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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Orion GN&C Detection and Mitigation of Parachute Pendulosity

New techniques being employed by Orion guidance, navigation, and control (GN&C) using a reaction control system (RCS) under parachutes are described. Pendulosity refers to a pendulum-oscillatory mode that can occur during descent under main parachutes and that has been observed during Orion parachute drop tests. The pendulum mode reduces the ability of GN&C to maneuver the suspended vehicle resulting in undesirable increases to structural loads at touchdown. Parachute redesign efforts have been unsuccessful in reducing the pendulous behavior necessitating GN&C mitigation options. An observer has been developed to estimate the pendulum motion as well as the underlying wind velocity vector. Using this knowledge, the control system maneuvers the vehicle using two separate strategies determined by wind velocity magnitude and pendulum energy thresholds; at high wind velocities the vehicle is aligned with the wind direction and for cases with lower wind velocities and large pendulum amplitudes the vehicle is aligned such that it is perpendicular to the swing plane. Pendulum damping techniques using RCS thrusters are discussed but have not been selected for use onboard the Orion spacecraft. The techniques discussed in this paper will be flown on Exploration Mission 1 (EM-1).

Kane, Mark A.↗
NASA NTRS1993

Microwave radiative transfer studies of precipitation

Since the deployment of the DMSP SSM/I microwave imagers in 1987, increased utilization of passive microwave radiometry throughout the 10 - 100 GHz spectrum has occurred for measurement of atmospheric constituents and terrestrial surfaces. Our efforts have focused on observations and analysis of the microwave radiative transfer behavior of precipitating clouds. We have focused particular attention on combining both aircraft and SSM/I radiometer imagery with ground-based multiparameter radar observations. As part of this and the past NASA contract, we have developed a multi-stream, polarized radiative transfer model which incorporates scattering. The model has the capability to be initialized with cloud model output or multiparameter radar products. This model provides the necessary 'link' between the passive microwave radiometer and active microwave radar observations. This unique arrangement has allowed the brightness temperatures (TB) to be compared against quantities such as rainfall, liquid/ice water paths, and the vertical structure of the cloud. Quantification of the amounts of ice and water in precipitating clouds is required for understanding of the global energy balance.

Bringi, V. N.↗
NASA NTRSDate not supplied

Plume-Surface Interaction: Preliminary Observations from a Physics Focused Ground Test

Near surface operations conducted by spacecraft using rocket propulsion, such as during landing or the initial portion of ascent, may induce surface interactions that pose a risk to the spacecraft itself or nearby assets. NASA’s Space Technology Mission Directorate is conducting a multi-year project to mature the capability to predict plume-surface interactions (PSI) and reduce uncertainty through modeling, simulation, and ground testing. The Physics Focused Ground Test (PFGT), conducted in summer 2021, aimed to collect PSI data for plume, erosion, and ejecta physics to characterize PSI behaviors across a range of parameters relevant to the validation of computational modeling and with consideration to flight-relevant, though not flight-scale, environments. PFGT is a sub-scale, intrusive half-plane, inert-gas test conducted in a 15 foot-diameter vacuum chamber using a supersonic, heated, gaseous nitrogen plume. Tests were conducted with six regolith simulants, varying in complexity from spherical glass beads to BP-1 lunar soil simulant, and varied vacuum chamber ambient pressures to simulate Martian and lunar conditions. Nozzle height and mass flow rate were also varied to observe PSI behaviors and transitions of interest. Three high speed cameras captured crater formation and ejecta behavior during each test. An overview of this experiment is presented along with preliminary observations and analysis.

Wesley A Chambers↗
NASA NTRS1987

Microwave dielectric spectrum of vegetation. I - Experimental observations. II - Dual-dispersion model

The microwave dielectric behavior of vegetation materials is examined as a function of water content, microwave frequency, and temperature. Dielectric spectra for various types of vegetation, such as leaves, stalks, and trunks at various moisture conditions, were measured using a coaxial probe technique. The basic features and operation of the coaxial probe system are described. Examples of dielectric measurements for the vegetation materials are presented, and the relation between temperature and the dielectric constant is studied. The development of a dual-dispersion model that accounts for the dielectric properties of water in both free and bound conditions is described. The applicability of the model is evaluated by comparing it with the dielectric data; good correlation is observed between the model and the data over a wide range of moisture conditions and over the 0.2-20 GHz range.

El-Rayes, Mohamed A.↗
NASA NTRS1976

The quiet sun in the extreme ultraviolet

Observations of the quiet sun with an XUV spectrometer during the Skylab mission are reported for the chromosphere, transition region, and corona. The changing structure of the network is examined over the temperature range from 10,000 to 1.5 million K, and the distribution of intensities in the cell interiors and the network are examined from the standpoint of creating characteristic models. Observations of traces of periodic oscillations at 300 s in the cells for temperatures not exceeding 20,000 K are reported together with the absence of any periodic contributions at higher temperatures or periodic effects at any height in the network elements. Frequent nonperiodic brightenings are observed, and their characteristics discussed. Observations of the increased thickness of the transition region in coronal holes, as well as other properties, are discussed in limited detail. Observations of the center-to-limb behavior of transition-region and coronal lines are used to construct coronal models, and the assumptions of spherical symmetry evaluated from the intensity data. The effects of spicules on the limb and disk data are discussed in relation to the observations.

Reeves, E. M.↗
NASA NTRS2016

Orion GN&C Detection and Mitigation of Parachute Pendulosity

New techniques being employed by Orion guidance, navigation, and control (GN&C) using a reaction control system (RCS) under parachutes are described. Pendulosity refers to a pendulum-oscillatory mode that can occur during descent under main parachutes and that has been observed during Orion parachute drop tests. The pendulum mode reduces the ability of GN&C to maneuver the suspended vehicle resulting in undesirable increases to structural loads at touch-down. Parachute redesign efforts have been unsuccessful in reducing the pendulous behavior necessitating GN&C mitigation options. An observer has been developed to estimate the pendulum motion as well as the underlying wind velocity vector. Using this knowledge the control system maneuvers the vehicle using two separate strategies determined by a wind velocity magnitude threshold; at high wind velocities the vehicle is aligned with the wind direction and for cases with lower wind velocities the vehicle is aligned such that it is perpendicular to the swing plane. Pendulum damping techniques using RCS thrusters are discussed but have not been selected for use onboard the Orion spacecraft. The techniques discussed in this paper will be flown on Exploration Mission 1 (EM-1).

Kane, Mark A.↗
NASA NTRS2001

Where to look? Automating attending behaviors of virtual human characters

This research proposes a computational framework for generating visual attending behavior in an embodied simulated human agent. Such behaviors directly control eye and head motions, and guide other actions such as locomotion and reach. The implementation of these concepts, referred to as the AVA, draws on empirical and qualitative observations known from psychology, human factors and computer vision. Deliberate behaviors, the analogs of scanpaths in visual psychology, compete with involuntary attention capture and lapses into idling or free viewing. Insights provided by implementing this framework are: a defined set of parameters that impact the observable effects of attention, a defined vocabulary of looking behaviors for certain motor and cognitive activity, a defined hierarchy of three levels of eye behavior (endogenous, exogenous and idling) and a proposed method of how these types interact.

NASA Discipline Space Human Factors↗
NASA NTRS1974

Some qualitative remarks on the variation of the probability of error

The qualitative behavior of the probability of misclassifying observations from two normally distributed populations as the classification regions are varied in a prescribed way is described in order to provide a preliminary generalization of the results obtained by Walton for the case of normally distributed observations with varying a priori probabilities.

Walker, H. F.↗
NASA NTRS1976

Vibrational spectra and structure of dimethyl oxalate and dimethyl oxalate-d6

The vibrational spectra of dimethyl oxalate-d6 have been examined in connection with a re-examination of the spectra and structure of dimethyl oxalate. The vibrational spectra of the compound had previously been interpreted as being consistent with a trans C2h structure in the solid phase and a non-planar C2 form in the liquid and gas phases. This behavior is not consistent with that observed in similar compounds and a re-evaluation of the facts suggests that the major spectral changes which are observed may be caused by destroying an intermolecular association in going from the solid to the liquid phase, which allows the methyl groups to assume positions out of the plane. Some modifications and additions have been made in the vibrational assignment and assignments are presented for the deuterated compound.

Durig, J. R.↗
NASA NTRS1978

Observations on instabilities of cavitating inducers

Experimental observations of instability of cavitating inducers were made for two different inducers operating at different flow coefficients. In general, instability occurred just before head breakdown. Auto-oscillation and rotating cavitation were observed. Analysis of small-amplitude behavior of the inducer and hydraulic system is carried out, and analytical predictions of stability limits were compared with experiment.

Braisted, D.↗
NASA NTRS1979

The HEAO-A2 soft X-ray survey of cataclysmic variable stars - EX Hydrae during optical quiescence

Results are reported for HEAO A2 soft X-ray (below 2 keV) scanning observations of the southern dwarf nova EX Hya. An X-ray light curve is presented which shows no apparent orbital modulation. The best-fitting spectral parameters are derived for the source, and the observations are compared with the spectral behavior of the dwarf nova SS Cyg during optical quiescence. The results are discussed in terms of models for X-ray production by accreting white dwarfs.

Cordova, F. A.↗
NASA NTRS1983

Noise of the SR-6 propeller model at 2 deg and 4 deg angles of attack

The noise generated by supersonic-tip-speed propellers creates a cabin noise problem for future airplanes powered by these propellers. Noise of a number of propeller models were measured in the NASA Lewis 8- by 6-Foot Wind Tunnel with flow parallel to the propeller axis. In flight, as a result of the induced upwash from the airplane wing, the propeller is at an angle of attack with respect to the incoming flow. Therefore, the 10-blade SR-6 propeller was operated at angle of attack to determine its noise behavior. Higher blade passage tones were observed for the propeller operating at angle of attack in a 0.6 axial Mach number flow. The noise increase was not symmetrical, with one wall of the wind tunnel showing a larger noise increase than the other wall. No noise increase was observed at angle of attack in a 0.8 axial Mach number flow. For this propeller the dominance of thickness noise, which does not increase with angle of attack, explains the lack of noise increase at the higher 0.8 Mach number.

Dittmar, J. H.↗
NASA NTRS1983

Consolidation of Si3N4 without additives (by hot isostatic pressing)

The potential of using hot isostatic pressing (HIP'ing) technique to produce dense silicon nitride materials without or with a reduced amount of additives (much less than 5 w/o) was investigated. Hot isostatic pressing technique can provide higher pressure and temperature than hot pressing can, thus has the potential of requiring less densification aids to consolidate Si3N4 materials. It was anticipated that if such dense materials could be fabricated, the high temperature strength of the material should be improved significantly. Observations on the phase transformation, densification behavior, and microstructures of the samples are also documented. Density, microhardness, four point bend strength (room temperature and 1370 C) were measured on selected densified materials.

Yeh, H. C.↗
NASA NTRS1984

Critical point wetting drop tower experiment

Preliminary results for the Critical Point Wetting CPW Drop Tower Experiment are produced with immiscible systems. Much of the observed phenomena conformed to the anticipated behavior. More drops will be needed to test the CPW theory with these immiscible systems.

Kaukler, W. F.↗
NASA NTRS1984

DE-1 observations of ordinary mode and extraordinary mode auroral kilometric radiation

Observations of auroral kilometric radiation (AKR) made with the Dynamics Explorer (DE-1) indicate the presence of both ordinary and extraordinary wave modes. Although the two modes usually occur separately, they are sometimes observed together. When both modes are present, the ordinary-mode component tends to occur at lower frequencies and with lower amplitudes than those of the accompanying extraordinary-mode component. On the other hand, the local electron gyrofrequency is an absolute lower frequency cutoff for both modes. Ordinary mode intensities are proportional to extraordinary mode intensities but less by roughly a factor of 50. Extraordinary mode ray paths are generally confined to a cone within 50 degrees of the source magnetic field direction and ordinary mode emissions are typically observed outside of this cone. This behavior suggests that both components are produced within the same source region but are then refracted differently as they escape.

Mellott, M. M.↗
NASA NTRS1985

Models of cometary emission in the 18-cm OH transitions - The predicted behavior of Comet Halley

The return of Halley's comet to the inner solar system in 1985-1986 presents an excellent opportunity to study the behavior of a bright comet, since observations may be planned ahead of time to yield the maximum scientific return. Observations of the OH radical in the 18-cm wavelength Alpha-doublet transitions can be expected to yield significant results to cometary science in a number of areas from the measurement of the production rate of OH parent molecules (water) to the elucidation of the kinematics in the coma. Therefore, models of the OH emission from the comae of comets are presented together with predictions of brightness and spectra of Halley's Comet during the current apparition as an aid to prospective observers. The desirability of certain observational programs, including monitoring, mapping, polarimetry, and occultation experiments, are also discussed.

Schloerb, F. P.↗
NASA NTRS1985

Normal mode Rossby waves observed in the upper stratosphere

In recent years, observational evidence has been obtained for westward traveling planetary waves in the middle atmosphere with the aid of global data from satellites. There is no doubt that the fair portion of the observed traveling waves can be understood as the manifestation of the normal mode Rossby waves which are theoretically derived from the tidal theory. Some observational aspects of the structure and behavior of the normal model Rossby waves in the upper stratosphere are reported. The data used are the global stratospheric geopotential thickness and height analyses which are derived mainly from the Stratospheric Sounding Units (SSUs) on board TIROS-N and NOAA satellites. A clear example of the influence of the normal mode Rossby wave on the mean flow is reported. The mechanism considered is interference between the normal mode Rossby wave and the quasi-stationary wave.

Hirooka, T.↗