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NASA NTRS2011

Constraining the Drag Coefficients of Meteors in Dark Flight

Based on data in the aeronautics literature, we have derived functions for the drag coefficients of spheres and cubes as a function of Mach number. Experiments have shown that spheres and cubes exhibit an abrupt factor-of-two decrease in the drag coefficient as the object slows through the transonic regime. Irregularly shaped objects such as meteorites likely exhibit a similar trend. These functions are implemented in an otherwise simple projectile motion model, which is applicable to the non-ablative dark flight of meteors (speeds less than .+3 km/s). We demonstrate how these functions may be used as upper and lower limits on the drag coefficient of meteors whose shape is unknown. A Mach-dependent drag coefficient is potentially important in other planetary and astrophysical situations, for instance, in the core accretion scenario for giant planet formation.

Carter, R. T.↗

NASA NTRS2003

Compliant Gripper for a Robotic Manipulator

A figure depicts a prototype of a robotic-manipulator gripping device that includes two passive compliant fingers, suitable for picking up and manipulating objects that have irregular shapes and/or that are, themselves, compliant. The main advantage offered by this device over other robotic-manipulator gripping devices is simplicity: Because of the compliance of the fingers, force-feedback control of the fingers is not necessary for gripping objects of a variety of sizes, shapes, textures, and degrees of compliance. Examples of objects that can be manipulated include small stones, articles of clothing, and parts of plants.

Cipra, Raymond↗

NASA NTRS2012

Models Support Energy-Saving Microwave Technologies

During the Apollo Program, astronauts on the Moon encountered a small menace that created big problems: lunar dust. Similar to how tiny bits of Styrofoam behave on Earth adhering to anything they touch lunar dust sticks to spacesuits, spacecraft, tools, and equipment, and is extremely difficult to remove. The clingy nature of the substance is partly due to its electrostatic charge but is also due to its physical characteristics: The sharp, irregularly shaped grains have edges like burrs and feel like abrasive talcum powder to the touch. Not only a nuisance, Moon dust is also a potential health and safety risk. Because it is often laden with ultraviolet radiation and high iron content, it can be detrimental if it gets into the eyes or lungs. In fact, some of the particles are so small that the human body does not even detect them in order to expel them. On the Apollo missions, equipment covered with the dark-colored Moon dust suffered from the absorption of sunlight and tended to overheat. NASA has investigated tools and techniques to manage the sticky stuff, including magnets, vacuums, and shields. In 2009, Kennedy Space Center collaborated with a small business to investigate a method to harden the Moon's surface in a sense, to pave the surface so astronauts and robots could land, drive, and work without disrupting and scattering the material.

Source record↗

NASA NTRS2011

Small-Scale Features in Pulsating Aurora

A field study was conducted from March 12-16, 2002 using a narrow-field intensified CCD camera installed at Churchill, Manitoba. The camera was oriented along the local magnetic zenith where small-scale black auroral forms are often visible. This analysis focuses on such forms occurring within a region of pulsating aurora. The observations show black forms with irregular shape and nonuniform drift with respect to the relatively stationary pulsating patches. The pulsating patches occur within a diffuse auroral background as a modulation of the auroral brightness in a localized region. The images analyzed show a decrease in the brightness of the diffuse background in the region of the pulsating patch at the beginning of the offphase of the modulation. Throughout the off phase the brightness of the diffuse aurora gradually increases back to the average intensity. The time constant for this increase is measured as the first step toward determining the physical process.

Jones, Sarah↗

NASA NTRS2011

Simultaneous Multi-Filter Optical Photometry of GEO Debris

Information on the physical characteristics of unresolved pieces of debris comes from an object's brightness, and how it changes with time and wavelength. True colors of tumbling, irregularly shaped objects can be accurately determined only if the intensity at all wavelengths is measured at the same time. In this paper we report on simultaneous photometric observations of objects at geosynchronous orbit (GEO) using two telescopes at Cerro Tololo Inter-American Observatory (CTIO). The CTIO/SMARTS 0.9-m observes in a Johnson B filter, while the 0.6-m MODEST (Michigan Orbital DEbris Survey Telescope) observes in a Cousins R filter. The two CCD cameras are electronically synchronized so that the exposure start time and duration are the same for both telescopes. Thus we obtain the brightness as a function of time in two passbands simultaneously, and can determine the true color of the object at any time. We will report here on such calibrated measurements made on a sample of GEO objects and what is the distribution of the observed B-R colors. In addition, using this data set, we will show what colors would be observed if the observations in different filters were obtained sequentially, as would be the case for conventional imaging observations with a single detector on a single telescope. Finally, we will compare our calibrated colors of GEO debris with colors determined in the laboratory of selected materials actually used in spacecraft construction.

Seitzer, Patrick↗

NASA NTRS2012

Ground-Based Observations of Recovery Phase Aurora

This analysis focuses on spatial and temporal forms occurring after substorm breakup. The observations show irregular shapes and nonuniform drifts with respect to relatively stationary pulsating patches. The pulsating patches occur within a diffuse auroral background as a modulation of the auroral brightness in a localized region. The images analyzed show a decrease in the brightness of the diffuse background in the region of the pulsating patch at the beginning of the 'off' phase of the modulation. Throughout the off phase the brightness of the diffuse aurora gradually increases back to the average intensity. The time constant for this increase is measured as the first step toward determining the physical process.

Jones, Sarah L.↗

NASA NTRS2012

Surface Textures and Features Indicative of Endogenous Growth at the McCartys Flow Field, NM, as an Analog to Martian Volcanic Plains

Basaltic lavas typically form channels or tubes, which are recognized on the Earth and Mars. Although largely unrecognized in the planetary community, terrestrial inflated sheet flows also display morphologies that share many commonalities with lava plains on Mars. The McCartys lava flow field is among the youngest (approx.3000 yrs) basaltic flows in the continental United States. The southwest sections of the flow displays smooth, flat-topped plateaus with irregularly shaped pits and hummocky inter-plateau units that form a polygonal surface. Plateaus are typically elongate in map view, up to 20 m high and display lineations within the glassy crust. Lineated surfaces occasionally display small < 1m diameter lava coils. Lineations are generally straight and parallel each other, sometimes for over 100 meters. The boundaries between plateaus and depressions are also lineated and tilted to angles sometimes approaching vertical. Plateau-parallel cracks, sometimes containing squeeze-ups, mark the boundary between tilted crust and plateau. Some plateau depressions display level floors with hummocky surfaces, while some are bowl shaped with floors covered in broken lava slabs. The lower walls of pits sometimes display lateral, sagged lava wedges. Infrequently, pit floors display the upper portion of a tumulus from an older flow. In some places the surface crust has been disrupted forming a slabby texture. Slabs are typically on the scale of a meter or less across and no less than 7-10 cm thick. The slabs preserve the lineated textures of the undisturbed plateau crust. It appears that this style of terrain represents the emplacement of an extensive sheet that experiences inflation episodes within preferred regions where lateral spreading of the sheet is inhibited, thereby forming plateaus. Rough surfaces represent inflation-related disruption of pahoehoe lava and not a a lava. Depressions are often the result of non-inflation and can be clearly identified by lateral squeeze-outs along the pit walls that form when the rising crust exposes the still liquid core of the sheet. The plains of Tharsis and Elysium, Mars, display many analogous features

Bleacher, Jacob E.↗

NASA NTRS2012

Observations of GEO Debris with the Magellan 6.5-m Telescopes

Optical observations of geosynchronous orbit (GEO) debris are important to address two questions: 1. What is the distribution function of objects at GEO as a function of brightness? With some assumptions, this can be used to infer a size distribution. 2. Can we determine what the likely composition of individual GEO debris pieces is from studies of the spectral reflectance of these objects? In this paper we report on optical observations with the 6.5-m Magellan telescopes at Las Campanas Observatory in Chile that attempt to answer both questions. Imaging observations over a 0.5 degree diameter field-of-view have detected a significant population of optically faint debris candidates with R > 19th magnitude, corresponding to a size smaller than 20 cm assuming an albedo of 0.175. Many of these objects show brightness variations larger than a factor of 2, suggesting either irregular shapes or albedo variations or both. The object detection rate (per square degree per hour) shows an increase over the rate measured in the 0.6-m MODEST observations, implying an increase in the population at optically fainter levels. Assuming that the albedo distribution is the same for both samples, this corresponds to an increase in the population of smaller size debris. To study the second issue, calibrated reflectance spectroscopy has been obtained of a sample of GEO and near GEO objects with orbits in the public U.S. Space Surveillance Network catalog. With a 6.5-m telescope, the exposures times are short (30 seconds or less), and provide simultaneous wavelength coverage from 4500 to 8000 Angstroms. If the observed objects are tumbling, then simultaneous coverage and short exposure times are essential for a realistic assessment of the object fs spectral signature. We will compare the calibrated spectra with lab-based measurements of simple spacecraft surfaces composed of a single material.

Seitzer, Patrick↗

NASA NTRS2013

A Periglacial Analog for Landforms in Gale Crater, Mars

Several features in a high thermal inertia (TI) unit at Gale crater can be interpreted within a periglacial framework. These features include polygonally fractured terrain (cf. ice-wedge polygons), circumferential patterns of polygonal fractures (cf. relict pingos with ice-wedge polygons on their surfaces), irregularly-shaped and clustered depressions (cf. remnants of collapsed pingos and ephemeral lakes), and a general hummocky topography (cf. thermokarst). This interpretation would imply a major history of water and ice in Gale crater, involving permafrost, freeze-thaw cycles, and perhaps ponded surface water.

Oehler, Dorothy Z.↗

NASA NTRS2012

Numerical Simulation of Rocket Exhaust Interaction with Lunar Soil

This technology development originated from the need to assess the debris threat resulting from soil material erosion induced by landing spacecraft rocket plume impingement on extraterrestrial planetary surfaces. The impact of soil debris was observed to be highly detrimental during NASA s Apollo lunar missions and will pose a threat for any future landings on the Moon, Mars, and other exploration targets. The innovation developed under this program provides a simulation tool that combines modeling of the diverse disciplines of rocket plume impingement gas dynamics, granular soil material liberation, and soil debris particle kinetics into one unified simulation system. The Unified Flow Solver (UFS) developed by CFDRC enabled the efficient, seamless simulation of mixed continuum and rarefied rocket plume flow utilizing a novel direct numerical simulation technique of the Boltzmann gas dynamics equation. The characteristics of the soil granular material response and modeling of the erosion and liberation processes were enabled through novel first principle-based granular mechanics models developed by the University of Florida specifically for the highly irregularly shaped and cohesive lunar regolith material. These tools were integrated into a unique simulation system that accounts for all relevant physics aspects: (1) Modeling of spacecraft rocket plume impingement flow under lunar vacuum environment resulting in a mixed continuum and rarefied flow; (2) Modeling of lunar soil characteristics to capture soil-specific effects of particle size and shape composition, soil layer cohesion and granular flow physics; and (3) Accurate tracking of soil-borne debris particles beginning with aerodynamically driven motion inside the plume to purely ballistic motion in lunar far field conditions. In the earlier project phase of this innovation, the capabilities of the UFS for mixed continuum and rarefied flow situations were validated and demonstrated for lunar lander rocket plume flow impingement under lunar vacuum conditions. Applications and improvements to the granular flow simulation tools contributed by the University of Florida were tested against Earth environment experimental results. Requirements for developing, validating, and demonstrating this solution environment were clearly identified, and an effective second phase execution plan was devised. In this phase, the physics models were refined and fully integrated into a production-oriented simulation tool set. Three-dimensional simulations of Apollo Lunar Excursion Module (LEM) and Altair landers (including full-scale lander geometry) established the practical applicability of the UFS simulation approach and its advanced performance level for large-scale realistic problems.

Liever, Peter↗

NASA NTRS2012

Motion Imagery and Robotics Application (MIRA): Standards-Based Robotics

Martinez, Lindolfo↗

NASA NTRS2013

Issues and Strategies in Solving Multidisciplinary Optimization Problems

Optimization research at NASA Glenn Research Center has addressed the design of structures, aircraft and airbreathing propulsion engines. The accumulated multidisciplinary design activity is collected under a testbed entitled COMETBOARDS. Several issues were encountered during the solution of the problems. Four issues and the strategies adapted for their resolution are discussed. This is followed by a discussion on analytical methods that is limited to structural design application. An optimization process can lead to an inefficient local solution. This deficiency was encountered during design of an engine component. The limitation was overcome through an augmentation of animation into optimization. Optimum solutions obtained were infeasible for aircraft and airbreathing propulsion engine problems. Alleviation of this deficiency required a cascading of multiple algorithms. Profile optimization of a beam produced an irregular shape. Engineering intuition restored the regular shape for the beam. The solution obtained for a cylindrical shell by a subproblem strategy converged to a design that can be difficult to manufacture. Resolution of this issue remains a challenge. The issues and resolutions are illustrated through a set of problems: Design of an engine component, Synthesis of a subsonic aircraft, Operation optimization of a supersonic engine, Design of a wave-rotor-topping device, Profile optimization of a cantilever beam, and Design of a cylindrical shell. This chapter provides a cursory account of the issues. Cited references provide detailed discussion on the topics. Design of a structure can also be generated by traditional method and the stochastic design concept. Merits and limitations of the three methods (traditional method, optimization method and stochastic concept) are illustrated. In the traditional method, the constraints are manipulated to obtain the design and weight is back calculated. In design optimization, the weight of a structure becomes the merit function with constraints imposed on failure modes and an optimization algorithm is used to generate the solution. Stochastic design concept accounts for uncertainties in loads, material properties, and other parameters and solution is obtained by solving a design optimization problem for a specified reliability. Acceptable solutions can be produced by all the three methods. The variation in the weight calculated by the methods was found to be modest. Some variation was noticed in designs calculated by the methods. The variation may be attributed to structural indeterminacy. It is prudent to develop design by all three methods prior to its fabrication. The traditional design method can be improved when the simplified sensitivities of the behavior constraint is used. Such sensitivity can reduce design calculations and may have a potential to unify the traditional and optimization methods. Weight versus reliability traced out an inverted-S-shaped graph. The center of the graph corresponded to mean valued design. A heavy design with weight approaching infinity could be produced for a near-zero rate of failure. Weight can be reduced to a small value for a most failure-prone design. Probabilistic modeling of load and material properties remained a challenge.

Patnaik, Surya↗

NASA NTRS2013

Polarimetric and Multi-Doppler Radar Observations of Electrified and Unelectrified Wildfire Smoke Plumes

Pyrocumulus clouds above three Colorado wildfires (Hewlett Gulch, High Park, and Waldo Canyon; all occurred during summer 2012) electrified and produced small intracloud discharges whenever the smoke plumes grew to high altitudes (over 10 km above mean sea level, or MSL). This occurred during periods of rapid wildfire growth, as indicated by the shortwave infrared channel on a geostationary satellite, as well as by incident reports. In the Hewlett Gulch case, the fire growth led to increased updrafts within the plume, as inferred by multiple‐ Doppler radar syntheses, which led to the vertical development and subsequent electrification ‐ a life cycle as short as 30 minutes. The lightning, detected by a threedimensional lightning mapping network, was favored in high‐altitude regions (~10 km MSL) containing modest reflectivities (25 dBZ and lower), ~0 dB differential reflectivity, and reduced correlation coefficient (~0.6‐0.7). This indicated the likely presence of ice particles (crystals and aggregates, possibly rimed) mixed with ash. Though neither multiple‐Doppler nor polarimetric observations were available during the electrification of the High Park and Waldo Canyon plumes, their NEXRAD observations showed reflectivity structures consistent with Hewlett Gulch. In addition, polarimetric and multiple‐Doppler scanning of unelectrified High Park plumes indicated only irregularly shaped ash, and not ice, was present (i.e., reflectivities < 25 dBZ, differential reflectivity > 5 dB, correlation < 0.4), and there was no broaching of the 10 km altitude. Based on these results, the electrification likely was caused by ice‐based processes that did not involve significant amounts of graupel. The results demonstrate the scientific value of multiple‐Doppler and polarimetric radar observations of wildfire smoke plumes ‐ including the ability to distinguish between regions of pure hydrometeors, regions of pure ash, and mixtures of both ‐ and also suggest a possible new application for lightning data in monitoring wildfires.

Lang, Timothy J.↗

NASA NTRS2013

On the Electrification of Pyrocumulus Clouds

The electrification (or lack thereof) of pyrocumulus clouds is examined for several different wildfires that occurred during 2012‐2013. For example, pyrocumulus clouds above three Colorado wildfires (Hewlett Gulch, High Park, and Waldo Canyon; all occurred during summer 2012) electrified and produced small intracloud discharges whenever the smoke plumes grew to high altitudes (over 10 km above mean sea level, or MSL). This occurred during periods of rapid wildfire growth, as indicated by the shortwave infrared channel on a geostationary satellite, as well as by incident reports. In the Hewlett Gulch case, the fire growth led to increased updrafts within the plume, as inferred by multiple‐Doppler radar syntheses, which led to the vertical development and subsequent electrification ‐ a life cycle as short as 30 minutes. The lightning, detected by a three‐dimensional lightning mapping network, was favored in high‐altitude regions (~10 km MSL) containing modest reflectivities (25 dBZ and lower), ~0 dB differential reflectivity, and reduced correlation coefficient (~0.6‐0.7). This indicated the likely presence of ice particles (crystals and aggregates, possibly rimed) mixed with ash. Though neither multiple‐Doppler nor polarimetric observations were available during the electrification of the High Park and Waldo Canyon plumes, their NEXRAD observations showed reflectivity structures consistent with Hewlett Gulch. In addition, polarimetric and multiple‐Doppler scanning of unelectrified High Park plumes indicated only irregularly shaped ash, and not ice, was present (i.e., reflectivities < 25 dBZ, differential reflectivity > 5 dB, correlation < 0.4), and there was no broaching of the 10 km altitude. Based on these results, the electrification likely was caused by ice‐based processes that did not involve significant amounts of graupel. Results for pyrocumulus clouds above notable 2013 wildfires that also experienced rapid growth (e.g., Black Forest, Yarnell Hill, West Fork, Tres Lagunas, etc.) will be compared against the 2012 cases, with special emphasis on polarimetric NEXRAD and available lightning measurements, in order to better understand the physical processes responsible for pyrocumulus electrification.

Lang, Timothy J.↗

NASA NTRS2014

Supervolcanoes Within an Ancient Volcanic Province in Arabia Terra, Mars

Several irregularly shaped craters located within Arabia Terra, Mars represent a new type of highland volcanic construct and together constitute a previously unrecognized martian igneous province. Similar to terrestrial supervolcanoes, these low-relief paterae display a range of geomorphic features related to structural collapse, effusive volcanism, and explosive eruptions. Extruded lavas contributed to the formation of enigmatic highland ridged plains in Arabia Terra. Outgassed sulfur and erupted fine-grained pyroclastics from these calderas likely fed the formation of altered, layered sedimentary rocks and fretted terrain found throughout the equatorial region. Discovery of a new type of volcanic construct in the Arabia volcanic province fundamentally changes the picture of ancient volcanism and climate evolution on Mars. Other eroded topographic basins in the ancient Martian highlands that have been dismissed as degraded impact craters should be reconsidered as possible volcanic constructs formed in an early phase of widespread, disseminated magmatism on Mars.

Mars↗

NASA NTRS2014

Spacecraft Stabilization and Control for Capture of Non-Cooperative Space Objects

This paper addresses stabilization and control issues in autonomous capture and manipulation of non-cooperative space objects such as asteroids, space debris, and orbital spacecraft in need of servicing. Such objects are characterized by unknown mass-inertia properties, unknown rotational motion, and irregular shapes, which makes it a challenging control problem. The problem is further compounded by the presence of inherent nonlinearities, signi cant elastic modes with low damping, and parameter uncertainties in the spacecraft. Robust dissipativity-based control laws are presented and are shown to provide global asymptotic stability in spite of model uncertainties and nonlinearities. It is shown that robust stabilization can be accomplished via model-independent dissipativity-based controllers using thrusters alone, while stabilization with attitude and position control can be accomplished using thrusters and torque actuators.

Joshi, Suresh↗

NASA NTRS2014

Topical Issue on Optical Particle Characterization and Remote Sensing of the Atmosphere: Part I

Increasing our understanding of the Earth-atmosphere system has been a scientific and political priority for the last few decades. This system not only touches on environmental science, but it has applicability to our broader understanding of planetary atmospheres in general. While this issue focuses primarily on electromagnetics, other fundamental fields of science, including fluid and thermodynamics play major roles. In recent years, significant research efforts have led to advances in the fields of radiative transfer and electromagnetic scattering from irregularly shaped particles. Recently, several workshops and small conferences have taken place to promote the fusion of these efforts. Late in 2013, for instance, two such meetings took place. The Optical Characterization of Atmospheric Aerosols (OCAA) meeting took place in Smolenice, Slovakia to promote a better understanding of microphysical properties of aerosol particles, and the characterization of such atmospheric particles using optical techniques. A complementary conference was organized in Nagoya, Japan, the 3rd International Symposium on Atmospheric Light Scattering and Remote Sensing (ISALSaRS), whose goal is to fuse the advances achieved in particle characterization with remote-sensing techniques. While the focus of these meetings is slightly different, they represent the same aspects of this rapidly growing field. This Topical Issue is the first of two parts. Within this issue we analyze different aspects of the problem of atmospheric characterization and present a broad overview of the topical area. Research includes theory and experiment, ranging from fundamental microphysical properties of individual aerosol particles to broad characterizations of atmospheric properties. Since this is an active field, we also have encouraged the submission of ideas for new methodologies that may represent the future of the field.

aerosols↗

NASA NTRS2014

Grid-Free 2D Plasma Simulations of the Complex Interaction Between the Solar Wind and Small, Near-Earth Asteroids

We present results from a new grid-free 2D plasma simulation code applied to a small, unmagnetized body immersed in the streaming solar wind plasma. The body was purposely modeled as an irregular shape in order to examine photoemission and solar wind plasma flow in high detail on the dayside, night-side, terminator and surface-depressed 'pocket' regions. Our objective is to examine the overall morphology of the various plasma interaction regions that form around a small body like a small near-Earth asteroid (NEA). We find that the object obstructs the solar wind flow and creates a trailing wake region downstream, which involves the interplay between surface charging and ambipolar plasma expansion. Photoemission is modeled as a steady outflow of electrons from illuminated portions of the surface, and under direct illumination the surface forms a non-monotonic or ''double-sheath'' electric potential upstream of the body, which is important for understanding trajectories and equilibria of lofted dust grains in the presence of a complex asteroid geometry. The largest electric fields are found at the terminators, where ambipolar plasma expansion in the body-sized night-side wake merges seamlessly with the thin photoelectric sheath on the dayside. The pocket regions are found to be especially complex, with nearby sunlit regions of positive potential electrically connected to unlit negative potentials and forming adjacent natural electric dipoles. For objects near the surface, we find electrical dissipation times (through collection of local environmental solar wind currents) that vary over at least 5 orders of magnitude: from 39 Micro(s) inside the near-surface photoelectron cloud under direct sunlight to less than 1 s inside the particle-depleted night-side wake and shadowed pocket regions

Asteroids↗