THE EXPERIMENTAL PERFORMANCE OF A CROSSED-FIELD PLASMA ACCELERATOR
Results of an experimental program to develop a steady-state crossed-field plasma accelerator, with attention to the materials erosion problems
PLASMA ACCELERATOR↗
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EXPERIMENTAL PERFORMANCE OF A CROSSED-FIELD PLASMA ACCELERATOR
Results of an experimental program to develop a steady-state crossed-field plasma accelerator, with attention to the materials erosion problems
PLASMA ACCELERATOR↗
Reach performance while wearing the Space Shuttle launch and entry suit during exposure to launch accelerations
Crewmen aboard the Space Shuttle are subjected to accelerations during ascent (the powered flight phase of launch) which range up to +3 G(sub x). Despite having 33 missions and nine years experience, not to mention all the time spent in development prior to the first flight, no truly quantitative reach study wearing actual crew equipment, using actual Shuttle seats and restraints has ever been done. What little information exists on reach performance while under acceleration has been derived primarily from subjective comments gathered retrospectively from Shuttle flight crews during their post mission debrief. This lack of reach performance data has resulted in uncertainty regarding emergency procedures that can realistically be performed during and actual Shuttle ascent versus what is practiced in the ground-fixed and motion-based Shuttle Simulators. With the introduction on STS-26 of the current Shuttle escape system, the question of reach performance under launch accelerations was once again raised. The escape system's requirement that each crewman wear a Launch/Entry Suit (LES), parachute harness, and parachute were all anticipated to contribute to a further degradation of reach performance during Shuttle ascent accelerations. In order to answer the reach performance question in a quantitative way, a photogrammetric method was chosen so that the actual reach values and associated envelopes could be captured. This would allow quantitative assessment of potential task performance impact and identify areas where changes to our Shuttle ascent emergency procedures might be required. Also, such a set of reach values would be valid for any similar acceleration profile using the same crew equipment. Potential Space Station applications of this data include predicting reach performance during Assured Crew Return Vehicle (ACRV) operations.
Bagian, James P.↗
Effects of Different Lifting Cadences on Ground Reaction Forces during the Squat Exercise
The purpose of this investigation was to determine the effect of different cadences on the ground reaction force (GRF(sub R)) during the squat exercise. It is known that squats performed with greater acceleration will produce greater inertial forces; however, it is not well understood how different squat cadences affect GRF(sub R). It was hypothesized that faster squat cadences will result in greater peak GRF(sub R). METHODS: Six male subjects (30.8+/-4.4 y, 179.5+/-8.9 cm, 88.8+/-13.3 kg) with previous squat experience performed three sets of three squats using three different cadences (FC = 1 sec descent/1 sec ascent; MC = 3 sec descent/1 sec ascent; SC = 4 sec descent/2 sec ascent) with barbell mass equal to body mass. Ground reaction force was used to calculate inertial force trajectories of the body plus barbell (FI(sub system)). Forces were normalized to body mass. RESULTS: Peak GRF(sub R) and peak FI(sub system) were significantly higher in FC squats compared to MC (p=0.0002) and SC (p=0.0002). Range of GRF(sub R) and FI(sub system) were also significantly higher in FC compared to MC (p<0.05), and MC were significantly higher than SC (p<0.05). DISCUSSION: Faster squat cadences result in significantly greater peak GRF(sub R) due to the inertia of the system. GRF(sub R) was more dependent upon decent cadence than on ascent cadence. PRACTICAL APPLICATION: This study demonstrates that faster squat cadences produce greater ground reaction forces. Therefore, the use of faster squat cadences might enhance strength and power adaptations to long-term resistance exercise training. Key Words: velocity, weight training, resistive exercise
Bentley, Jason R.↗
Convergence and stability properties of minimal polynomial and reduced rank extrapolation algorithms
The minimal polynomial and reduced rank extrapolation algorithms are two acceleration of convergence methods for sequences of vectors. In a recent survey these methods were tested and compared with the scalar, vector, topological epsilon algorithms, and were observed to be more efficient than the latter. It was also observed that the two methods have similar convergence properties. The convergence and stability properties of these methods are analyzed and the performance of the acceleration methods when applied to a class of vector sequences that includes those sequences obtained from systems of linear equations by using matrix iterative methods is discussed.
Sidi, A.↗
Testing and analysis of photovoltaic modules for electrochemical corrosion
This paper describes the testing and evaluation used to characterize the mechanisms of electrochemical corrosion of photovoltaic modules - encapsulated solar cells. Accelerated exposure testing was performed on a sample matrix of cell/encapsulant combinations, and microanalytical failure analysis was performed on selected samples to confirm the correlation between the accelerated test data and the life prediction model. A quantitative correlation between field exposure time and exposure time in the accelerated multistress tests was obtained based upon the observation that equal quantities of interelectrode charge transfer resulted in equivalent degrees of electrochemical charge.
Neff, Michael↗
Wall-modeled LES of Turbulent Flow Over a Two-dimensional Gaussian Bump
We perform wall-modeled large eddy simulations (WMLES) of turbulent flow over a nominally two-dimensional Gaussian-shaped bump geometry to assess its performance in the accelerating and separation regions of the flow. The flow conditions are based on high-fidelity numerical simulation of Uzun & Malik (AIAA Journal 2022). The oncoming flow Mach number is 0.2, with the bump length-based Reynolds number (ReL) of 2 million. In our previous study, while WMLES with the constant coefficient Vreman subgrid scale model and equilibrium wall model performed satisfactorily at lower ReL = 1 million, it failed to predict flow separation at the higher Re, contrary to the experimental observations. We investigate the sensitivity of WMLES to different subgrid scale models, wall models, and grid resolution and topology on flow separation by comparing with available data.
Computational Fluid Dynamics↗
Wall-modeled LES of Flow Over a Gaussian Bump
We perform wall-modeled large eddy simulations (WMLES) of turbulent flow over a Gaussian-shaped bump geometry, to assess its performance in the accelerating and separation regions of the flow. The flow conditions are based on the ongoing CFD validation experiments of Slotnick [NATO STO-MP-AVT-307, 2019]. The oncoming flow Mach number is 0.176, and two Reynolds numbers are simulated that are about 10000 and 36000 based on boundary layer thickness upstream of the bump. Preliminary Reynolds-averaged Navier-Stokes simulations are first performed to assess the effects of Mach number, Reynolds number, tunnel top and sidewall effects. Finally, WMLES results with an equilibrium wall model will be presented at two Reynolds numbers to assess their performance for this flow by making detailed comparisons with available experimental and higher-fidelity numerical data.
turbulence, wall model, large eddy simulation↗
The new challenge of computational aeroscience
This paper discusses NASA's Computational Aerosciences (CAS) Project of the High Performance Computing and Communications Program (HPCCP). The project is aimed at developing advanced, multidisciplinary simulation capabilities for aerospace vehicle and propulsion system design. It is also aimed at overcoming computational performance barriers by accelerating the development of parallel computer technology. The goals and approach of the CAS Project are described and the challenges to its implementation are addressed. Specific vehicle class simulations to be demonstrated and the principal mutidisciplinary modeling approaches to be emphasized are described. The computational speed and memory requirements for representative multidisciplinary applications are estimated. Finally, the state of parallel computer technology including programming issues and the results of performance measurements are explored.
Bailey, F. R.↗
Preliminary tests of insulated accelerator grid for electron-bombardment thrustor
Performance tests of single ceramic protected metallic accelerator grid for direct current electron bombardment thrustor
GRID↗
Cycle-powered short radius (1.9M) centrifuge: exercise vs. passive acceleration
A human-powered short-arm centrifuge is described. This centrifuge could be used during spaceflight to provide +Gz acceleration while subjects performed exercise, thus supplying two forms of weightlessness countermeasures. Results from a study of cardiovascular responses while using the centrifuge are presented.
NASA Center ARC↗
Integration of a Fire Detector into a Spacecraft
A detector sensitive to only the ultraviolet radiation emitted by flames has been selected as the basic element of the NASA Skylab fire detection system. It is sensitive to approximately 10(exp -12)W of radiation and will detect small flames at distances in excess of 3m. The performance of the detector was verified by experiments in an aircraft flying zero-gravity parabolas to simulate the characteristics of a fire which the detector must sense. Extensive investigation and exacting design was necessary to exclude all possible sources of false alarms. Optical measurements were made on all the spacecraft windows to determine the amount of solar radiation transmitted. The lighting systems and the onboard experiments also were appraised for ultraviolet emissions. Proton-accelerator tests were performed to determine the interaction of the Earth's trapped radiation belts with the detectors and the design of the instrument was modified to negate these effects.
Linford, R. M. F.↗
Analysis of Bare-Tether Systems as a Thruster for MXER Studies
The concept of the electrodynamic propulsion has a number of attractive features and has been widely discussed for different applications. A number of system designs have been proposed and compared during the last ten years. In spite of this, the choice of the proper design, for a specific mission, is far from evident. Such characteristics of tether performance as system acceleration, efficiency, etc. should be calculated and compared. The code that calculates the current for bare and partly insulated tethers with circular (wire) and rectangle (tape) cross-sections is presented. It takes into account the corrections to the OML current due to the tether cross-section geometry and the magnetic field produced by the tether current. There are two options in this code: for current calculation with the prescribed energy supply and with the prescribed end-point potential. This permits to calculate the parameters characterizing tether performance. Results for the current calculated for tethers with different designs for the currently proposed Momentum exchange Electrodynamic Reboost (MXER) Tether System are presented.
Khazanov, G. V.↗
Analysis of Bare-Tether Systems as a Thruster for MXER Studies
The concept of the electrodynamic propulsion has a number of attractive features and has been widely discussed for different applications. A number of system designs have been proposed and compared during the last ten years. In spite of this, the choice of the proper design, for a specific mission, is far from evident. Such characteristics of tether performance as system acceleration, efficiency, etc. should be calculated and compared. The code that calculates the current for bare and partly insulated tethers with circular (wire) and rectangle (tape) cross-sections is presented. It takes into account the corrections to the OML current due to the tether cross-section geometry and the magnetic field produced by the tether current. There are two options in this code: for current calculation with the prescribed energy supply and with the prescribed end-point potential. This permits us to calculate the parameters characterizing tether performance. Results for the current calculated for tethers with different designs for the currently proposed Momentum exchange Electrodynamic Reboost (MXER) Tether System are presented.
Khazanov, G. V.↗
Operations analysis of gravity assisted rapid transit
Gravity assisted rapid transit (GART) with 6 percent grades before and after each station are compared with conventional systems in terms of energy consumption, run time, line capacity and schedule stability under abnormal circumstances. Parametric analyses of run times and energy consumption include the impact of alternate accelerating and braking levels. The capcity analysis uses a network simulation program to determine the location and severity of all signal delays. Based on results of initial simulations, the block design was revised to eliminate bottlenecks in normal operations. The systems are then compared at headways of 80 to 180 seconds. One month of incidence reports of a modern operating transit system are reviewed to determine the failures to be simulated. The impact of failures resulting in station delays (30 to 360 seconds), speed limit reduction (20 mph and 30 mph to one or more trains), vehicle performance (75 percent acceleration) are compared at scheduled headway of 90 to 180 seconds.
Source record↗
High performance dash on warning air mobile, missile system
An aircraft-missile system which performs a high acceleration takeoff followed by a supersonic dash to a 'safe' distance from the launch site is presented. Topics considered are: (1) technological feasibility to the dash on warning concept; (2) aircraft and boost trajectory requirements; and (3) partial cost estimates for a fleet of aircraft which provide 200 missiles on airborne alert. Various aircraft boost propulsion systems were studied such as an unstaged cryogenic rocket, an unstaged storable liquid, and a solid rocket staged system. Various wing planforms were also studied. Vehicle gross weights are given. The results indicate that the dash on warning concept will meet expected performance criteria, and can be implemented using existing technology, such as all-aluminum aircraft and existing high-bypass-ratio turbofan engines.
Levin, A. D.↗
Standardizing Microprocessor and GPU Radiation Test Approaches
Microprocessor, Graphics Processing Units (GPUs) and DDRx memory devices have emerged as promising next-generation technologies that enables both high performance processing and acceleration of complex algorithms for the latest challenges in human spaceflight, autonomous vehicles and artificial intelligence (AI). The feature sets of these devices offer exponential increases to throughput, calculation capability and system autonomy when compared to legacy flight systems. NASA's Electronic Part and Packaging (NEPP) Program has conducted an investigation into the radiation susceptibility of leading edge devices and process technologies by establishing standardized test approaches. Unlike most discrete devices, these require state of the art test systems to induce specific hardware activity similar to application software, thus allowing the characterization of failure modes within the system. To best characterize the tested part, NEPP eliminates variables that may impact device performance under radiation. Simplification of remaining system-level variables leads to an improved understanding of complex computational devices and their intended applications. The failure modes and error signatures that are recorded during testing are used to determine radiation sensitivity of the semiconductor process and the microcode architecture of the design. This presentation will discuss the test methodology that NASA Electronic Parts and Packaging (NEPP) is working to establish for its microprocessor, GPU and DDRx memory test programs to provide guidance on these devices and their underlying technology, in regards to their potential usage in future space flight systems.
GPU↗
Kinetic parameters from thermogravimetric analysis
High performance polymeric materials are finding increased use in aerospace applications. Proposed high speed aircraft will require materials to withstand high temperatures in an oxidative atmosphere for long periods of time. It is essential that accurate estimates be made of the performance of these materials at the given conditions of temperature and time. Temperatures of 350 F (177 C) and times of 60,000 to 100,000 hours are anticipated. In order to survey a large number of high performance polymeric materials on a reasonable time scale, some form of accelerated testing must be performed. A knowledge of the rate of a process can be used to predict the lifetime of that process. Thermogravimetric analysis (TGA) has frequently been used to determine kinetic information for degradation reactions in polymeric materials. Flynn and Wall studied a number of methods for using TGA experiments to determine kinetic information in polymer reactions. Kinetic parameters, such as the apparent activation energy and the frequency factor, can be determined in such experiments. Recently, researchers at the McDonnell Douglas Research Laboratory suggested that a graph of the logarithm of the frequency factor against the apparent activation energy can be used to predict long-term thermo-oxidative stability for polymeric materials. Such a graph has been called a kinetic map. In this study, thermogravimetric analyses were performed in air to study the thermo-oxidative degradation of several high performance polymers and to plot their kinetic parameters on a kinetic map.
Kiefer, Richard L.↗