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Results for “ATMOSPHERIC DENSITY”

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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

The effect of random fluctuations in atmospheric density on significant space shuttle reentry parameters.

The effects of realistic atmospheric density variations on reentry vehicles are investigated with the aid of a random model of atmospheric density and a series of Monte Carlo reentry trajectories generated for a typical delta-wing orbiter design. The random behavior of five major performance indicators is studied, namely, maximum dynamic pressure, maximum g load, maximum stagnation heating rate, down-range distance, and cross-range distance.

Campbell, J. W.↗
NASA NTRS1994

Windblown sand on Venus: The effect of high atmospheric density

The high density of the venusian atmosphere significantly affects aeolian saltation transport and may also allow rapid alterations in the radar backscatter cross-section of the surface. Saltation flux experiments were conducted under terrestrial and simulated venusian conditions to assess the effect of atmospheric density on aeolian transport of sediment. Total lane flux, the vertical distribution of saltating particles, and the average horizontal component of particle speed were measured and used to estimate the volumetric concentration of particles above the surface. Results show that so many particles are set into motion when wind speeds exceed a critical value that mid-air collisions are a common result, a condition termed 'choked' saltation. When choking occurs, there is a reduction in the rate at which the total saltation flux increases with increasing wind speed at least in part due to a reduction in the mean horizontal speed of the particles. Choked saltation on Venus may result in a reduction of the local aeolian erosion rate, the obliteration of aeolian bedforms, and rapid alteration of surface radar backscatter characteristics.

Williams, Steven H.↗
NASA NTRS2010

Determining Atmospheric-Density Profile of Titan

A method was developed for measuring the atmospheric density of Titan, the largest moon of Saturn, to create an accurate density profile as a function of altitude. This will allow mission planners to select safe flyby altitudes, and for navigation engineers to accurately predict the delta-v associated with those flybys. The spacecraft angular rate vector profile as a function of time is collected via telemetry from the onboard attitude estimator once every 2 seconds. The telemetry for thruster times, as a function of time, for eight Reaction Control System (RCS) thrusters is gathered, once a second, from the Propulsion Manager algorithm of the Cassini onboard attitude-control flight software. Using these data, the ground software computes the angular momentum vector profile and the per-axis external torque as a function of time imparted from the spacecraft only due to the atmospheric drag. The software can then determine the Titan atmospheric density profile as a function of time and altitude with the known values of spacecraft center of mass, the Titan-relative range and velocity data, the projected area, and the aerocenter, along with the estimated drag coefficient in a free molecular flow field.

Sarani, Siamak↗
NASA NTRS2011

Taylor Series Trajectory Calculations Including Oblateness Effects and Variable Atmospheric Density

Taylor series integration is implemented in NASA Glenn's Spacecraft N-body Analysis Program, and compared head-to-head with the code's existing 8th- order Runge-Kutta Fehlberg time integration scheme. This paper focuses on trajectory problems that include oblateness and/or variable atmospheric density. Taylor series is shown to be significantly faster and more accurate for oblateness problems up through a 4x4 field, with speedups ranging from a factor of 2 to 13. For problems with variable atmospheric density, speedups average 24 for atmospheric density alone, and average 1.6 to 8.2 when density and oblateness are combined.

Scott, James R.↗
NASA NTRS1994

Evaluation of semiempirical atmospheric density models for orbit determination applications

This paper presents the results of an investigation of the orbit determination performance of the Jacchia-Roberts (JR), mass spectrometer incoherent scatter 1986 (MSIS-86), and drag temperature model (DTM) atmospheric density models. Evaluation of the models was performed to assess the modeling of the total atmospheric density. This study was made generic by using six spacecraft and selecting time periods of study representative of all portions of the 11-year cycle. Performance of the models was measured for multiple spacecraft, representing a selection of orbit geometries from near-equatorial to polar inclinations and altitudes from 400 kilometers to 900 kilometers. The orbit geometries represent typical low earth-orbiting spacecraft supported by the Goddard Space Flight Center (GSFC) Flight Dynamics Division (FDD). The best available modeling and orbit determination techniques using the Goddard Trajectory Determination System (GTDS) were employed to minimize the effects of modeling errors. The latest geopotential model available during the analysis, the Goddard earth model-T3 (GEM-T3), was employed to minimize geopotential model error effects on the drag estimation. Improved-accuracy techniques identified for TOPEX/Poseidon orbit determination analysis were used to improve the Tracking and Data Relay Satellite System (TDRSS)-based orbit determination used for most of the spacecraft chosen for this analysis. This paper shows that during periods of relatively quiet solar flux and geomagnetic activity near the solar minimum, the choice of atmospheric density model used for orbit determination is relatively inconsequential. During typical solar flux conditions near the solar maximum, the differences between the JR, DTM, and MSIS-86 models begin to become apparent. Time periods of extreme solar activity, those in which the daily and 81-day mean solar flux are high and change rapidly, result in significant differences between the models. During periods of high geomagnetic activity, the standard JR model was outperformed by DTM. Modification of the JR model to use a geomagnetic heating delay of 3 hours, as used in DTM, instead of the 6.7-hour delay produced results comparable to or better than the DTM performance, reducing definitive orbit solution ephermeris overlap differences by 30 to 50 percent. The reduction in the overlap differences would be useful for mitigating the impact of geomagnetic storms on orbit prediction.

Cox, C. M.↗
NASA NTRS2019

Isolated Rotor Forward Flight Testing at Martian Atmospheric Density Data Report

With the recent interest in Martian exploration using Unmanned Aerial Vehicles (UAVs), an experimental study was conducted to investigate rotor performance at Martian atmospheric conditions. Both simulation and testing of rotors is vital for evaluating rotor performance and behavior, especially for operations at Martian atmospheric densities and pressures. One critical test that has not been performed to date is helicopter forward flight testing at Martian atmospheric densities. To achieve this, a test was conducted in a tunnel facility that could be evacuated to the atmospheric pressure and density of Mars. A 40-inch-diameter rotor, roughly approximating the scale of the proposed Mars Helicopter (MH) design by the NASA Jet Propulsion Laboratory (JPL), was tested in forward flight at Mars’ atmospheric pressure at the NASA Ames Planetary Aeolian Laboratory (PAL). In this forward flight testing, the drive system of the Martian Surface Wind Tunnel (MARSWIT) was never turned on; all wind speeds read were generated either through the rotor spinning or from facility effects. The goal of this experiment was to collect rotor thrust, rotational speed, power, torque, and acoustics measurements. Subsequently, these results can be used for correlation with simulated cases using a mid-fidelity Computational Fluid Dynamics (CFD) simulation. As expected, rotor thrust and power are drastically reduced at air densities 100 times lower than at sea level on Earth. In addition, Reynolds number effects seem to play a vital role at reduced pressure that cannot be neglected in the simulation.

One Atmosphere↗
NASA NTRS2011

An Investigation of How a Meteor Light Curve is Modified by Meteor Shape and Atmospheric Density Perturbations

This is a preliminary investigation of how perturbations to meteoroid shape or atmospheric density affect a meteor light curve. A simple equation of motion and ablation are simultaneously solved numerically to give emitted light intensity as a function of height. It is found that changing the meteoroid shape, by changing the relationship between the cross-section area and the mass, changes the curvature and symmetry of the light curve, while making a periodic oscillation in atmospheric density gives a small periodic oscillation in the light curve.

Stokan, E.↗
NASA NTRS2020

Forward Flight Rotor Performance at Martian Atmospheric Densities and Sensitivity to Low Reynolds Numbers

Much effort has been made to enhance exploration on Mars. In addition to a rover and Mars-orbiting satellites, a Mars Helicopter Technology Demonstrator was proposed by the NASA Jet Propulsion Laboratory (JPL) to augment planetary research for the Mars 2020 Mission. Understanding rotor performance is vital for operations at Martian atmospheric conditions. The work presented is a study investigating rotor performance at Martian atmospheric conditions. Forward flight rotor tests were conducted in the Planetary Aeolian Laboratory (PAL) at NASA Ames Research Center, which has the capability to evacuate the air in the chamber to reach Martian atmospheric densities. A 1-meter-diameter rotor, roughly approximating the Mars Helicopter Technology Demonstrator, was tested at multiple atmospheric densities, including that of Mars. Rotor rotational speed, thrust, torque, power, and airspeed measurements were collected during the test. These results were then correlated with simulated cases using a mid-fidelity computational fluid dynamics software, Rotorcraft CFD (RotCFD). C81Generator (C81Gen) was used to generate airfoil aerodynamic coefficient for the spanwise locations along the rotor. To observe the differences between the C81Gen flow type modes at low Reynolds number, the simulations at Martian atmospheric densities were run under the “fully turbulent”, and the fully laminar flow type. In addition, Reynolds number effects (within 2x104 to 9x104) on experimental thrust coefficient, power coefficient, and figure of merit were analyzed. Within this chord- based Reynolds number range, CT and FM decreased around 26% and 36%, respectively, while CP remained fairly constant, exhibiting variations of no more than 5.5%. Despite the challenges involved in testing at a large difference of atmospheric ensities between Earth and Mars, repeatable data was obtained in all the measurements at Martian atmospheric conditions.

Perez Perez, Brenda NAtalia↗
NASA NTRS1990

A comparison of operationally determined atmospheric densities from satellite orbit solutions and the exospheric temperature from the Jacchia-Roberts model

Operational orbit determination by the Flight Dynamics Division at the Goddard Space Flight Center has yielded a data base of orbit solutions covering the onset of solar cycle 22. Solutions for nine satellites include an estimated drag adjustment parameter (rho sub 1) determined by the Goddard Trajectory Determination System (GTDS). The rho sub 1 is used to evaluate correlations between density variations and changes in the following: 10.7-centimeter wavelength solar flux (F sub 10.7), the geomagnetic index A sub p, and two exospheric temperatures (T sub c and T sub infinity) adapted from the Jacchia-Roberts atmospheric density model in GTDS. T sub c depends on the daily and 81-day centered mean F sub 10.7; T sub infinity depends on T sub c and the geomagnetic index K sub p values. The highest correlations are between density and T sub infinity. Correlations with T sub c and F sub 10.7 are lower by 9 and 10 percent, respectively. For most cases, correlations with A sub p are considerably lower; however, significant correlations with A sub p were found for some high-inclination, moderate-altitude orbits. Results from this analysis enhance the understanding of the drag model and the accommodation of atmospheric density variations in the operational orbit determination support. The degree of correlation demonstrates the sensitivity of the orbit determination process to drag variations and to the input parameters that characterize aspects of the atmospheric density model. To this extent, the degree of correlation provides a measure of performance for methods of selecting or modeling the thermospheric densities using the solar F sub 10.7 and geomagnetic data as input to the process.

Ward, D. T.↗
NASA NTRS1985

Determination of atmospheric density using a space-launched projectile

A method is proposed that provides advance information about unpredictable atmospheric density dispersions that must be accommodated during random operations of aeroassisted-orbital-transfer vehicles (AOTVs). The principal feature is that a test or 'scout' projectile precedes the AOTV through the same region of the atmosphere as that of the predicted transatmospheric flight trajectory. The atmospheric density structure is determined from the vehicle's aerodynamic deceleration characteristics by on-board or ground-based tracking equipment. The time lag between passage of the projectile and the AOTV can be adjusted to only that time necessary to implement required guidance, navigation, and control (GN&C) corrections. The various strategies available to control the projectile's flight characteristics are analyzed in detail. The results are correlated with aerothermodynamic heating and materials requirements to ensure the survival of the projectile and, consequently, the capability of the AOTV to navigate a variable upper atmosphere within specified limits.

Menees, G. P.↗
NASA NTRS1979

Comparison of atmospheric density data from mass spectrometers and atmospheric drag on the Aeros satellites

The comparison of perigee density data near 230 km for satellite Aeros-A has been extended to the complete mission time. The average ratio between orbital drag derived density and mass spectrometer measurements is very near to 1 with a large scatter reflected by a standard deviation of the order of 20%. A method of comparison was developed and tested which uses the observed rate of change of orbital period in comparison with the orbital decay computed from the actual mass spectrometer data measured at discrete positions along the orbit. This method proves that deviations from the average ratio of 1 between perigee densities from drag and mass spectrometers are due to the smoothing and poor resolution of the orbital drag technique.

Roemer, M.↗
NASA NTRS1979

Predictability of upper-atmospheric density and composition

Empirical models of upper-atmospheric density and composition are employed in a number of areas, ranging from basic research in atmospheric and ionospheric physics to practical applications in satellite ephemeris prediction. Such models are based on various kinds of data sets and have varying levels of complexity, strengths, and weaknesses. The characteristics of several of the widely used models are described and studies in which the predictions of these models were compared with observational data are reviewed. The relative advantages and limitations of the models in current use are discussed as well as ways in which the models might be improved.

Straus, J. M.↗