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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Skylab is falling - Strategies for reentry

Planning for the Skylab reentry, options for influencing the reentry, and a discussion of the Penn State drag modulation scheme are presented. The history of and risks in connection with Skylab reentry, and the NASA and the Penn State schemes for extending Skylab life are discussed. Coordinate systems and equations of motions describing the Skylab attitude motion, aerodynamic damping, and six-degree-of-freedom simulation are considered to derive structural damping models for Skylab, and to determine if stabilization is possible, and if it is, if the TACS (attitude-control) system can retumble the vehicle. It is concluded that at least 12 hours are required to carry out the Penn State drag modulation, and natural stabilization after a period of tumbling is possible but cannot be confirmed due to limitations in the modeling of aerodynamic properties, internal damping, and atmospheric density.

Kaplan, M. H.↗
NASA NTRS1979

MSFC solar activity predictions for satellite orbital lifetime estimation

The procedure to predict solar activity indexes for use in upper atmosphere density models is given together with an example of the performance. The prediction procedure employs a least square linear regression model to generate the predicted smoothed vinculum R sub 13 and geomagnetic vinculum A sub p(13) values. Linear regression equations are then employed to compute corresponding vinculum F sub 10.7(13) solar flux values from the predicted vinculum R sub 13 values. The output is issued principally for satellite orbital lifetime estimations.

Fuler, H. C.↗
NASA NTRS1979

Solar-induced variations of environment affecting manned space flight and spacecraft operations

Estimates of short and long term solar activity are required for calculating variations in the environment with regard to spacecraft charging, radiation effects, and orbital lifetime. Correlations appear to exist between the time of solar activity and the time of operational anomalies due to electrical discharges when the dielectric surfaces of geosynchronous spacecraft are charged by interaction with the ambient plasma to levels above breakdown voltage. An ability to predict the solar induced variation variability of the plasmas could permit refinement of design criteria. The influence of the radiation on spacecraft materials, systems, and manned operations is summarized. Solar radition effects on the orbital altitude atmospheric density environment and spacecraft lifetimes are also considered.

Johnson, W. G.↗
NASA NTRS1980

Shuttle program. Solar activity prediction of sunspot numbers, predicted solar radio flux

A solar activity prediction technique for monthly mean sunspot numbers over a period of approximately ten years from February 1979 to January 1989 is presented. This includes the predicted maximum epoch of solar cycle 21, approximately January 1980, and the predicted minimum epoch of solar cycle 22, approximately March 1987. Additionally, the solar radio flux 10.7 centimeter smooth values are included for the same time frame using a smooth 13 month empirical relationship. The incentive for predicting solar activity values is the requirement of solar flux data as input to upper atmosphere density models utilized in mission planning satellite orbital lifetime studies.

Johnson, G. G.↗
NASA NTRS1980

Studies of auroral X-ray imaging from high altitude spacecraft

Results of a study of techniques for imaging the aurora from a high altitude satellite at X-ray wavelengths are summarized. The X-ray observations allow the straightforward derivation of the primary auroral X-ray spectrum and can be made at all local times, day and night. Five candidate imaging systems are identified: X-ray telescope, multiple pinhole camera, coded aperture, rastered collimator, and imaging collimator. Examples of each are specified, subject to common weight and size limits which allow them to be intercompared. The imaging ability of each system is tested using a wide variety of sample spectra which are based on previous satellite observations. The study shows that the pinhole camera and coded aperture are both good auroral imaging systems. The two collimated detectors are significantly less sensitive. The X-ray telescope provides better image quality than the other systems in almost all cases, but a limitation to energies below about 4 keV prevents this system from providing the spectra data essential to deriving electron spectra, energy input to the atmosphere, and atmospheric densities and conductivities. The orbit selection requires a tradeoff between spatial resolution and duty cycle.

Mckenzie, D. L.↗
NASA NTRS1981

SUMS preliminary design and data analysis development

The preliminary analysis and data analysis system development for the shuttle upper atmosphere mass spectrometer (SUMS) experiment are discussed. The SUMS experiment is designed to provide free stream atmospheric density, pressure, temperature, and mean molecular weight for the high altitude, high Mach number region.

Hinson, E. W.↗
NASA NTRS1980

On the importance of reverse current ohmic losses in electron-heated solar flare atmospheres

The passage of a beam of nonthermal electrons through the flaring solar atmosphere is considered, paying particular attention to the requirement that the beam be stable to the generation of plasma turbulence. The ratio is computed of energy losses due to reverse current ohmic heating, and heating by Coulomb collisions, respectively, for the greatest flux which can pass stably through the atmosphere. It is demonstrated that this ratio is determined by the low energy cutoff of the beam, by the electron temperature of the ambient atmosphere, and by the electron to ion temperature ratio. It is also independent of the atmospheric density.

Emslie, A. G.↗
NASA NTRS1980

A low-order global gravity field of Venus and dynamical implications

An estimate of sixth-degree and sixth-order harmonic coefficients of the global gravity field of Venus is obtained by processing the long periodic variations of the mean orbital elements of the Pioneer Venus orbiter. Approximately 220 days of data are included in this reduction, which provides almost complete longitudinal coverage. Oblateness is estimated to be -5.97 + or - 3.2 x 10 to the -6. It is noted that the amplitudes of other coefficients are similar to the predicted coefficients using Kaula's rule under equal stress assumption. Atmospheric density values as a function of altitude are obtained to help model drag perturbation. A radial acceleration map at 100 km above the Venus surface is generated, and correlation between gravity anomalies and major topographic features is observed. Spectral analysis of the harmonic model suggests that the interior density anomalies are like those on earth. The orientation angles of the principal axes of the moments of inertia are computed, and deviation of the maximum moment of inertia axis from the spin axis is observed to be small (less than 5 deg). It is found that the minimum moment of inertia axis passes through the Aphrodite and Beta regions.

Ananda, M. P.↗
NASA NTRS1981

Integrated propulsion for near-Earth space missions. Volume 2: Technical

The calculation approach is described for parametric analysis of candidate electric propulsion systems employed in LEO to GEO missions. Occultation relations, atmospheric density effects, and natural radiation effects are presented. A solar cell cover glass tradeoff is performed to determine optimum glass thickness. Solar array and spacecraft pointing strategies are described for low altitude flight and for optimum array illumination during ascent. Mass ratio tradeoffs versus transfer time provide direction for thruster technology improvements. Integrated electric propulsion analysis is performed for orbit boosting, inclination change, attitude control, stationkeeping, repositioning, and disposal functions as well as power sharing with payload on orbit. Comparison with chemical auxiliary propulsion is made to quantify the advantages of integrated propulsion in terms of weight savings and concomittant launch cost savings.

Dailey, C. L.↗
NASA NTRS1982

The structure, energy balance, and winds of cool stars

The phenomena associated with magnetic fields in the Sun are summarized and it is shown that similar phenomena occur in cool stars. High dispersion spectra are providing unique information concerning densities, atmospheric extension, and emission line widths. A recent unanticipated discovery is that the transition lines are redshifted (an antiwind) in beta Dra (G2 Ib) and perhaps other stars. This is interpreted as indicating downflows in closed magnetic flux tubes as are seen in the solar flux tubes above sunspots. The G and K giants and supergiants are classified as active stars, quiet stars, or hybrid stars depending on whether their atmospheres are dominated by closed magnetic flux tubes, open field geometries, or a predominately open geometry with a few closed flux tubes embedded.

Linsky, J. L.↗
NASA NTRS1982

The composition and vertical structure of the lower cloud deck on Venus

Excluding the insertion of a probe into the lower Venus atmosphere, the only means of examining the atmospheric properties below the upper cloud layer are by passive or active radio techniques. Particularly, in a radio occultation experiment, the amplitude and Doppler data of a signal which has been refracted by the dense Venus atmosphere provide temperature, pressure, atmospheric density, cloud mass content, and some information about the cloud composition. The Venus orbiting spacecraft Pioneer Venus has provided radio occultation data for more than two years. The present investigation has the primary goal to use the absorption coefficient profiles derived from the radio occultation experiment to determine the mass content and composition of the Venusian lower deck. Attention is given to an experiment description, liquid content calculations, the mass content equation, the subtraction of gaseous absorbers, dielectric constant measurements, the concentration profile, the spherical shell model, and mass content profiles for all orbits.

Cimino, J.↗
NASA NTRS1983

On the flight derived/aerodynamic data base performance comparisons for the NASA Space Shuttle entries during the hypersonic regime

Aerodynamic performance data from the first four Shuttle reentry flights are compared with preflight predictions covering hypersonic longitudinal mode down to Mach 2. The extraction of the flight coefficients, as measured by the spacecraft angular rates and the linear accelerations, derived from the inertial measurement unit, the best estimate trajectory, and the remotely measured atmosphere are discussed. The ground predictions were developed from 30,000 hr of wind tunnel testing. Actual flight data are presented for 80-260 kft, from Mach 2-26, comprising the dynamic pressure, the vehicle air relative attitude angles, control surface deflections, reaction jet activity, and body axis rates and accelerations. The second and fourth flights gave results which deviated from predictions between 230-260 kft. The accuracy limits of the derived atmospheric densities are considered, together with potential data base updates in the light of limitations imposed on the corrections by available flight data.

Findlay, J. T.↗
NASA NTRS1983

Development of environmental criteria guidelines for aerospace vehicle design

The types of guideline data on natural environmental conditions for the various major geographic locations that are applicable to the design of aerospace vehicles and associated equipment are discussed. Since relationships between aerospace vehicle parameters and atmospheric variables cannot always be clearly defined, there should be a close working relationship and team philosophy between the design/operational engineer and the respective organizations' aerospace meteorologists. Consideration should be given to protecting aerospace vehicles from some extremes by using support equipment and specialized monitoring personnel to advise on the expected occurrence of critical environmental conditions. It is pointed out that the services of these specialized personnel may be very economical in comparison with the more expensive designing that would be necessary to cope with all environmental possibilities. The environment considered here includes wind, atmospheric electricity, upper atmospheric density, and solar wind.

Turner, R. E.↗
NASA NTRS1983

Minimum-fuel aeroassisted coplanar orbit transfer using lift-modulation

Minimum-fuel trajectories and lift controls are computed for aeroassisted coplanar transfer from high orbit to low orbit. The optimal aeroassisted transfer requires less fuel than the all-propulsive Hohmann transfer for a wide range of high orbit to low orbit transfers. The optimal control program for the atmospheric portion of the transfer is to fly at maximum positive L/D initially to recover from the downward plunge, and then, to fly at negative L/D to level off the flight, such that the vehicle skips out of the atmosphere with a flight path angle near zero degrees. To avoid excessive heating rates, the vehicle flies initially at high angle of attack in order to slow down higher in the atmosphere, allowing recovery from the downward plunge, which occurs subsequently using the maximum positive L/D, to take place at a lower atmospheric density, or equivalently, at a higher altitude.

Mease, K. D.↗
NASA NTRS1984

Dynamic model of the Earth's upper atmosphere

An initial modification to the MSF/J70 Thermospheric Model, in which the variations due to sudden geomagnetic disturbances upon the Earth's upper atmospheric density structure were modeled is presented. This dynamic model of the geomagnetic variation included is an improved version of one which SAO developed from the analysis of the ESRO 4 mass spectrometer data that was incorporated in the Jacchia 1977 model. The variation with geomagnetic local time as well as with geomagnetic latitude are included, and also the effects due to disturbance of the temperature profiles in the region of energy deposition.

Slowey, J. W.↗
NASA NTRS1984

Meteorological accuracy requirements for aerobraking orbital transfer vehicles

Accuracy requirements for the prediction of atmospheric density for a transfer mission from geosynchronous orbit to low earth orbit using an aerobraking orbital transfer vehicle are presented. Uniform density variations such as would occur seasonally and diurnally were considered as well as density 'pockets' similar to what may have been observed on some of the Space Shuttle Orbiter entry flights. Variations in the lift-to-drag ratio from 0.3 to 1.5 were evaluated, with the values of the ratio of the vehicle weight to the product of the aerodynamic lift coefficient and the aerodynamic reference area ranging from 20 to 100 lb/sq ft. The results of the study indicated no problems for the range of lift-to-drag ratio values considered for uniform density variations of at least + or - 50 percent. However, density 'pockets' created problems if variations of + or - 30 percent from nominal occurred over altitude ranges of 1,000 to 10,000 ft.

Skalecki, L. M.↗
NASA NTRS1983

Venus gravity field - Pioneer Venus Orbiter navigation results

The gravity field of Venus has been modeled by a spherical harmonic expansion of the potential to degree and order seven. The estimates of these coeficients were obtained by combining information from 43 short arcs (4 hr) of line-of-sight Doppler data centered at periapsis. The data arcs were distributed in longitude and time over more than two circulations of Venus by the Pioneer Venus Orbiter subperiapsis point which was confined to the band of latitudes from 14 deg N to 17 deg N. Convergence of the solution has been assured by iterating upon the initial estimate. All estimates were performed with zero a priori information on the gravity coefficients. Since the altitude of periapsis for most of the orbits was within the sensible Venusian atmosphere, drag effects on the estimated harmonics have been removed using an exponential atmosphere density model. Estimates of the mass parameter (GM) of Venus using this dataset are also evaluated.

Williams, B. G.↗