of recent flight tests onboard a rocket-propelled free-flyer vehicle (Morpheus) built by NASA Johnson Space Center. The flights were conducted at a simulated lunar terrain site, consisting of realistic hazard features and designated landing areas, built at NASA Kennedy Space Center specifically for this demonstration test. This paper also provides an overview of the plan for continued advancement of the flash lidar technology aimed at enhancing its performance to meet both landing and automated rendezvous and docking applications.
This paper describes the results of a 3D super-resolution algorithm applied to the range data obtained from a recent Flash Lidar helicopter flight test. The flight test was conducted by the NASA’s Autonomous Landing and Hazard Avoidance Technology (ALHAT) project over a simulated lunar terrain facility at NASA Kennedy Space Center. ALHAT is developing the technology for safe autonomous landing on the surface of celestial bodies: Moon, Mars, asteroids. One of the test objectives was to verify the ability of 3D super-resolution technique to generate high resolution digital elevation models (DEMs) and to determine time resolved relative positions and orientations of the vehicle. 3D super-resolution algorithm was developed earlier and tested in computational modeling, and laboratory experiments, and in a few dynamic experiments using a moving truck. Prior to the helicopter flight test campaign, a 100mX100m hazard field was constructed having most of the relevant extraterrestrial hazard: slopes, rocks, and craters with different sizes. Data were collected during the flight and then processed by the super-resolution code. The detailed DEM of the hazard field was constructed using independent measurement to be used for comparison. ALHAT navigation system data were used to verify abilities of super-resolution method to provide accurate relative navigation information. Namely, the 6 degree of freedom state vector of the instrument as a function of time was restored from super-resolution data. The results of comparisons show that the super-resolution method can construct high quality DEMs and allows for identifying hazards like rocks and craters within the accordance of ALHAT requirements.
Two flash lidars, integrated from a number of cutting-edge components from industry and NASA, are lab characterized
and flight tested for determination of maximum operational range under the Autonomous Landing and Hazard
Avoidance Technology (ALHAT) project (in its fourth development and field test cycle) which is seeking to develop a
guidance, navigation, and control (GNC) and sensing system based on lidar technology capable of enabling safe,
precise crewed or robotic landings in challenging terrain on planetary bodies under any ambient lighting conditions. The
flash lidars incorporate pioneering 3-D imaging cameras based on Indium-Gallium-Arsenide Avalanche Photo Diode
(InGaAs APD) and novel micro-electronic technology for a 128 x 128 pixel array operating at 30 Hz, high pulse-energy
1.06 μm Nd:YAG lasers, and high performance transmitter and receiver fixed and zoom optics. The two flash lidars are
characterized on the NASA-Langley Research Center (LaRC) Sensor Test Range, integrated with other portions of the
ALHAT GNC system from partner organizations into an instrument pod at NASA-JPL, integrated onto an Erickson
Aircrane Helicopter at NASA-Dryden, and flight tested at the Edwards AFB Rogers dry lakebed over a field of humanmade
geometric hazards during the summer of 2010. Results show that the maximum operational range goal of 1 km is
met and exceeded up to a value of 1.2 km. In addition, calibrated 3-D images of several hazards are acquired in realtime
for later reconstruction into Digital Elevation Maps (DEM’s).
A novel method for enhancement of the spatial resolution of 3-diminsional Flash Lidar images is being proposed for
generation of elevation maps of terrain from a moving platform. NASA recognizes the Flash LIDAR technology as
an important tool for enabling safe and precision landing in future unmanned and crewed lunar and planetary
missions. The ability of the Flash LIDAR to generate 3-dimensional maps of the landing site area during the final
stages of the descent phase for detection of hazardous terrain features such as craters, rocks, and steep slopes is
under study in the frame of the Autonomous Landing and Hazard Avoidance (ALHAT) project. Since single frames
of existing FLASH LIDAR systems are not sufficient to build a map of entire landing site with acceptable spatial
resolution and precision, a super-resolution approach utilizing multiple frames has been developed to overcome the
instrument's limitations. Performance of the super-resolution algorithm has been analyzed through a series of
simulation runs obtained from a high fidelity Flash LIDAR model and a high resolution synthetic lunar elevation
map. For each simulation run, a sequence of FLASH LIDAR frames are recorded and processed as the spacecraft
descends toward the landing site. Simulations runs having different trajectory profiles and varying LIDAR look
angles of the terrain are also analyzed. The results show that adequate levels of accuracy and precision are achieved
for detecting hazardous terrain features and identifying safe areas of the landing site.
In this paper a new image processing technique for flash LIDAR data is presented as a potential tool to enable
safe and precise spacecraft landings in future robotic or crewed lunar and planetary missions. Flash LIDARs
can generate, in real-time, range data that can be interpreted as a 3-dimensional (3-D) image and transformed
into a corresponding digital elevation map (DEM). The NASA Autonomous Landing and Hazard Avoidance
(ALHAT) project is capitalizing on this new technology by developing, testing and analyzing flash LIDARs
to detect hazardous terrain features such as craters, rocks, and slopes during the descent phase of spacecraft
landings. Using a flash LIDAR for this application looks very promising, however through theoretical and
simulation analysis the ALHAT team has determined that a single frame, or mosaic, of flash LIDAR data may
not be sufficient to build a landing site DEM with acceptable spatial resolution, precision, size, or for a mosaic,
in time, to meet current system requirements. One way to overcome this potential limitation is by enhancing
the flash LIDAR output images. We propose a new super-resolution algorithm applicable to flash LIDAR range
data that will create a DEM with sufficient accuracy, precision and size to meet current ALHAT requirements.
The performance of our super-resolution algorithm is analyzed by processing data generated during a series of
simulation runs by a high fidelity model of a flash LIDAR imaging a high resolution synthetic lunar elevation
map. The flash LIDAR model is attached to a simulated spacecraft by a gimbal that points the LIDAR to a
target landing site. For each simulation run, a sequence of flash LIDAR frames is recorded and processed as
the spacecraft descends toward the landing site. Each run has a different trajectory profile with varying LIDAR
look angles of the terrain. We process the output LIDAR frames using our SR algorithm and the results show
that the achieved level of accuracy and precision of the SR generated landing site DEM is more than adequate
for detecting hazardous terrain features and identifying safe areas.
NASA considers Flash Lidar a critical technology for enabling autonomous safe landing of future large robotic and
crewed vehicles on the surface of the Moon and Mars. Flash Lidar can generate 3-Dimensional images of the terrain to
identify hazardous features such as craters, rocks, and steep slopes during the final stages of descent and landing. The
onboard flight comptuer can use the 3-D map of terain to guide the vehicle to a safe site.
The capabilities of Flash Lidar technology were evaluated through a series of static tests using a calibrated target and
through dynamic tests aboard a helicopter and a fixed wing airctarft. The aircraft flight tests were perfomed over Moonlike
terrain in the California and Nevada deserts. This paper briefly describes the Flash Lidar static and aircraft flight test
results. These test results are analyzed against the landing application requirements to identify the areas of technology
improvement. The ongoing technology advancement activities are then explained and their goals are described.
Data from the first Flight Test of the NASA Langley Flash Lidar system have been processed. Results of the
analyses are presented and discussed. A digital elevation map of the test site is derived from the data, and is
compared with the actual topography. The set of algorithms employed, starting from the initial data sorting, and
continuing through to the final digital map classification is described. The accuracy, precision, and the spatial and
angular resolution of the method are discussed.