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At least 811 records · Page 45

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NASA NTRSDate not supplied

Validation of a Multiphase Computational Fluid Dynamics Model for Vapor Pull-Through in Normal and Low Gravity

On-orbit fluid transfer such as refueling of propellant tanks and life-support systems can enable long-duration space missions. For safe and efficient liquid transfer operations, prior knowledge of liquid positioning and liquid-vapor interface behavior while draining in a low-gravity environment is required. Numerical models capable of predicting vapor ingestion (or vapor pull-through) can be used to design liquid transfer operations while reducing liquid residuals, mission risk and settling thrust required to prevent vapor ingestion. An experimental program conducted in the 2.2 Second Drop Tower facility at NASA Glenn Research Center investigated the vapor ingestion phenomenon for a range of outflow rates and tank sizes providing a database for validation. This study presents a Computational Fluid Dynamics model capable of accurately predicting the vapor ingestion using the Volume-of-Fluid multiphase solver in commercial code STAR-CCM+. A description of the experimental setup and general trends from similar studies are presented. Comparisons of the numerical prediction and test data in normal and low gravity show good agreement and give confidence in pursuing design of full-scale propellant transfer systems.

Computational Fluid Dynamics↗

NASA NTRSDate not supplied

Validation of a Multiphase Computational Fluid Dynamics Model for Vapor Pull-Through in Normal and Low Gravity

On-orbit fluid transfer such as refueling of propellant tanks and life-support systems can enable long-duration space missions. For safe and efficient liquid transfer operations, prior knowledge of liquid positioning and liquid-vapor interface behavior while draining in a reduced-gravity environment is required. Numerical models capable of predicting vapor ingestion (or vapor pull-through) can be used to design liquid transfer operations while reducing liquid residuals, mission risk and settling thrust required to prevent vapor ingestion. An experimental program conducted in the 2.2 Second Drop Tower facility at NASA Lewis Research Center in 1969 investigated the vapor ingestion phenomenon for a range of outflow rates and tank sizes providing a database for validation. This study presents a Computational Fluid Dynamics model capable of accurately predicting the vapor ingestion using the Volume-of-Fluid multiphase solver in commercial code STAR-CCM+. A description of the experimental setup and general trends from similar studies are presented. Comparisons of the numerical prediction and test data in normal and low gravity show good agreement and give confidence in pursuing design of full-scale propellant transfer systems.

Computational Fluid Dynamics↗

NASA NTRSDate not supplied

Validation of A Multiphase Computational Fluid Dynamics Model for Vapor Pull-Through in Normal and Low Gravity

On-orbit fluid transfer such as refueling of propellant tanks and life-support systems can enable long-duration space missions. For safe and efficient liquid transfer operations, prior knowledge of liquid positioning and liquid-vapor interface behavior while draining in a reduced-gravity environment is required. Numerical models capable of predicting vapor ingestion (or vapor pull-through) can be used to design liquid transfer operations while reducing liquid residuals, mission risk and settling thrust required to prevent vapor ingestion. An experimental program conducted in the 2.2 Second Drop Tower facility at NASA Lewis Research Center in 1969 investigated the vapor ingestion phenomenon for a range of outflow rates and tank sizes providing a database for validation. This study presents a Computational Fluid Dynamics model capable of accurately predicting the vapor ingestion using the Volume-of-Fluid multiphase solver in commercial code STAR-CCM+. A description of the experimental setup and general trends from similar studies are presented. Comparisons of the numerical prediction and test data in normal and low gravity show good agreement and give confidence in pursuing design of full-scale propellant transfer systems.

Propellant Transfer↗

NASA NTRS2014

A New Global Regression Analysis Method for the Prediction of Wind Tunnel Model Weight Corrections

A new global regression analysis method is discussed that predicts wind tunnel model weight corrections for strain-gage balance loads during a wind tunnel test. The method determines corrections by combining "wind-on" model attitude measurements with least squares estimates of the model weight and center of gravity coordinates that are obtained from "wind-off" data points. The method treats the least squares fit of the model weight separate from the fit of the center of gravity coordinates. Therefore, it performs two fits of "wind- off" data points and uses the least squares estimator of the model weight as an input for the fit of the center of gravity coordinates. Explicit equations for the least squares estimators of the weight and center of gravity coordinates are derived that simplify the implementation of the method in the data system software of a wind tunnel. In addition, recommendations for sets of "wind-off" data points are made that take typical model support system constraints into account. Explicit equations of the confidence intervals on the model weight and center of gravity coordinates and two different error analyses of the model weight prediction are also discussed in the appendices of the paper.

strain-gage balance↗

NASA NTRS1986

Orbit determination using dual crossing arc altimetry

Accurate knowledge of the position of an altimetric satellite is required for the altimeter range data to be effective in measuring ocean topography. This study addresses the use of high-precision altimeter data from NASA's TOPEX Mission in reducing the radial component of the orbit of the U.S. Navy's N-ROSS satellite. Simulated altimeter crossing arc residuals between the TOPEX and N-ROSS orbits are minimized using both geometric and dynamic techniques in an effort to reduce the N-ROSS radial error to a level comparable to that of TOPEX. Tracking of N-ROSS by the Navy's NAVSPASUR system is simulated, and crossover residuals are created from the TOPEX and N-ROSS orbits. A simple geometric fit is shown to reduce the radial component of the NAVSPASUR N-ROSS orbit error from 350 m RMS to below 10 m RMS. In comparison, the dynamic approach of estimating the initial conditions of the N-ROSS orbit using a twentieth degree and order gravity field and a combined data set of tracking and altimeter crossover data yields a 6 m RMS residual error. Sub-meter accuracy can be attained by geometrically fitting these residuals to remove long wavelength orbit error.

Born, G. H.↗

NASA NTRS1984

Detection of Solar Gravity Mode Oscillations

An analysis of solar velocity data obtained at the Stanford Solar Observatory has shown the existence of solar global oscillations. The oscillations are in the range 45 to 105 micro Hz (160 to 370 minutes) and are interpreted as internal gravity modes of degree l=1 and l=2.

Scherrer, P. H.↗

NASA NTRS1992

A microwave holography methodology for diagnostics and performance improvement for large reflector antennas

This microwave holography technique utilizes the Fourier transform relation between the complex far field radiation pattern of an antenna and the complex aperture field distribution. Resulting aperture phase and amplitude distribution data can be used to precisely characterize various crucial performance parameters, including panel alignment, panel shaping, subreflector position, antenna aperture illumination, directivity at various frequencies, and gravity deformation effects. The methodology of data processing presented here was successfully applied to the Deep Space Network (DSN) 34-m beam waveguide antennas. The antenna performance was improved at all operating frequencies by reducing the main reflector mechanical surface rms error to 0.43 mm. At Ka-band (32 GHz), the estimated improvement is 4.1 dB, resulting in an aperture efficiency of 52 percent. The performance improvement was verified by efficiency measurements and additional holographic measurements.

Rochblatt, D. J.↗

NASA NTRS1992

Microwave antenna holography

Rochblatt, David J.↗

NASA NTRS2007

Monitoring Immune System Function and Reactivation of Latent Viruses in the Artificial Gravity Pilot Study

Numerous studies have indicated that dysregulation of the immune system occurs during or after spaceflight. Using 21 day -6 deg. head-down tilt bed rest as a spaceflight analog, this study describes the effects of artificial gravity as a daily countermeasure on immunity, stress and reactivation of clinically important latent herpes viruses. The specific aims were to evaluate psychological and physiological stress, to determine the status of the immune system and to quantify reactivation of latent herpes viruses. Blood, saliva, and urine samples were collected from each participating subject at different times throughout the study. An immune assessment was performed on all treatment and control subjects that consisted of a comprehensive peripheral immunophenotype analysis, intracellular cytokine profiles and a measurement of T cell function. The treatment group displayed no differences throughout the course of the study with regards to peripheral leukocyte distribution, cytokine production or T cell function. Shedding of EBV and CMV was quantified by real time PCR in saliva and urine samples, respectively. There was no significant difference in CMV DNA in the treatment group as compared to the control group. EBV and VZV on the other hand showed a mild reactivation during the study. There were no significant differences in plasma cortisol between the control and treatment groups. In addition, no significant differences between antiviral antibody titers (EBV-VCA, -EA, -EBNA, CMV) or tetramer-positive (EBV, CMV) were found between the two groups. EBV DNA copies in blood were typically undetectable but never exceeded 1,500 copies per 10(exp 6) PBMCs. These data indicate that the artificial gravity countermeasure and the 21 day head-down tilt bed rest regimen had no observable adverse effect on immune function.

Mehta, Satish↗

NASA NTRS2007

Monitoring Immune System Function and Reactivation of Latent Viruses in the Artificial Gravity Pilot Study

Numerous studies have indicated that dysregulation of the immune system occurs during or after spaceflight. Using 21 day -6 degrees head-down tilt bed rest as a spaceflight analog, this study describes the effects of artificial gravity (AG) as a daily countermeasure on immunity, stress and reactivation of clinically important latent herpes viruses. The specific aims were to evaluate psychological and physiological stress, to determine the status of the immune system, and to quantify reactivation of latent herpes viruses. Blood, saliva, and urine samples were collected from each participating subject at different times throughout the study. An immune assessment was performed on all treatment and control subjects that consisted of a comprehensive peripheral immunophenotype analysis, intracellular cytokine profiles and a measurement of T cell function. The treatment group displayed no differences throughout the course of the study with regards to peripheral leukocyte distribution, cytokine production or T cell function. Shedding of Epstein barr virus (EBV), Cytomegalovirus (CMV), and Varicella zoster virus (VZV) was quantified by real time PCR in saliva and urine samples, respectively. There was no significant difference in CMV DNA in the treatment group as compared to the control group. EBV and VZV on the other hand showed a mild reactivation during the study. There were no significant differences in cortisol between the control and treatment groups. In addition, no significant differences between antiviral antibody titers (EBV-VCA, -EA, -EBNA, CMV) or tetramer-positive (EBV, CMV) were found between the two groups. EBV DNA copies in blood were typically undetectable but never exceeded 1,500 copies per 106 PBMCs. Overall, these data indicate that the artificial gravity countermeasure and the 21 day head-down tilt bed rest regimen had no observable adverse effect on immune function.

Mehta, Satish K.↗

NASA NTRS2001

Three-Dimensional Upward Flame Spreading in Partial-Gravity Buoyant Flows

Reduced-gravity environments have been used to establish low-speed, purely forced flows for both opposed- and concurrent-flow flame spread studies. Altenkirch's group obtained spacebased experimental results and developed unsteady, two-dimensional numerical simulations of opposed-flow flame spread including gas-phase radiation, primarily away from the flammability limit for thin fuels, but including observations of thick fuel quenching in quiescent environments. T'ien's group contributed some early flame spreading results for thin fuels both in opposed flow and concurrent flow regimes, with more focus on near-limit conditions. T'ien's group also developed two- and three-dimensional numerical simulations of concurrent-flow flame spread incorporating gas-phase radiative models, including predictions of a radiatively-induced quenching limit reached in very low-speed air flows. Radiative quenching has been subsequently observed in other studies of combustion in very low-speed flows including other flame spread investigations, droplet combustion and homogeneous diffusion flames, and is the subject of several contemporary studies reported in this workshop. Using NASA aircraft flying partial-gravity "parabolic" trajectories, flame spreading in purely buoyant, opposed-flow (downward burning) has been studied. These results indicated increases in flame spread rates and enhanced flammability (lower limiting atmospheric oxygen content) as gravity levels were reduced from normal Earth gravity, and were consistent with earlier data obtained by Altenkirch using a centrifuge. In this work, experimental results and a three-dimensional numerical simulation of upward flame spreading in variable partial-gravity environments were obtained including some effects of reduced pressure and variable sample width. The simulation provides physical insight for interpreting the experimental results and shows the intrinsic 3-D nature of buoyant, upward flame spreading. This study is intended to link the evolving understanding of flame spreading in purely-forced flows to the purely-buoyant flow environment, particularly in the concurrent flow regime; provide additional insight into the existence of steady flame spread in concurrent flows; and stimulate direct comparisons between opposed- and concurrent-flow flame spread. Additionally, this effort is intended to provide direct practical understanding applicable to fire protection planning for the habitable facilities in partial gravity environments of anticipated Lunar and Martian explorations.

Sacksteder, Kurt R.↗

NASA NTRS1983

Inference of variations in the gravity field from satellite-to-satellite range rate

An analytic scheme for inferring variations of the gravity field from satellite-to-satellite range rate (low-low) is developed. As a test, it is applied to a pair of satellites in polar orbit, at altitude 160 km and spacing 100 km, with 72 data points per revolution. An assumed gravity field of tesseral spherical harmonics up to the eighth degree is completely recovered in three iterations over 64 revolutions. It is apparent that data points at regular intervals enable the use of data analysis techniques that avoid massive matrix inversions.

Kaula, W. M.↗

NASA NTRS2009

The Effect of Center of Gravity and Anthropometrics on Human Performance in Simulated Lunar and Mars Gravity

Drawing from the experiences of the Apollo missions, it is evident that the off nominal center of gravity (CG) induced by the portable life support system (PLSS) had significant impact on the locomotion stability of the crew. This in turn is believed to have been a major contributor to the high numbers of falls and high metabolic rates experienced by the crew, and thus significantly hampered the crew s performance. With this in mind, the EVA Physiology, Systems and Performance (EPSP) group at the NASA Johnson Space Center (JSC) has been conducting tests to assess how spacesuit CG location impacts human performance in simulated lunar and Mars gravity. The results acquired to date show correlations between CG location and performance. However, noticeable variations in the performance data have been observed across subjects for fixed CG configurations. Consequently, it was hypothesized that this variability may be attributed to the anthropometrics of the different test subjects. It was further hypothesized that trunk-to-height ratio (THR) may be directly correlated to performance in reduced gravity; i.e. subjects with increased THR may have increased performance. To test this hypothesis, lunar and Mars gravity test data acquired over three years during NASA Neural Buoyancy Lab (NBL) tests and NASA Extreme Environment Missions Operation (NEEMO) missions were analyzed against THR, height, trunk length, and subject body mass/weight. The results of the study supported the hypothesis relating THR and performance, while the other three anthropometric parameters did not provide consistent correlations with performance. This in turn suggests that human performance in reduced gravity may be more dependent on anthropometric proportions than on body segment lengths and mass/weight.

Mulugeta, Lealem↗

NASA NTRS1999

The Measurement of Mars Rotation Rate and Pole Position with MGS

Laser altimeter data and microwave tracking of the MGS (Mars Global Surveyor) spacecraft have been used to estimate rotation parameters for Mars. With the recent development of new high resolution gravity models for Mars and the determination of the orbit of the MGS spacecraft to the few meter level it has become possible to obtain rotational information about the planet. Perturbations of the spacecraft orbit by the planet's gravity field permit the gravity field to be estimated from the tracking data. But the perturbations arising from the non-zonal components of the gravity field have a periodicity related to the rotation of Mars on its axis and these perturbations enable the rotation rate and direction of the rotation pole in inertial space to be measured with respect to the orbit of the spacecraft. It is the anomalies in the gravity field that permit these parameters to be obtained. Similarly, altimetry data are sensitive to errors in the orbital altitude at orbital cross-over locations and the locations themselves are a function of the rotation of the planet. Thus, altimetric measurements by MOLA provide a geometric constraint on the rotation of the planet through the timing of the orbital cross-over pattern as well as information that improves the orbit determination. For a few months in 1999 MGS tracking and altimetry data have been used in a preliminary experiment to estimate the rotation rate of Mars and the right ascension and declination of the pole from an orbiting spacecraft. These preliminary results appear to have sufficient accuracy to permit detection of seasonal changes in rotation rate and also precession of the pole thus leading to a possible eventual measurement of the moment of inertia.

Smith, David E.↗

NASA NTRS1976

The effect of remote zones on the accuracy of evaluating the Molodensky

An analytical method is presented for determining the error in computing the gravity anomaly from the Molodensky integral if geoidal undulation data in remote zones are neglected. The error is given in terms of the usual degree variance and a set of parameters which are functions only of the size of the area in which undulation data are taken. A numerical calculation using Kaula's degree variances indicates that it is necessary to integrate the Molodensky integral over approximately a hemisphere in order to reduce the effect of neglected data to the order of 1 milligal in the computation of gravity anomaly.

Buglia, J. J.↗

NASA NTRS1977

Gravitational harmonics from shallow resonant orbits

Gravitational constraint (lumped coefficient) equations are derived from GEOS-2 data and a detailed analysis of the shallow resonance problem. The equations follow from elementary perturbation theory and show that all such lumped coefficients are harmonic in the argument of perigee. The best along-track constraints derived from them account for all but about 2% of the 13th-order resonant information in the tracking data. The equations are also in good agreement with recent comprehensive gravity models which use substantial amounts of GEOS-2 data.

Wagner, C. A.↗

NASA NTRS1981

Forced and natural convection in laminar-jet diffusion flames

An experimental investigation was conducted on methane, laminar-jet, diffusion flames with coaxial, forced-air flow to examine flame shapes in zero-gravity and in situations where buoyancy aids (normal-gravity flames) or hinders (inverted-gravity flames) the flow velocities. Fuel nozzles ranged in size from 0.051 to 0.305 cm inside radius, while the coaxial, convergent, air nozzle had a 1.4 cm inside radius at the fuel exit plane. Fuel flows ranged from 1.55 to 10.3 cu cm/sec and air flows from 0 to 597 cu cm/sec. A computer program developed under a previous government contract was used to calculate the characteristic dimensions of normal and zero-gravity flames only. The results include a comparison between the experimental data and the computed axial flame lengths for normal gravity and zero gravity which showed good agreement. Inverted-gravity flame width was correlated with the ratio of fuel nozzle radius to average fuel velocity. Flame extinguishment upon entry into weightlessness was studied, and it was found that relatively low forced-air velocities (approximately 10 cm/sec) are sufficient to sustain methane flame combustion in zero gravity. Flame color is also discussed.

Haggard, J. B., Jr.↗

NASA NTRS1991

Heart-Lung Interactions in Aerospace Medicine

Few of the heart-lung interactions that are discussed have been studied in any detail in the aerospace environment, but is seems that many such interactions must occur in the setting of altered accelerative loadings and pressure breathing. That few investigations are in progress suggests that clinical and academic laboratory investigators and aerospace organizations are further apart than during the pioneering work on pressure breathing and acceleration tolerance in the 1940s. The purpose is to reintroduce some of the perennial problems of aviation physiology as well as some newer aerospace concerns that may be of interest. Many possible heart-lung interactions are pondered, by necessity often drawing on data from within the aviation field, collected before the modern understanding of these interactions developed, or on recent laboratory data that may not be strictly applicable. In the field of zero-gravity effects, speculation inevitably outruns the sparse available data.

Guy, Harold J. B.↗