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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Reanalysis information for eigenvalues derived from a differential equation analysis formulation

The investigation reported demonstrates that in the case considered perturbation methods can be used in a straightforward manner to obtain reanalysis information. A perturbation formula for the buckling loads of a general shell of revolution is derived. The accuracy of the obtained relations and their range of application is studied with the aid of a specific example involving a particular stiffened shell of revolution.

Thornton, W. A.↗
NASA NTRS1980

Analysis of differential and active charging phenomena on ATS-5 and ATS-6

Spacecraft charging on the differential charging and artificial particle emission experiments on ATS 5 and ATS 6 were studied. Differential charging of spacecraft surfaces generated large electrostatic barriers to spacecraft generated electrons, from photoemission, secondary emission, and thermal emitters. The electron emitter could partially or totally discharge the satellite, but the mainframe recharged negatively in a few 10's of seconds. The time dependence of the charging behavior was explained by the relatively large capacitance for differential charging in comparison to the small spacecraft to space capacitance. A daylight charging event on ATS 6 was shown to have a charging behavior suggesting the dominance of differential charging on the absolute potential of the mainframe. Ion engine operations and plasma emission experiments on ATS 6 were shown to be an effective means of controlling the spacecraft potential in eclipse and sunlight. Elimination of barrier effects around the detectors and improving the quality of the particle data are discussed.

Olsen, R. C.↗
NASA NTRS1985

A new method of differential structural analysis of gamma-family basic parameters

The maximum likelihood method is used for the first time to restore parameters of electron photon cascades registered on X-ray films. The method permits one to carry out a structural analysis of the gamma quanta family darkening spots independent of the gamma quanta overlapping degree, and to obtain maximum admissible accuracies in estimating the energies of the gamma quanta composing a family. The parameter estimation accuracy weakly depends on the value of the parameters themselves and exceeds by an order of the values obtained by integral methods.

Melkumian, L. G.↗
NASA NTRS1984

Simulation and analysis of differential GPS

NASA is conducting a research program to evaluate differential Global Positioning System (GPS) concepts for civil helicopter navigation. It is pointed out that the civil helicopter community will probably be an early user of GPS because of the unique mission operations in areas where precise navigation aids are not available. However, many of these applications involve accuracy requirements which cannot be satisfied by conventional GPS. Such applications include remote area search and rescue, offshore oil platform approach, remote area precision landing, and other precise navigation operations. Differential GPS provides a promising approach for meeting very demanding accuracy requirements. The considered procedure eliminates some of the common bias errors experienced by conventional GPS. This is done by making use of a second GPS receiver. A simulation process is developed as a tool for analyzing various scenarios of GPS-referenced civil aircraft navigation.

Denaro, R. P.↗
NASA NTRS1991

Nucleation and crystallization of Na2O-2CaO-3SiO2 glass by differential thermal analysis

DTA is presently used to characterize the nucleation and crystallization processes of the Na2O-2CaO-3SiO2 glass. A nucleation rate-temperaturelike curve is obtained by plotting either the reciprocal of the temperature corresponding to the crystallization peak maximum, or the height of the crystallization peak, as a function of nucleation temperature. The nucleation-temperature range for this glass composition, 550-650 C, and the maximum nucleation temperature of 600 + or - 5 C, are found to be in excellent agreement with those associated with the classical nucleation technique, followed by isothermal crystallization. It is noted that when most of the nucleation occurs during the DTA measurements, a modified Kissinger equation must be used to calculate the crystallization energy.

Xu, Xiaojie J.↗
NASA NTRS1992

An analysis of differential impact melt-crater scaling and implications for the terrestrial impact record

The volume of impact melt relative to that of the transient cavity is known to increase with the magnitude of the impact event. This paper investigates the influence of that phenomenon on the nature of terrestrial impact craters. A model of impact melting was used to estimate the volume of melt produced during the impact of chondritic projectiles into granite targets at velocities of 15, 25, and 50 km per sec. The results were compared with observed melt volumes at terrestrial craters, which were collated from the literature and paired with the transient-cavity diameters of their respective craters. Results show that the record on terrestrial craters is not inconsistent with the predictions of the model.

Grieve, R. A. F.↗