Engineering topics

Wilkinson, R. Allen

Publications and source records attributed to Wilkinson, R. Allen.

At least 19 records

NASA NTRS2014

Development and Testing of an ISRU Soil Mechanics Vacuum Test Facility

For extraterrestrial missions, earth based testing in relevant environments is key to successful hardware development. This is true for both early component level development and system level integration. For In-Situ Resource Utilization (ISRU) on the moon, hardware must interface with the surface material, or regolith, in a vacuum environment. A relevant test environment will therefore involve a vacuum chamber with a controlled, properly conditioned bed of lunar regolith simulant. However, in earth-based granular media, such as lunar regolith simulant, gases trapped within the material pore structures and water adsorbed to all particle surfaces will release when exposed to vacuum. Early vacuum testing has shown that this gas release can occur violently, which loosens and weakens the simulant, altering the consolidation state. A mid-size chamber (3.66 m tall, 1.5 m inner diameter) at the NASA Glenn Research Center has been modified to create a soil mechanics test facility. A 0.64 m deep by 0.914 m square metric ton bed of lunar simulant was placed under vacuum using a variety of pumping techniques. Both GRC-3 and LHT-3M simulant types were used. Data obtained from an electric cone penetrometer can be used to determine strength properties at vacuum including: cohesion, friction angle, bulk density and shear modulus. Simulant disruptions, caused by off-gassing, affected the strength properties, but could be mitigated by reducing pump rate. No disruptions were observed at pressures below 2.5 Torr, regardless of the pump rate. The slow off-gassing of the soil at low pressure lead to long test times; a full week to reach 10(exp -5) Torr. Robotic soil manipulation would enable multiple ISRU hardware test within the same vacuum cycle. The feasibility of a robotically controlled auger and tamper was explored at vacuum conditions.

lunar regolith↗

NASA NTRS2012

Lunar Excavation Experiments in Simulant Soil Test Beds-Revisiting the Surveyor Geotechnical Data

(1) Establishing ISRU technologies on planetary bodies is an important long-term goal of NASA; (2) Excavation is a key component of these ISRU processes; (3) Lack of flight data relevant to lunar excavation; (4) Existing models of the excavation-cutting phenomenon give varying results; (5) The lack of predictive models of the dynamic behavior of soils in excavation implements is a major driver for these studies; and (6) Objective: Need to develop robust models of excavation cutting phenomena that generate predictive capabilities to aid the designer and engineer.

Agui, Juan H.↗

NASA NTRS2010

A Review of Discrete Element Method (DEM) Particle Shapes and Size Distributions for Lunar Soil

As part of ongoing efforts to develop models of lunar soil mechanics, this report reviews two topics that are important to discrete element method (DEM) modeling the behavior of soils (such as lunar soils): (1) methods of modeling particle shapes and (2) analytical representations of particle size distribution. The choice of particle shape complexity is driven primarily by opposing tradeoffs with total number of particles, computer memory, and total simulation computer processing time. The choice is also dependent on available DEM software capabilities. For example, PFC2D/PFC3D and EDEM support clustering of spheres; MIMES incorporates superquadric particle shapes; and BLOKS3D provides polyhedra shapes. Most commercial and custom DEM software supports some type of complex particle shape beyond the standard sphere. Convex polyhedra, clusters of spheres and single parametric particle shapes such as the ellipsoid, polyellipsoid, and superquadric, are all motivated by the desire to introduce asymmetry into the particle shape, as well as edges and corners, in order to better simulate actual granular particle shapes and behavior. An empirical particle size distribution (PSD) formula is shown to fit desert sand data from Bagnold. Particle size data of JSC-1a obtained from a fine particle analyzer at the NASA Kennedy Space Center is also fitted to a similar empirical PSD function.

Lane, John E.↗

NASA NTRS2010

Granular Flow and Dynamics of Lunar Simulants in Excavating Implements

The exploration of the lunar surface will rely on properly designed excavation equipment for surface preparations and for collection of lunar regolith in In-Situ Resource Utilization (ISRU) processes. Performance efficiency, i.e minimizing loading forces while maximizing material collection, and mass and volume reductions are major design goals. The NASA Glenn Research Center has embarked on an experimental program to determine the flow characteristics and dynamic forces produced by excavation operations using various excavator bucket designs. A new large scale soil bin facility, 2.27 m x 5.94 m x 0.76 m (nominally 8 ft. x 20 ft. x 27 in.) in size, capable of accommodating moderately large test implements was used for the simulations of lunar operations. The soil bin is filled with GRC-3simulant (a mixture of industrial sands and silt with a particle size distribution and the bulk mechanical (shear) strength representative of an average of lunar regolith from different regions) and uses motorized horizontal rails and a vertical actuator to drive the implement through the lunar simulant soil. A six-axis load cell and encoders provide well resolved measurements of the three dimensional forces and torques and motion of the bucket. In addition, simultaneous video allows for the analysis of the flow behavior and structure formation of the regolith during excavation. The data may be useful in anchoring soil mechanic models and to provide engineering data for design consideration.

Agui, Juan H.↗

NASA NTRS2010

Comparison of ISRU Excavation System Model Blade Force Methodology and Experimental Results

An Excavation System Model has been written to simulate the collection and transportation of regolith on the Moon. The calculations in this model include an estimation of the forces on the digging tool as a result of excavation into the regolith. Verification testing has been performed and the forces recorded from this testing were compared to the calculated theoretical data. A prototype lunar vehicle built at the NASA Johnson Space Center (JSC) was tested with a bulldozer type blade developed at the NASA Kennedy Space Center (KSC) attached to the front. This is the initial correlation of actual field test data to the blade forces calculated by the Excavation System Model and the test data followed similar trends with the predicted values. This testing occurred in soils developed at the NASA Glenn Research Center (GRC) which are a mixture of different types of sands and whose soil properties have been well characterized. Three separate analytical models are compared to the test data.

Gallo, Christopher A.↗

NASA NTRS2009

Lightweight Bulldozer Attachment for Construction and Excavation on the Lunar Surface

A lightweight bulldozer blade prototype has been designed and built to be used as an excavation implement in conjunction with the NASA Chariot lunar mobility platform prototype. The combined system was then used in a variety of field tests in order to characterize structural loads, excavation performance and learn about the operational behavior of lunar excavation in geotechnical lunar simulants. The purpose of this effort was to evaluate the feasibility of lunar excavation for site preparation at a planned NASA lunar outpost. Once the feasibility has been determined then the technology will become available as a candidate element in the NASA Lunar Surface Systems Architecture. In addition to NASA experimental testing of the LANCE blade, NASA engineers completed analytical work on the expected draft forces using classical soil mechanics methods. The Colorado School of Mines (CSM) team utilized finite element analysis (FEA) to study the interaction between the cutting edge of the LANCE blade and the surface of soil. FEA was also used to examine various load cases and their effect on the lightweight structure of the LANCE blade. Overall it has been determined that a lunar bulldozer blade is a viable technology for lunar outpost site preparation, but further work is required to characterize the behavior in 1/6th G and actual lunar regolith in a vacuum lunar environment.

Mueller, Robert↗

NASA NTRS2004

Granular Materials and the Risks They Pose for Success on the Moon and Mars

Wilkinson, R. Allen↗

NASA NTRS2004

Granular Materials and Risks In ISRU

Working with soil, sand, powders, ores, cement and sintered bricks, excavating, grading construction sites, driving off-road, transporting granules in chutes and pipes, sifting gravel, separating solids from gases, and using hoppers are so routine that it seems straightforward to execute these operations on the Moon and Mars as we do on Earth. We discuss how little these processes are understood and point out the nature of trial-and-error practices that are used in today's massive over-design. Nevertheless, such designs have a high failure rate. Implementation and extensive incremental scaling up of industrial processes are routine because of the inadequate predictive tools for design. We present a number of pragmatic scenarios where granular materials play a role, the risks involved, what some of the basic issues are, and what understanding is needed to greatly reduce the risks. This talk will focus on a particular class of granular flow issues, those that pertain to dense materials, their physics, and the failure problems associated with them. In particular, key issues where basic predictability is lacking include stability of soils for the support of vehicles and facilities, ability to control the flow of dense materials (jamming and flooding/unjamming at the wrong time), the ability to predict stress profiles (hence create reliable designs) for containers such as bunkers or silos. In particular, stress fluctuations, which are not accounted for in standard granular design models, can be very large as granular materials flows, and one result is frequent catastrophic failure of granular devices.

Behringer, Robert P.↗

NASA NTRS2001

Growth and Morphology of Supercritical Fluids, a Fluid Physics Experiment Conducted on Mir, Complete

The Growth and Morphology of Supercritical Fluids (GMSF) is an international experiment facilitated by the NASA Glenn Research Center and under the guidance of U.S. principal investor Professor Hegseth of the University of New Orleans and three French coinvestigators: Daniel Beysens, Yves Garrabos, and Carole Chabot. The GMSF experiments were concluded in early 1999 on the Russian space station Mir. The experiments spanned the three science themes of near-critical phase separation rates, interface dynamics in near-critical boiling, and measurement of the spectrum of density fluctuation length scales very close to the critical point. The fluids used were pure CO2 or SF6. Three of the five thermostats used could adjust the sample volume with the scheduled crew time. Such a volume adjustment enabled variable sample densities around the critical density as well as pressure steps (as distinct from the usual temperature steps) applied to the sample. The French-built ALICE II facility was used for these experiments. It allows tightly thermostated (left photograph) samples (right photograph) to be controlled and viewed/measured. Its diagnostics include interferometry, shadowgraph, high-speed pressure measurements, and microscopy. Data were logged on DAT tapes, and PCMCIA cards and were returned to Earth only after the mission was over. The ground-breaking near critical boiling experiment has yielded the most results with a paper published in Physical Review Letters (ref. 1). The boiling work also received press in Science Magazine (ref. 2). This work showed that, in very compressible near-critical two-phase pure fluids, a vapor bubble was induced to temporarily overheat during a rapid heating of the sample wall. The temperature rise in the vapor was 23-percent higher than the rise in the driving container wall. The effect is due to adiabatic compression of the vapor bubble by the rapid expansion of fluid near the boundary during heatup. Thermal diffusivity is low near the critical point, so getting heat out of the compressed bubble is observably slow. This gives the appearance of a backward heat flow, or heat flow from a cold surface to a warm fluid.

Wilkinson, R. Allen↗

NASA NTRS2000

Growth and Morphology of Supercritical Fluids Studied in Microgravity on Mir

The Growth and Morphology of Supercritical Fluids (GMSF) is an international experiment facilitated by the NASA Glenn Research Center at Lewis Field and under the guidance of U.S. principal investigator Professor John Hegseth of the University of New Orleans and three French coinvestigators Daniel Beysens, Yves Garrabos, and Carole Chabot. In early 1999, GMSF experiments were operated for 20 days on the Russian Space Station Mir. Mir astronauts performed experiments One through Seven, which spanned the three science themes of near-critical phase separation rates, interface dynamics in near-critical boiling, and measurement of the spectrum of density fluctuation length scales very close to the critical point. The fluids used were pure CO2 or SF6. Three of the five thermostats used could adjust the sample volume with the scheduled crew time. Such a volume adjustment enabled variable sample densities around the critical density as well as pressure steps (as distinct from the usual temperature steps) to be applied to the sample.

Wilkinson, R. Allen↗

NASA NTRS2000

Density Relaxation of Liquid-Vapor Critical Fluids Examined in Earth's Gravity

This work shows quantitatively the pronounced differences between the density equilibration of very compressible dense fluids in Earth's gravity and those in microgravity. The work was performed onsite at the NASA Glenn Research Center at Lewis Field and is complete. Full details are given in references 1 and 2. Liquid-vapor critical fluids (e.g., water) at their critical temperature and pressure, are very compressible. They collapse under their own weight in Earth's gravity, allowing only a thin meniscus-like layer with the critical pressure to survive. This critical layer, however, greatly slows down the equilibration process of the entire sample. A complicating feature is the buoyancy-driven slow flows of layers of heavier and lighter fluid. This work highlights the incomplete understanding of the hydrodynamics involved in these fluids.

Wilkinson, R. Allen↗

NASA NTRS2000

Remote Control and Data Acquisition: A Case Study

This paper details software tools developed to remotely command experimental apparatus, and to acquire and visualize the associated data in soft real time. The work was undertaken because commercial products failed to meet the needs. This work has identified six key factors intrinsic to development of quality research laboratory software. Capabilities include access to all new instrument functions without any programming or dependence on others to write drivers or virtual instruments, simple full screen text-based experiment configuration and control user interface, months of continuous experiment run-times, order of 1% CPU load for condensed matter physics experiment described here, very little imposition of software tool choices on remote users, and total remote control from anywhere in the world over the Internet or from home on a 56 Kb modem as if the user is sitting in the laboratory. This work yielded a set of simple robust tools that are highly reliable, resource conserving, extensible, and versatile, with a uniform simple interface.

DeGennaro, Alfred J.↗

NASA NTRS1999

Electrostriction of a Near-Critical Fluid in Microgravity

We used interferometry to measure the electrostrictive increase of the density of sulfur hexaflouride (SF6) near its critical point. The results at three temperatures (T(sub c) + 5.0 mK, T(sub c) + 10.0 mK, T(sub c) + 30.0 mK with T(sub c) = 319 K) agree with a calculation based on the Clausius-Mossotti relation and the restricted cubic model equation of state. To measure electrostriction, an inhomogeneous electric field (less than or equal to 26 kV/cm) was applied to the SF6 sample by charging a fine wire that passed through it. These measurements were performed in microgravity so that the small electrostrictive density changes (less than or equal to 3.5 % in this work) would not be masked by the larger stratification of the fluid's density induced by the Earth's gravity. The predicted shifts of the critical temperature and density resulting from the electric field were too small to detect.

Zimmerli, Gregory A.↗

NASA NTRS1998

Second Flight of the Zeno Experiment on USMP-3

The second flight of the Zeno experiment in the USMP-3 flight has shown successful control of density perturbations near the window surfaces. These density changes were demonstrated to be arising from the rate of temperature change in the sample cell during the flight. These effects could be controlled by using decreasing ramp rates as Tc was approached. The cell window interference was carefully recorded to provide data about the phase of the interference close to the critical point and the effective window reflectivity. Correlograms were recorded from 500 mili K down to 2 mili K at 24 temperatures, 383 correlograms in all. The efforts to get closer were prevented by a long (greater than two week time constant) decay of a 1.3% density error caused by local heating from the 17 micro W laser beam. The phase boundary was located with unprecedented precision of +/- 2O micro K. The complete experiment sequence was done with ground commanding and uploaded script files, bypassing the original autonomous-mode program sequence.

Gammon, Robert W.↗

NASA NTRS1998

Data Analysis of a Space Experiment: Common Software Tackles Uncommon Task

Presented here are the software adaptations developed by laboratory scientists to process the space experiment data products from three experiments on two International Microgravity Laboratory Missions (IML-1 and IML-2). The challenge was to accommodate interacting with many types of hardware and software developed by both European Space Agency (ESA) and NASA aerospace contractors, where data formats were neither commercial nor familiar to scientists. Some of the data had been corrupted by bit shifting of byte boundaries. Least-significant/most-significant byte swapping also occurred as might be expected for the various hardware platforms involved. The data consisted of 20 GBytes per experiment of both numerical and image data. A significant percentage of the bytes were consumed in NASA formatting with extra layers of packetizing structure. It was provided in various pieces to the scientists on magnetic tapes, Syquest cartridges, DAT tapes, CD-ROMS, analog video tapes, and by network FIP. In this paper I will provide some science background and present the software processing used to make the data useful in the months after the missions.

Wilkinson, R. Allen↗

NASA NTRS1996

Zeno: Critical Fluid Light Scattering Experiment

The Zeno (Critical Fluid Light Scattering) experiment is the culmination of a long history of critical fluid light scattering in liquid-vapor systems. The major limitation to making accurate measurements closer to the critical point was the density stratification which occurs in these extremely compressible fluids. Zeno was to determine the critical density fluctuation decay rates at a pair of supplementary angles in the temperature range 100 mK to 100 (mu)K from T(sub c) in a sample of xenon accurately loaded to the critical density. This paper gives some highlights from operating the instrument on two flights March, 1994 on STS-62 and February, 1996 on STS-75. More detail of the experiment Science Requirements, the personnel, apparatus, and results are displayed on the Web homepage at http://www.zeno.umd.edu.

Gammon, Robert W.↗

NASA NTRS1995

Highlights of the Zeno Results from the USMP-2 Mission

The Zeno instrument, a High-precision, light-scattering spectrometer, was built to measure the decay rates of density fluctuations in xenon near its liquid-vapor critical point in the low-gravity environment of the U.S. Space Shuttle. Eliminating the severe density gradients created in a critical fluid by Earth's gravity, we were able to make measurements to within 100 microKelvin of the critical point. The instrument flew for fourteen days in March, 1994 on the Space Shuttle Columbia, STS-62 flight, as part of the very successful USMP-2 payload. We describe the instrument and document its performance on orbit, showing that it comfortably reached the desired 3 microKelvin temperature control of the sample. Locating the critical temperature of the sample on orbit was a scientific challenge; we discuss the advantages and short-comings of the two techniques we used. Finally we discuss problems encountered with making measurements of the turbidity of the sample, and close with the results of the measurement of the decay rates of the critical-point fluctuations.

Gammon, Robert W.↗

NASA NTRS1992

Critical fluid thermal equilibration experiment (19-IML-1)

Gravity sometimes blocks all experimental techniques of making a desired measurement. Any pure fluid possesses a liquid-vapor critical point. It is defined by a temperature, pressure, and density state in thermodynamics. The critical issue that this experiment attempts to understand is the time it takes for a sample to reach temperature and density equilibrium as the critical point is approached; is it infinity due to mass and thermal diffusion, or do pressure waves speed up energy transport while mass is still under diffusion control. The objectives are to observe: (1) large phase domain homogenization without and with stirring; (2) time evolution of heat and mass after temperature step is applied to a one phase equilibrium sample; (3) phase evolution and configuration upon going two phase from a one phase equilibrium state; (4) effects of stirring on a low g two phase configuration; (5) two phase to one phase healing dynamics starting from a two phase low g configuration; and (6) effects of shuttle acceleration events on spatially and temporally varying compressible critical fluid dynamics.

Wilkinson, R. Allen↗