Lidar Sensors for Autonomous Landing and Hazard Avoidance

Lidar technology will play an important role in enabling highly ambitious missions being envisioned for exploration of solar system bodies. Currently, NASA is developing a set of advanced lidar sensors, under the Autonomous Landing and Hazard Avoidance (ALHAT) project, aimed at safe landing of robotic and manned vehicles at designated sites with a high degree of precision. These lidar sensors are an Imaging Flash Lidar capable of generating high resolution three-dimensional elevation maps of the terrain, a Doppler Lidar for providing precision vehicle velocity and altitude, and a Laser Altimeter for measuring distance to the ground and ground contours from high altitudes. The capabilities of these lidar sensors have been demonstrated through four helicopter and one fixed-wing aircraft flight test campaigns conducted from 2008 through 2012 during different phases of their development. Recently, prototype versions of these landing lidars have been completed for integration into a rocket-powered terrestrial free-flyer vehicle (Morpheus) being built by NASA Johnson Space Center. Operating in closed-loop with other ALHAT avionics, the viability of the lidars for future landing missions will be demonstrated. This paper describes the ALHAT lidar sensors and assesses their capabilities and impacts on future landing missions

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

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 m 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 1deg FOV raster-scanning mode in which successive, gimbaled images of the hazard field are mosaicked together as well as in a wider, 4.85deg 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 Maps (DEM's) and identifies hazards and safe-landing sites which the ALHAT GN&C system can then use to guide the host vehicle to a safe landing on the selected site. Results indicate that, for the KSC hazard field, the lidar operational range extends from 100m to 1.35 km for a 30 degree line-of-sight angle and a range precision as low as 8 cm which permits hazards as small as 25 cm to be identified. Based on the Flash Lidar images, the HDS correctly found and reported safe sites in near-real-time during several of the flights. A follow-on field test, planned for 2013, seeks to complete the closing of the GN&C loop for fully-autonomous operations on-board the Morpheus robotic, rocket-powered, free-flyer test bed in which the ALHAT system would scan the KSC hazard field (which was vetted during the present testing) and command the vehicle to landing on one of the selected safe sites

Development and validation of a computational model of the knee joint for the evaluation of surgical treatments for osteoarthritis

A three-dimensional (3D) knee joint computational model was developed and validated to predict knee joint contact forces and pressures for different degrees of malalignment. A 3D computational knee model was created from high-resolution radiological images to emulate passive sagittal rotation (full-extension to 658-flexion) and weight acceptance. A cadaveric knee mounted on a six-degree-of-freedom robot was subjected to matching boundary and loading conditions. A ligamenttuning process minimised kinematic differences between the robotically loaded cadaver specimen and the finite element (FE) model. The model was validated by measured intra-articular force and pressure measurements. Percent full scale error between FE-predicted and in vitro-measured values in the medial and lateral compartments were 6.67% and 5.94%, respectively, for normalised peak pressure values, and 7.56% and 4.48%, respectively, for normalised force values. The knee model can accurately predict normalised intra-articular pressure and forces for different loading conditions and could be further developed for subject-specific surgical planning

GIFTS EDU Ground-based Measurement Experiment

Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) Engineering Demonstration Unit (EDU) is an imaging infrared spectrometer designed for atmospheric soundings. The EDU groundbased measurement experiment was held in Logan, Utah during September 2006 to demonstrate its extensive capabilities for geosynchronous and other applications

Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) Engineering Demonstation Unit (EDU) Overview and Performance Summary

The Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS), developed for the NASA New Millennium Program (NMP) Earth Observing-3 (EO-3) mission, has recently completed a series of uplooking atmospheric measurements. The GIFTS development demonstrates a series of new sensor and data processing technologies that can significantly expand geostationary meteorological observational capability. The resulting increase in forecasting accuracy and atmospheric model development utilizing this hyperspectral data is demonstrated by the uplooking data. The GIFTS sensor is an imaging FTS with programmable spectral resolution and spatial scene selection, allowing spectral resolution and area coverage to be traded in near-real time. Due to funding limitations, the GIFTS sensor module was completed as an engineering demonstration unit that can be upgraded to flight quality. This paper reviews the GIFTS system design considerations and the technology utilized to enable a nearly two order performance increase over the existing GOES sounder and shows its capability. While not designed as an operational sensor, GIFTS EDU provides a flexible and accurate testbed for the new products the hyperspectral era will bring. Efforts to find funding to upgrade and demonstrate this amazing sensor in space are continuing

TRAVAUX LASER-MATIÈRE AU CENTRE D'ÉTUDES DE LIMEIL

Les résultats d'interaction rayonnement-matière sont présentés. A 1,06 µm, l'interaction est étudiée jusqu'à des flux de 5 x 1015 W.cm-2 en focalisant le faisceau laser sur un bâtonnet de deutérium solide. A 10,6 µm les flux sont de quelques 1013 W.cm-2 sur cible d'aluminium. On observe des émissions d'ions rapides et d'électrons suprathermiques. Les quatre faisceaux du laser C6 : 600 J - 1,4 ns ont été utilisés pour imploser des microballons en verre. Les résultats expérimentaux d'implosion sont en bonne concordance avec ceux donnés par une simulation numérique monodimensionnelle. Ces expériences sont poursuivies avec le laser P102 : 80 J - 100 ps, à des puissances laser plus élevées. On décrit les lasers de puissance du laboratoire, notamment le laser OCTAL 500 J - 1,6 TW - 500 ps en cours de construction, et on en donne les caractéristiques principales.Laser-matter interaction results are presented. At 1.06 µm solid deuterium stick is irradiated till 5 x 1015 W.cm-2. At 10.6 µm, fluxes are of a few 1013 W.cm-2 on aluminium target. High energy ions and suprathermal electrons are produced. Implosions of glass shells by the four beams of the laser C6 : 600 J - 1.4 ns have been observed ; experimental and numerical results are in good agreement. Such experiments are continued with the laser Pl02 : 80 J - 100 ps at higher laser powers. Lasers used in the laboratory are described, in particular the laser OCTAL 500 J - 1.6 TW - 500 ps in process of construction, and their main features are given

Estimation of Ultrasound Induced Cavitation Bubble Temperatures in Aqueous Solutions

Mean acoustic cavitation bubble temperatures have been measured in a series of aqueous solutions containing C 1-C 5 aliphatic alcohols, at 355 kHz. The method relies on the distribution of hydrocarbon product yields produced from the recombination of methyl radicals generated on the thermal decomposition of the alcohols. The mean bubble temperature was found to decrease with increasing concentration of alcohol with the effect being more pronounced the higher the molecular weight (the lower the vapour pressure) of the alcohol. It is shown that the decrease in the temperatures measured correlates very well with an increase in the surface excess of the alcohol, similar to that previously reported for the quenching of sonoluminescence in aqueous solutions containing alcohols [J. Phys. Chem. B 101 (1997) 10845; J. Phys. Chem. B 103 (1999) 9231]. The measured temperatures ranged from 4600 ± 200 K at zero alcohol concentration to 2300 ± 200 K at 0.5 M t-butanol. The validity of the method is discussed and it is concluded that even though a number of assumptions need to be applied the results appear to indicate that the method gives an accurate measure of the mean bubble temperature. © 2004 Elsevier B.V. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Perfluorocarbons as Inert Gases in Homogeneous Sonochemistry

The polyatomic inert gases CF4 and C2F6 are efficient in homogeneous sonochemistry. This observation leads to the conclusion that some analogies could exist between sonochemistry and plasma chemistry. © 1992.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Verfahrensgrundlagen zur Herstellung von Oxidschichten fuer optische Anwendungen durch Laser-PVD. Teilvorhaben: Laser-PVD mit gepulsten Laserquellen verschiedener Wellenlaengen Abschlussbericht

The aim of the studies was the deposition of oxide films for use as optical coatings by means of oxygen ion assisted pulsed laser deposition and the investigation of their microstructural and optical properties in dependence of the deposition parameters. An excimer laser operating at 248 nm wavelength and a CO_2-TEA-laser operating at 10.6 #mu#m wavelength was used for the ablation and evaporation, respectively, of sintered Y_2O_3, HfO_2 and ZrO_2 targets as well as amorphous SiO_2 targets. The focused laser beams were scanned in spirals with constant vector velocity across the target surface. Oxygen ion bombardment of the growing films by means of an ion beam produced in an r.f. ion source aimed at the variation of the oxygen content as well as the modification of the structure and optical properties of the films. The structure, stoichiometry and surface morphology as well as the optical properties of the films, such as transmission, reflection, refractive index, absorption coefficient in the visible and ultraviolet wavelength range and the laterally resolved absorption and laser damage thresholds at the Nd:YAG-laser wagvelength of 1.06 #mu#m, were determined and the influence of the deposition parameters on those properties was examined. Both amorphous and polycrystalline films of the yttria, hafnia and zirconia with high packing density and high bulk-like refractive indices were prepared. Moreover, the refractive indices can be varied by the variation of the deposition parameters. The absorption and laser damage thresholds at 1.06 #mu#m wavelength of single films are only partly comparable with those of continuously evaporated films since the films still contain absorbing particulates. The relations between the deposition parameters and the number of those particulates, the absorption and the laser damage thresholds are shown and discussed. On the basis of the variation of the refractive index with only one deposition parameter over a range of 0.3, highly reflecting multilayer systems consisting of alternately high-refractive index and low-refractive index sublayers of only one material were prepared. (orig.)SIGLEAvailable from TIB Hannover: F97B1021+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman