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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 739 records · Page 41

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NASA NTRS1974

Energetic solar proton versus terrestrially trapped proton fluxes for the active years 1977 - 1983

Ratios of solar to trapped proton fluences were computed for circular-orbit, geocentric space missions to be flown during the active phase of the next solar cycle (1977-1983). The ratios are presented as functions of orbit altitude and inclination, mission duration, proton energy threshold, and the chance the mission planner is willing to take that the actually encountered solar proton fluence will exceed the design fluence provided by the statistical solar proton model. It is shown that the ratio is most sensitively dependent on orbit altitude and inclination, with trapped protons dominant for low inclination, low and mid altitude orbits and for high inclination, mid altitude orbits. Conversely, solar protons are dominant for high inclination, low altitude orbits, and for low and high inclination, high altitude orbits.

King, J. H.↗

NASA NTRS1974

A unified approach for the application of general perturbation theories to the artificial satellite problem

An Encke-type method is developed as well as a variation of parameters method, both of which use a non-Keplerian reference orbit. The regularized time is used in the numerical integration and the optimum value of n is found for each type of orbit investigated. Accuracy and computation time comparisons are made with a classical Cowell method. It should be noted that the element formulations developed and tested were found to be exceptionally numerically stable in the sense that it was possible to achieve numerical consistency order of very long integration periods - a property not available with the Cowell formulation - and therefore these formulations may be helpful for high precision calculations.

Alfriend, K. T.↗

NASA NTRS1975

Viking to Mars - The mission strategy

The Viking mission is discussed which will search for evidence of life on Mars by performing extended and closeup reconnaissance of the planet's surface. Previous unsuccessful Soviet attempts to land scientific payloads on Mars are summarized, and choices of landing sites for the two Viking landers are discussed. The onboard computers in both the orbiter and the two landers are described with emphasis on their 18,000-word memories and reprograming capabilities. The mission profiles and lander programs are outlined in detail, and lander experiments are discussed which will involve surface imaging, meteorological and seismometric measurements, soil sampling, lower atmosphere analysis, and searches for possible Martian microorganisms.

Sagan, C.↗

NASA NTRS1975

Averaged initial Cartesian coordinates for long lifetime satellite studies

A set of initial Cartesian coordinates, which are free of ambiguities and resonance singularities, is developed to study satellite mission requirements and dispersions over long lifetimes. The method outlined herein possesses two distinct advantages over most other averaging procedures. First, the averaging is carried out numerically using Gaussian quadratures, thus avoiding tedious expansions and the resulting resonances for critical inclinations, etc. Secondly, by using the initial rectangular Cartesian coordinates, conventional, existing acceleration perturbation routines can be absorbed into the program without further modifications, thus making the method easily adaptable to the addition of new perturbation effects. The averaged nonlinear differential equations are integrated by means of a Runge Kutta method. A typical step size of several orbits permits rapid integration of long lifetime orbits in a short computing time.

Pines, S.↗

NASA NTRS1977

Comet Halley - The orbital motion

The orbital motion of Comet Halley is investigated over the interval from A.D. 837 to 2061. Using the observations from 1607 through 1911, least-squares differential orbit corrections were successfully computed using the existing model for the nongravitational forces. The nongravitational-force model was found to be consistent with the outgassing-rocket effect of a water-ice cometary nucleus and, prior to the 1910 return, these forces are time-independent for nearly a millennium. For the 1986 return, viewing conditions are outlined for the comet and the related Orionid and Eta Aquarid meteor showers.

Yeomans, D. K.↗

NASA NTRS1978

Synthetic Aperture Radar Technology Conference, New Mexico State University, Las Cruces, N. Mex., March 8-10, 1978, Proceedings

The following aspects of SAR development are discussed: calibration techniques, image simulation and interpretability, antennas, data processing, and system design. Papers are presented on such topics as a postlaunch calibration experiment for the Seasat-A SAR, computer simulation of an orbital SAR system, definition study of the Shuttle Imaging Radar, custom LSI circuits for spaceborne SAR processors, and random sampling adaptively focusing SAR.

Source record↗

NASA NTRS1980

LeRC reduced gravity fluid management technology program

A survey of the reduced gravity fluid management technology program is presented. Information on reduced gravity fluid behavior, techniques for thermal control of cryogenic tankage, and design for fluid management systems are discussed. The development of Spacelab experiments, propellant management systems for orbit transfer vehicles, and computer techniques for simulating reduced gravity fluid dynamic processes is reported.

Aydelott, J. C.↗

NASA NTRS1980

A study of the lifetimes of geosynchronous transfer orbits

The study concerns the orbit lifetimes of spent upper stages that are used to boost NASA Space Transportation System payloads into geosynchronous transfer orbits. A semi-analytical method of trajectory computation was developed and applied to these particular orbits. It was found that gravitational perturbations of the sun, moon and oblate earth cause large changes in the perigee altitude. The following parameters have a strong influence on orbit lifetimes: Time of year of launch; Inertial orientation of orbital plane; Inclination of orbital plane.

Graf, O. F., Jr.↗

NASA NTRS1980

Performance analysis of the Spaceborne Laser Ranging System

The performance of the Spaceborne Laser Ranging System in the determination of distances between ground-based targets is discussed. The system consists of an orbiting pulsed laser distance measurement system that sequentially measures the distance to retroreflector arrays on the ground. Intersite distances are then determined from an analysis of the vertical distance data and the spacecraft orbital dynamics. Results of computer simulations indicate that for a six-day observing period with 50 percent cloud cover, uncertainties of 1 to 3 cm are expected for intertarget separations of 50 to 1200 km, with vertical uncertainties from 1 to 12 cm. Furthermore, it is found that by redetermining relative target positions, precision can be increased to less than 0.3 cm to 1 cm in the baseline and to 0.4 to 4 cm in vertical distance. It is concluded that with these precisions, strain and strain rate can be determined for crustal dynamics and earthquake studies, and geodetic surveys can be performed.

Kahn, W. D.↗

NASA NTRS1981

MAGSAT and aeromagnetic data in the North American continent

Problems were encountered in deriving a proper reference field to be subtracted from the aeromagnetic data obtained from Project MAGNET. Field models tried thus far do not seem to eliminate properly the main field. The MAGSAT data in the North American continent for the period November 1 to December 22, 1979 are being compiled and compared with MAGNET data. Efforts are being made to eliminate the orbital bias errors. A computer program was developed and successfully tested which computes a topographic profile of the Curie depth isotherm which fits best to the observed vector or scalar field magnetic data.

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NASA NTRS1981

MAGSAT data processing: A report for investigators

The in-flight attitude and vector magnetometer data bias recovery techniques and results are described. The attitude bias recoveries are based on comparisons with a magnetic field model and are thought to be accurate to 20 arcsec. The vector magnetometer bias recoveries are based on comparisons with the scalar magnetometer data and are thought to be accurate to 3 nT or better. The MAGSAT position accuracy goals of 60 m radially and 300 m horizontally were achieved for all but the last 3 weeks of Magsat lifetime. This claim is supported by ephemeris overlap statistics and by comparisons with ephemerides computed with an independent orbit program using data from an independent tracking network. MAGSAT time determination accuracy is estimated at 1 ms. Several errors in prelaunch assumptions regarding data time tags, which escaped detection in prelaunch data tests, and were discovered and corrected postlaunch are described. Data formats and products, especially the Investigator-B tapes, which contain auxiliary parameters in addition to the basic magnetometer and ephemeris data, are described.

Langel, R. A.↗

NASA NTRS1983

Booster and orbiter configurations

In the recent Future Space Transportation System (FSFS) study, a mission model was selected and a baseline vehicle which best met model requirements was shaped. This baseline was then analyzed for flight performance, structural and subsystem weight, and operation. Figures related to a payload of 150,000 lb in a 20-ft-diam by 90-ft-long envelope became the baseline. The existence of both space-based orbital transfer vehicles (OTVs) and a space station was assumed, taking into account a transfer of the payload from the launch vehicle to OTVs at the space station for final delivery to geosynchronous orbit (GEO). A computer-aided engineering system called Aerospace Vehicle Interactive Design (AVID) was employed in connection with baseline vehicle development. It was found that approximately three-fifth of the payload weight would be cryogenic propellants for OTVs. Attention is given to problems regarding the packaging of cryogenic tankage, a payload shroud, and studies of staging for two different booster propulsion units.

Wilhite, A. W.↗

NASA NTRS1984

Global mean sea surface based upon SEASAT altimeter data

A global mean sea surface based upon the SEASAT altimeter data was derived. A combination of crossing arc techniques, accurate SEASAT reference orbits, and a previously computed GOES-3/SEASAT mean sea surface were used in the computation process. This mean sea surface provides a basis for the determination of global ocean circulation patterns and for detailed analysis of the Earth's internal structure. A contour map of the global mean sea surface is presented.

Marsh, J. G.↗

NASA NTRS1984

Mission planning and operations of a Space Shuttle payload experiment: SIR-A

In November 1981 the first scientific payload was carried on board the second flight of the Space Shuttle. The principal instrument on that flight was a synthetic aperture radar. This paper is concerned with the operational concepts developed to achieve the objective of terrestrial geologic mapping by radar from earth orbit for this mission. Computer software was developed as an aid to mission design prior to the mission and as a replanning tool used during the mission: The first step in the development of software for future missions where such tools will become indispensable to meet the apparently contradictory objectives of complex observations and low cost.

Harris, H. M.↗

NASA NTRS1986

Interactive mission planning for a Space Shuttle flight experiment - A case history

Scientific experiments which use the Space Shuttle as a platform require the development of new operations techniques for the command and control of the instrument. Principal among these is the ability to simulate the complex maneuvers of the orbiter's path realistically. Computer generated graphics provide a window into the actual and predicted performance of the instrument and allow sophisticated control of the instrument under varying conditions. In October of 1984 the Shuttle carried a synthetic aperture radar built by JPL for the purpose of recording images of the earth surface. The mission deviated from planned operation in almost every conceivable way and provided an exacting test bed for concepts of interactive mission planning.

Harris, H. M.↗

NASA NTRS1986

Effect of subcooling on the on-orbit pressurization rate of cryogenic propellant tankage

The SOLA-ECLIPSE code is being developed to enable prediction of the behavior of cryogenic propellants in spacecraft tankage. A brief description of the formulations used for modeling heat transfer and for determining thermodynamic state is presented. Code performance is verified through comparison to experimental data for the self-pressurization of scale model liquid hydrogen tanks. SOLA-ECLIPSE is used to examine the effect of initial subcooling of the liquid phase on the self-pressurization rate of an on-orbit full scale liquid hydrogen tank typical for a chemical propulsion Orbital Transfer Vehicle. The computational predictions show that even small amounts of subcooling will significantly decrease the self-pressurization rate. Further, if the cooling is provided by a Thermodynamic Vent System, it is concluded that small levels of subcooling will maximize propellant conservation.

Hochstein, J. I.↗

NASA NTRS1990

Prediction of self-pressurization rate of cryogenic propellant tankage

The SOLA-ECLIPSE code is being developed to enable prediction of the behavior of cryogenic propellants in spacecraft tankage. A brief description of the formulations used for modeling heat transfer and for determining the thermodynamic state is presented. Code performance is verified through comparison to experimental data for the self-pressurization of scale-model liquid hydrogen tanks. SOLA-ECLIPSE is used to examine the effect of initial subcooling of the liquid phase on the self-pressurization rate of an on-orbit full-scale liquid hydrogen tank typical for a chemical-propulsion orbit transfer vehicle. The computational predictions show that even small amounts of subcooling will significantly decrease the self-pressurization rate. Further, if the cooling is provided by a thermodynamic vent system, it is concluded that small levels of subcooling will maximize propellant conservation.

Hochstein, John I.↗

NASA NTRS1990

Theoretical characterization of the 5Pi and 3Pi potential energy surfaces for NH + O yields N + OH

The reactant, product, and saddle point regions of the 5Pi and 3Pi potential energy surfaces for the reaction NH + O yields N + OH have been characterized using complete active space self consistent field/externally contracted configuration interaction calculations with large atomic natural orbital basis sets. The computed barrier heights are 5.6 and 11.7 kcal/mol on the 5Pi and 3Pi surfaces, respectively. Transition state theory with an Eckart tunneling correction is used to estimate the rate constant on the 5Pi surface.

Walch, Stephen P.↗