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All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Experimental studies of transpiration cooling with shock interaction in hypersonic flow, part B

This report describes the result of experimental studies conducted to examine the effects of the impingement of an oblique shock on the flowfield and surface characteristics of a transpiration-cooled wall in turbulent hypersonic flow. The principal objective of this work was to determine whether the interaction between the oblique shock and the low-momentum region of the transpiration-cooled boundary layer created a highly distorted flowfield and resulted in a significant reduction in the cooling effectiveness of the transpiration-cooled surface. As a part of this program, we also sought to determine the effectiveness of transpiration cooling with nitrogen and helium injectants for a wide range of blowing rates under constant-pressure conditions in the absence of shock interaction. This experimental program was conducted in the Calspan 48-Inch Shock Tunnel at nominal Mach numbers of 6 and 8, for a Reynolds number of 7.5 x 10(exp 6). For these test conditions, we obtained fully turbulent boundary layers upstream of the interaction regions over the transpiration-cooled segment of the flat plate. The experimental program was conducted in two phases. In the first phase, we examined the effects of mass-addition level and coolant properties on the cooling effectiveness of transpiration-cooled surfaces in the absence of shock interaction. In the second phase of the program, we examined the effects of oblique shock impingement on the flowfield and surface characteristics of a transpiration-cooled surface. The studies were conducted for a range of shock strengths with nitrogen and helium coolants to examine how the distribution of heat transfer and pressure and the characteristics of the flowfield in the interaction region varied with shock strength and the level of mass addition from the transpiration-cooled section of the model. The effects of the distribution of the blowing rate along the interaction regions were also examined for a range of blowing rates through the transpiration-cooled panels. The regions of shockwave/boundary layer interaction examined in these studies were induced by oblique shocks generated with a sharp, flat plate, inclined to the freestream at angles of 5 degrees, 7.5 degrees, and 10 degrees. It was found that, in the absence of an incident shock, transpiration cooling was a very effective method for reducing both the heat transfer and the skin friction loads on the surface. The helium coolant was found to be significantly more effective than nitrogen, because of its low molecular weight and high specific heat. The studies of shock-wave/transpiration-cooled surface interaction demonstrated that the interaction region between the incident shock and the low-momentum transpiration-cooled boundary layer did not result in a significant increase in the size of attached or separated interaction regions, and did not result in significant flowfield distortions above the interaction region. The increase in heating downstream of the shock-impingement point could easily be reduced to the values without shock impingement by a relatively small increase in the transpiration cooling in this region. Surprisingly, this increase in cooling rate did not result in a significant increase in size of the region ahead of the incident shock or create a significantly enlarged interaction region with a resultant increase in the distortion level in the inviscid flow. Thus, transpiration cooling appears to be a very effective technique to cool the internal surfaces of scramjet engines, where shocks in the engine would induce large local increases in wall heating and create viscous/inviscid interactions that could significantly disturb the smooth flow through the combustor. However, if hydrogen is used as the coolant, burning upstream of shock impingement might result in localized hot spots. Clearly, further research is needed in this area.

Holden, Michael S.↗
NASA NTRS1993

Cost and schedule estimation study report

This report describes the analysis performed and the findings of a study of the software development cost and schedule estimation models used by the Flight Dynamics Division (FDD), Goddard Space Flight Center. The study analyzes typical FDD projects, focusing primarily on those developed since 1982. The study reconfirms the standard SEL effort estimation model that is based on size adjusted for reuse; however, guidelines for the productivity and growth parameters in the baseline effort model have been updated. The study also produced a schedule prediction model based on empirical data that varies depending on application type. Models for the distribution of effort and schedule by life-cycle phase are also presented. Finally, this report explains how to use these models to plan SEL projects.

Condon, Steve↗
NASA NTRS1993

Recent SEL experiments and studies

The studies discussed in this paper are all examples of activities that are performed as part of the Software Engineering Laboratory's (SEL's) process improvement model. Using this model, the SEL starts by understanding the product and process, then assesses the impact of new technologies, and finally packages what was learned. The preliminary examination of maintenance effort, error, and change profiles to establish a maintenance baseline exemplifies understanding-phase activities. The ongoing testing study that is examining the effects of various testing approaches on process and product measures is an example of typical assessing efforts. Finally, the derivation of cost and schedule estimation models from locally driven factors such as reuse level, application type, and language is an example of experience packaging. In the SEL, no study is ever really completed. Studies will be repeated and iterated upon in the future as part of the ongoing software improvement process.

Pajerski, Rose↗
NASA NTRS1982

Ellipsometric studies of sputtered silicon nitride on n-GaAs

Ellipsometry, which is the study of optical systems through their effect on polarized light, is a nondestructive technique offering extremely high sensitivity and in situ operation. One of the intriguing possibilities is to make use of the high sensitivity of ellipsometry for studying the very thin interface between an insulating film and a semiconductor substrate. Researchers have been especially interested in native or anodic oxides. In a recent study, Aspnes and Theeten used ellipsometry to study the interface between silicon and its thermally grown oxide, SiO2. These authors were able to conclude that the interface consisted of a 7 +/- 2 A graded region of atomically mixed silicon and oxygen. In this paper we report both analysis and experimental results for the system: sputtered silicon nitride on (100) n-type gallium arsenide.

Peng, Y. K.↗
NASA NTRS1994

Simulation study of the ROMPS robot control system

This is a report presenting the progress of a research grant funded by NASA for work performed from June 1, 1993 to August 1, 1993. The report deals with the Robot Operated Material Processing System (ROMPS). It presents results of a computer simulation study conducted to investigate the performance of the control systems controlling the azimuth, elevation, and radial axes of the ROMPS and its gripper. Four study cases are conducted. The first case investigates the control of free motion of the three areas. In the second case, the compliant motion in the elevation axis with the wrist compliant device is studied in terms of position accuracy and impact forces. The third case focuses on the behavior of the control system in controlling the robot motion along the radial axis when pulling the pallet out of the rack. In the fourth case, the compliant motion of the gripper grasping a solid object under the effect of the gripper passive compliance is studied in terms of position accuracy and contact forces. For each of the above cases, a set of PIR gains will be selected to optimize the controller performance and computer simulation results will be presented and discussed.

Nguyen, Charles C.↗
NASA NTRS1994

SeaWiFS technical report series. Volume 19: Case studies for SeaWiFS calibration and validation, part 2

This document provides brief reports, or case studies, on a number of investigations and data set development activities sponsored by the Calibration and Validation Team (CVT) within the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Project. Chapter 1 is a comparison with the atmospheric correction of Coastal Zone Color Scanner (CZCS) data using two independent radiative transfer formulations. Chapter 2 is a study on lunar reflectance at the SeaWiFS wavelengths which was useful in establishing the SeaWiFS lunar gain. Chapter 3 reports the results of the first ground-based solar calibration of the SeaWiFS instrument. The experiment was repeated in the fall of 1993 after the instrument was modified to reduce stray light; the results from the second experiment will be provided in the next case studies volume. Chapter 4 is a laboratory experiment using trap detectors which may be useful tools in the calibration round-robin program. Chapter 5 is the original data format evaluation study conducted in 1992 which outlines the technical criteria used in considering three candidate formats, the hierarchical data format (HDF), the common data format (CDF), and the network CDF (netCDF). Chapter 6 summarizes the meteorological data sets accumulated during the first three years of CZCS operation which are being used for initial testing of the operational SeaWiFS algorithms and systems and would be used during a second global processing of the CZCS data set. Chapter 7 describes how near-real time surface meteorological and total ozone data required for the atmospheric correction algorithm will be retrieved and processed. Finally, Chapter 8 is a comparison of surface wind products from various operational meteorological centers and field observations. Surface winds are used in the atmospheric correction scheme to estimate glint and foam radiances.

Hooker, Stanford B.↗
NASA NTRS1994

Trade study plan for Reusable Hydrogen Composite Tank System (RHCTS)

This TA 1 document describes the trade study plan (with support from TA 2) that will identify the most suitable structural configuration for an SSTO winged vehicle capable of delivering 25,000 lbs to a 220 nm circular orbit at 51.6 degree inclination. The analysis uses information derived in the TA 2 study as identified within the study plan. In view of this, for convenience, the TA 2 study plan is included as an appendix to this document.

Greenberg, H. S.↗
NASA NTRS1994

Proceedings of the Eighteenth NASA Propagation Experimenters Meeting (NAPEX 18) and the Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop

The NASA Propagation Experimenters Meeting (NAPEX), supported by the NASA Propagation Program, is convened annually to discuss studies made on radio wave propagation by investigators from domestic and international organizations. Participants included representatives from Canada, the Netherlands, England, and the United States, including researchers from universities, government agencies, and private industry. The meeting was organized into two technical sessions. The first session was dedicated to slant path propagation studies and experiments. The second session focused on propagation studies for mobile, personal, and sound broadcast systems. In total, 14 technical papers and some informal contributions were presented. Preceding NAPEX_17, the Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop was held to review ACTS propagation activities.

Davarian, Faramaz↗
NASA NTRS1994

An in-home study of subjective response to simulated sonic booms

The proposed development of a second-generation supersonic commercial transport has resulted in increased research efforts to provide an environmentally acceptable aircraft. One of the environmental issues is the impact of sonic booms on people. Aircraft designers are attempting to design the transport to produce sonic boom signatures that will have minimum impact on the public. Current supersonic commercial aircraft produce an 'N-wave' sonic boom pressure signature that is considered unacceptable by the public. This has resulted in first-generation supersonic transports being banned from flying supersonically over land in the United States, a severe economic constraint. By tailoring aircraft volume and lift distributions, designers hope to produce sonic boom signatures having specific shapes other than 'N-wave' that may be more acceptable to the public and could possibly permit overland supersonic flight. As part of the effort to develop a second-generation supersonic commercial transport, Langley Research Center is conducting research to study people's subjective response to sonic booms. As part of that research, a system was developed for performing studies of the subjective response of people to the occurrence of simulated sonic booms in their homes. The In-Home Noise Generation/Response System (IHONORS) provides a degree of situational realism not available in the laboratory and a degree of control over the noise exposure not found in community surveys. The computer-controlled audio system generates the simulated sonic booms, measures the noise levels, and records the subjects' rating and can be placed and operated in individuals' homes for extended periods of time. The system was used to conduct an in-home study of subjective response to simulated sonic booms. The primary objective of the study was to determine the effect on annoyance of the number of sonic boom occurrences in a realistic environment.

Mccurdy, David A.↗
NASA NTRS1994

Mars power system concept definition study. Volume 2: Appendices

This report documents the work performed by Rockwell International's Rocketdyne Division on NASA Contract No. NAS3-25808 (Task Order No. 16) entitled 'Mars Power System Definition Study'. This work was performed for NASA's Lewis Research Center (LeRC). The report is divided into two volumes as follows: Volume 1 - Study Results; and Volume 2 - Appendices. The results of the power system characterization studies, operations studies, and technology evaluations are summarized in Volume 1. The appendices include complete, standalone technology development plans for each candidate power system that was investigated.

Littman, Franklin D.↗
NASA NTRS1994

Space observations for global and regional studies of the biosphere

The capability to make space-based measurements of Earth at high spatial and temporal resolutions, which would not otherwise be economically or practically feasible, became available just in time to contribute to scientific understanding of the interactive processes governing the total Earth system. Such understanding has now become essential in order to take practical steps which would counteract or mitigate the pervasive impact of the growing human population on the future habitability of the Earth. The paper reviews the rationale for using space observations for studies of climate and terrestrial ecosystems at global and regional scales, as well as the requirements for such observations for studies of climate and ecosystem dynamics. The present status of these developments is reported along with initiatives under way to advance the use of satellite observations for Earth system studies. The most important contribution of space observations is the provision of physical or biophysical parameters for models representing various components of the Earth system. Examples of such parameters are given for climatic and ecosystem studies.

Cihlar, J.↗
NASA NTRS1995

Study of the space environmental effects on spacecraft engineering materials

The space environment in which the Space Station Freedom and other space platforms will orbit is truly a hostile environment. For example, the current estimates of the integral fluence for electrons above 1 Mev at 2000 nautical miles is above 2 x 10(exp 10) electrons/sq cm/day. and the proton integral fluence is above 1 x 109 protons/sq cm/day. At the 200 - 400 nautical miles, which is more representative of the altitude which will provide the environment for the Space Station, each of these fluences will be proportionately less; however, the data indicates that the radiation environment will obviously have an effect on structural materials exposed to the environment for long durations. The effects of this combined environment is the issue which needs to be understood for the long term exposure of structures in space. In order to better understand the effect of these hostile phenomena on spacecraft, several types of studies are worth performing in order to simulate at some level the effect of the environment. For example the effect of protons and electrons impacting structural materials are easily simulated through experiments using the Van de Graff and Pelletron accelerators currently housed in the Environmental Effects Facility at MSFC. Proton fluxes with energies of 700 Kev-2.5 Mev can be generated and used to impinge on sample targets to determine the effects of the particles. Also the Environmental Effects Facility has the capability to generate electron beams with energies from 700 Kev to 2.5 Mev. These facilities will be used in this research to simulate space environmental effects from energetic particles. Ultraviolet radiation, particularly in the ultraviolet (less than 400 nm wavelength) is less well characterized at this time. The Environmental Effects Facility has a vacuum system dedicated to studying the effects of ultraviolet radiation on specific surface materials. This particular system was assembled in a previous study (NAS8-38609) in order to perform a variety of experiments on materials proposed for the Space Station. That system has continued to function as planned and has been used in carrying out portions of the proposed study.

Obrien, Susan K.↗
NASA NTRS1995

Boundary layer transition studies

A small-scale wind tunnel previously used for turbulent boundary layer experiments was modified for two sets of boundary layer transition studies. The first study concerns a laminar separation/turbulent reattachment. The pressure gradient and unit Reynolds number are the same as the fully turbulent flow of Spalart and Watmuff. Without the trip wire, a laminar layer asymptotes to a Falkner & Skan similarity solution in the FPG. Application of the APG causes the layer to separate and a highly turbulent and approximately 2D mean flow reattachment occurs downstream. In an effort to gain some physical insight into the flow processes a small impulsive disturbance was introduced at the C(sub p) minimum. The facility is totally automated and phase-averaged data are measured on a point-by-point basis using unprecedently large grids. The evolution of the disturbance has been tracked all the way into the reattachment region and beyond into the fully turbulent boundary layer. At first, the amplitude decays exponentially with streamwise distance in the APG region, where the layer remains attached, i.e. the layer is viscously stable. After separation, the rate of decay slows, and a point of minimum amplitude is reached where the contours of the wave packet exhibit dispersive characteristics. From this point, exponential growth of the amplitude of the disturbance is observed in the detached shear layer, i.e. the dominant instability mechanism is inviscid. A group of large-scale 3D vortex loops emerges in the vicinity of the reattachment. Remarkably, the second loop retains its identify far downstream in the turbulent boundary layer. The results provide a level of detail usually associated with CFD. Substantial modifications were made to the facility for the second study concerning disturbances generated by Suction Holes for laminar flow Control (LFC). The test section incorporates suction through interchangeable porous test surfaces. Detailed studies have been made using isolated holes in the impervious test plate that used to establish the Blasius base flow. The suction is perturbed harmonically and data are averaged on the basis of the phase of the disturbance, for conditions corresponding to strong suction and without suction. The technique was enhanced by using up to nine multiple probes to reduce the experimental run-time. In both cases, 3D contour surfaces in the vicinity of the hole show highly 3D TS waves which fan out in the spanwise direction forming bow-shaped waves downstream. The case without suction has proved useful for evaluating calculation methods. With suction, the perturbations on the centerline are much stronger and decay less rapidly, while the TS waves in the far field are similar to the case without suction. Downstream, the contour surfaces of the TS waves develop spanwise irregularities which eventually form into clumps. The spanwise clumping is evidence of a secondary instability that could be associated with suction vortices. Designers of porous surfaces use Goldsmith's Criterion to minimize cross-stream interactions. It is shown that partial TS wave cancellation is possible, depending on the hole spacing, disturbance frequency and free-stream velocity. New high-performance Constant Temperature Hot-Wire Anemometers were designed and built, based on a linear system theory analysis that can be extended to arbitrary order. The motivation was to achieve the highest possible frequency reponse while ensuring overall system stability. The performance is equal to or superior to commercially available instruments at about 10% of the cost. Details, such as fabrication drawings and a parts list, have been published to enable the instrument to be construced by others.

Watmuff, Jonathan H.↗
NASA NTRS1995

Study of the space environmental effects on spacecraft engineering materials

The issue of the effects of the space environment on spacecraft needs to be understood for the long term exposure of structures in space. In order to better understand the effect of these hostile phenomena on spacecraft, several types of studies are worth performing in order to simulate at some level the effect of the environment. For example the effect of protons and electrons impacting structural materials are easily simulated through experiments using the Van de Graff and Pelletron accelerators currently housed at MSFC. Proton fluxes with energies of 700 KeV - 2.5 MeV can be generated and used to impinge on sample targets to determine the effects of the particles. Also the Environmental Effects Facility at MSFC has the capability to generate electron beams with energies from 700 KeV to 2.5 MeV. These facilities will be used in this research to simulate space environmental effects from energetic particles. Ultraviolet radiation, particularly less than 400 nm wavelength, is less well characterized at this time. The Environmental Effects Facility has a vacuum system dedicated to studying the effects of ultraviolet radiation on specific surface materials. This particular system was assembled in a previous study in order to perform a variety of experiments on materials proposed for the Space Station. That system has continued to function as planned and has been used in carrying out portions of the proposed study.

Obrien, Susan K.↗
NASA NTRS1995

A Fundamental Study of Smoldering with Emphasis on Experimental Design for Zero-G

A research program to study smoldering combustion with emphasis on the design of an experiment to be conducted in the space shuttle was conducted at the Department of Mechanical Engineering, University of California, Berkeley. The motivation of the research is the interest in smoldering both as a fundamental combustion problem and as a serious fire risk. Research conducted included theoretical and experimental studies that have brought considerable new information about smolder combustion, the effect that buoyancy has on the process, and specific information for the design of a space experiment. Experiments were conducted at normal gravity, in opposed and forward mode of propagation and in the upward and downward direction to determine the effect and range of influence of gravity on smolder. Experiments were also conducted in microgravity, in a drop tower and in parabolic aircraft flights, where the brief microgravity periods were used to analyze transient aspects of the problem. Significant progress was made on the study of one-dimensional smolder, particularly in the opposed-flow configuration. These studies provided enough information to design a small-scale space-based experiment that was successfully conducted in the Spacelab Glovebox in the June 1992 USML-1/STS-50 mission of the Space Shuttle Columbia.

Fernandez-Pello, Carlos↗
NASA NTRS1995

Preliminary study of Kelso Dunes using AVIRIS, TM, and AIRSAR

Remote sensing of sand dunes helps in the understanding of aeolian process and provides important information about the regional geologic history, environmental change, and desertification. Remotely sensed data combined with field studies are valuable in studying dune morphology, regional aeolian dynamics, and aeolian depositional history. In particular, active and inactive sands of the Kelso Dunes have been studied using landsat TM and AIRSAR. In this report, we describe the use of AVIRIS data to study the Kelso dunes and to compare the AVIRIS information with that from TM and AIRSAR.

Xu, Pung↗
NASA NTRS1994

An X-ray study of five supernova remnants in the Carina spiral arm

The ROSAT Position Sensitive Proportional Counter (PSPC) is used to perform an exploratory study of four fields in the Carina spiral arm containing five radio supernova remnants, only one of which has previously been studied in X-rays. We present upper limits for the detection in X-rays of G298.5 - 0.3, G298.6 - 0.0, and G299.0+0.2, and report a 4 sigma detection of G296.8-0.3. In addition, we present detailed spatial and spectral analysis of the bright X-ray remnant G296.1-0.7, which has previously been studied by both the Einstein IPC and EXOSAT LE/CMA. We detect relatively slight, but statistically significant, variations in the spectrum across the remnant via spatially resolved spectral fits and a study of the spatial variation of hardness ratios. In general, the spectrum is characteristic of a thermal plasma with kT about 0.2 keV and N(sub H) about 1.5 x 10(exp 21/sq. cm). The total X-ray emitting mass is estimated to be about 250 solar mass for an optically estimated distance of 4 kpc to the remnant. At this distance, the linear dimensions of the remnant are roughly 35 - 50 pc, implying an age on the order of 20,000 yr. Assuming that X-ray and radio brightnesses are related by SIGMA(sub R) proportional to SIGMA(exp 0.69)(sub X) and that the four radio remnants have X-ray spectral characteristics similar to G296.1-0.7, we find that the column densities to these sources must be several times 10(exp 22)/sq cm in order to explain their low X-ray count rates. This column density is considerably in excess of the X-ray fitted column density to G296.1-0.7, but is comparable to the total column densities in H I measured via the 21 cm line in the directions to all five remnants. This implies that G296.1 - 0.7 is at a significantly smaller distance than the other remnants.

Hwang, Una↗
NASA NTRS1993

A general circulation model study of the effects of faster rotation rate, enhanced CO2 concentration, and reduced solar forcing: Implications for the faint young sun paradox

Solar energy at the top of the atmosphere (solar constant), rotation rate, and carbon dioxide (CO2) may have varied significantly over Earth's history, especially during the earliest times. The sensitivity of a general circulation model to faster rotation, enhanced CO2 concentration, and reduced solar constant is presented. The control simulation of this study has a solar constant reduced by 10% the present amount, zero land fraction using a swamp ocean surface, CO2 concentrations of 330 ppmv, present-day rotation rate, and is integrated under mean diurnal and seasonal solar forcing. Four sensitivity test are performed under zero land fraction and reduced solar constant conditions by varying the earth's rotation rate atmospheric CO2 concentration and solar constant. The global mean sea surface temperatures (SSTs) compared to the control simulation: were 6.6 K to 12 K higher than the control's global mean temperature of 264.7 K. Sea ice is confined to higher latitudes in each experiment compared to the control, with ice-free areas equatorward of the subtropics. The warm SSTs are associated with a 20% reduction in clouds for the rotation rate experiments and higher CO2 concentrations in the other experiments. These results are in contrast to previous studies that have used energy balance and radiative convective models. Previous studies required a much larger atmospheric CO2 increase to prevent an ice-covered Earth. The results of the study, suggest that because of its possible feedback with clouds, the general circulation of the atmosphere should be taken into account in understanding the climate of early Earth. While higher CO2 concentrations are likely in view of the results, very large atmospheric CO2 concentrations may not be necessary to counterbalance the lower solar constant that existed early in Earth's history.

Jenkins, Gregory S.↗