Helicopter Flight Test of a Compact, Real-Time 3-D Flash Lidar for Imaging Hazardous Terrain during Planetary Landing

Abstract

A second generation, compact, real-time, air-cooled 3-D imaging Flash Lidar sensor system, developed from a number of cutting-edge components from industry and NASA, is lab characterized and helicopter flight tested under the Autonomous Precision Landing and Hazard Detection and Avoidance Technology (ALHAT) project. The ALHAT project is seeking to develop a guidance, navigation, and control (GN&C) 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 Lidar incorporates a 3-D imaging video camera based on Indium-Gallium-Arsenide Avalanche Photo Diode and novel micro-electronic technology for a 128 x 128 pixel array operating at a video rate of 20 Hz, a high pulse-energy 1.06 µm Neodymium-doped: Yttrium Aluminum Garnet (Nd:YAG) laser, a remote laser safety termination system, high performance transmitter and receiver optics with one and five degrees field-of-view (FOV), enhanced onboard thermal control, as well as a compact and self-contained suite of support electronics housed in a single box and built around a PC-104 architecture to enable autonomous operations. The Flash Lidar was developed and then characterized at two NASA-Langley Research Center (LaRC) outdoor laser test range facilities both statically and dynamically, integrated with other ALHAT GN&C subsystems from partner organizations, and installed onto a Bell UH-1H Iroquois "Huey" helicopter at LaRC. The integrated system was flight tested at the NASA-Kennedy Space Center (KSC) on simulated lunar approach to a custom hazard field consisting of rocks, craters, hazardous slopes, and safe-sites near the Shuttle Landing Facility runway starting at slant ranges of 750 m. In order to evaluate different methods of achieving hazard detection, the lidar, in conjunction with the ALHAT hazard detection and GN&C system, operates in both a narrow 1° FOV raster-scanning mode in which successive, gimbaled images of the hazard field are mosaicked together as well as in a wider, 4.85° FOV staring mode in which digital magnification, via a novel 3-D superresolution technique, is used to effectively achieve the same spatial precision attained with the more narrow FOV optics. The lidar generates calibrated and corrected 3-D range images of the hazard field in real-time and passes them to the ALHAT Hazard Detection System (HDS) which stitches the images together to generate on-the-fly Digital Elevation

3D flash lidar performance in flight testing on the Morpheus autonomous, rocket-propelled lander to a lunar-like hazard field

“…Data from FT5 showed that it was possible to visually identify a hazard smaller than the 40 cm requirement (25 cm hazard height in FT5) even with a GSD worse that the 10 cm requirement and a range precision worse than the current 8 cm. 11 Thus data from both FT5 and FT6 indicate that the 40cm hazard resolution requirement has been met. Figure 17 and Figure 18 are both DEM's each created from a single Flash Lidar range image.…”

“…Previous flight testing onboard a UH-1H helicopter to the same KSC hazard field validated the Flash Lidar's maximum operational slant range to be 1,350m. 11 Based upon data from early 2014, the reflectivity at 1.06µm of the hazard field at an incidence angle of zero is 70% which is a contributing factor to the Flash Lidar's ability to exceed its maximum operational range requirement of 750m for a 30% reflective surface. Figure 14 shows the median intensity and median slant range as a function of time for the latter portion of free-flight 15 (FF15).…”

“…Tiger Eye serial number 1004 with a fresh FPA of appropriate sensitivity and nearly devoid of dead pixels (< 1.1% of its total pixel count) was utilized for the Morpheus testing as opposed to the equivalent sensitivity Tiger Eye 1005 camera and FPA used in the previous UH-1H testing of 2012 (FT5) which had accumulated a dead pixel count of 7.1% due to humidity exposure to its unsealed FPA (unsealed since it was still experimental). 11 Other changes since the FT5 testing included replacement of the 1° compound receiver lens with a lens of equivalent FOV and throughput which did not require the single element corrective lens required by the existing one, slight increase to the divergence of the transmitter optics to increase the overfill factor for robustness to transmitter/receiver misalignment, and addition of dry-gas purge ports to the FLSH and LEB to preclude methane fume build-up from the Morpheus tank off-gassing and to provide protection from the Texas and Florida humidity. A new series of pointing metrology tests were conducted to map the unit vectors from the FPA pixels through the receiver optics to a set of fiducials hard-mounted to the FLSH frame which were in turn mapped to the navigation frame of the ALHAT system.…”

Flight testing a Real-Time Hazard Detection System for Safe Lunar Landing on the Rocket-Powered Morpheus Vehicle

“…The color gradient from top to bottom in the image is due to apparent slope caused by the viewing angle. Past flight testing at KSC onboard a NASA UH-1H helicopter has shown the flash LIDARs maximum operational range to be approximately 1350 m. 15 The minimum operational range of the flash LIDAR is dominated by saturation and defocus. The flash LIDAR incorporates an Automatic Gain Correction (AGC) algorithm which can hold the image intensity within the sensor's dynamic range down to ranges of 150 m. The flash LIDAR receiver lens is set for maximum depth of field in order to provide in-focus images at all ranges above 250 m. As an example of the hazard detection capability of the LIDAR, Fig.…”

Imaging Flash Lidar for Autonomous Safe Landing and Spacecraft Proximity Operation

“…The operation of the flash lidar was characterized during different stages of its development that included extensive laboratory experiments, dynamic truck tests, and three helicopter and one fixed-wing aircraft flight test campaigns. [21][22][23][24][25] These tests helped the development of the prototype unit and functional demonstration onboard the rocket-powered Morpheus vehicle (Fig. 5).…”