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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 487 records · Page 27

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NASA NTRS1976

The statistical significance of error probability as determined from decoding simulations for long codes

The very low error probability obtained with long error-correcting codes results in a very small number of observed errors in simulation studies of practical size and renders the usual confidence interval techniques inapplicable to the observed error probability. A natural extension of the notion of a 'confidence interval' is made and applied to such determinations of error probability by simulation. An example is included to show the surprisingly great significance of as few as two decoding errors in a very large number of decoding trials.

Massey, J. L.↗

NASA NTRS1977

Spacecraft flight control with the new phase space control law and optimal linear jet select

An autopilot designed for rotation and translation control of a rigid spacecraft is described. The autopilot uses reaction control jets as control effectors and incorporates a six-dimensional phase space control law as well as a linear programming algorithm for jet selection. The interaction of the control law and jet selection was investigated and a recommended configuration proposed. By means of a simulation procedure the new autopilot was compared with an existing system and was found to be superior in terms of core memory, central processing unit time, firings, and propellant consumption. But it is thought that the cycle time required to perform the jet selection computations might render the new autopilot unsuitable for existing flight computer applications, without modifications. The new autopilot is capable of maintaining attitude control in the presence of a large number of jet failures.

Bergmann, E. V.↗

NASA NTRS1977

Vortex lattice prediction of subsonic aerodynamics of hypersonic vehicle concepts

The vortex lattice method introduced by Lamar and Gloss (1975) was applied to the prediction of subsonic aerodynamic characteristics of hypersonic body-wing configurations. The reliability of the method was assessed through comparison of the calculated and observed aerodynamic performances of two National Hypersonic Flight Research Facility craft at Mach 0.2. The investigation indicated that a vortex lattice model involving 120 or more panel elements can give good results for the lift and induced drag coefficients of the craft, as well as for the pitching moment at angles of attack below 10 to 15 deg. Automated processes for calculating the local slopes of mean-camber surfaces may also render the method suitable for use in preliminary design phases.

Pittman, J. L.↗

NASA NTRS1977

The Photicon

The Photicon is a novel imaging optical detector utilizing a conventional semitransparent photocathode, imaging electrostatic optics, microchannel plates, and a crossed-wire-grid position-sensitive charge detector. Its sensitivity to single optical photons over a two-dimensional area, high-resolution imaging, and timing capability render it useful for recording scintillations from X-ray image converters in X-ray astronomy. A digital word indicating the position of a single photon event is produced; the image can be stored in an array or serially. Spatial resolution to 20 microns in a 25 mm diam active area detector is reported, and modifications to achieve a spectral range of 120-730 nm are mentioned.

Kellogg, E.↗

NASA NTRS1977

A generalized vortex lattice method for subsonic and supersonic flow applications

If the discrete vortex lattice is considered as an approximation to the surface-distributed vorticity, then the concept of the generalized principal part of an integral yields a residual term to the vorticity-induced velocity field. The proper incorporation of this term to the velocity field generated by the discrete vortex lines renders the present vortex lattice method valid for supersonic flow. Special techniques for simulating nonzero thickness lifting surfaces and fusiform bodies with vortex lattice elements are included. Thickness effects of wing-like components are simulated by a double (biplanar) vortex lattice layer, and fusiform bodies are represented by a vortex grid arranged on a series of concentrical cylindrical surfaces. The analysis of sideslip effects by the subject method is described. Numerical considerations peculiar to the application of these techniques are also discussed. The method has been implemented in a digital computer code. A users manual is included along with a complete FORTRAN compilation, an executed case, and conversion programs for transforming input for the NASA wave drag program.

Miranda, L. R.↗

NASA NTRS1969

Transformer regulated self-stabilizing chopper

A self-stabilizing voltage regulator is described. Direct current voltage regulation employing a series transistor rendered conductive during various portions of a cycle is controlled by saturation of an autotransformer. The constant volt-second capacity of the transformer provides conduction time inverse to the input voltage whereby average output voltage is maintained constant. Conduction commenced in response to short gate signals, and resistor feedback for degenerative turn-off of the transistor was after transformer saturation. Standard output filters are also included.

Raposa, F. L.↗

NASA NTRS1978

Optical conversion method

An optical pickup comprising an electrooptical device located between two crossed polarizing devices all positioned along a common optical axis is described for switching a TV system between a color mode and a black and white mode. Embodiments in which the electrooptical system is used as a neutral density filter, a selective color filter, or a light shutter as applied to a television camera are described. Where the optical system is used as a selective color filter to produce light beams of alternating color in a field sequential color television system, deactivation of the optical system renders the television a black and white system.

Perry, W. E.↗

NASA NTRS1977

Nitramine smokeless propellant research

A transient ballistics and combustion model was derived to represent the closed vessel experiment that is widely used to characterize propellants. The model incorporates the nitramine combustion mechanisms. A computer program was developed to solve the time dependent equations, and was applied to explain aspects of closed vessel behavior. It is found that the rate of pressurization in the closed vessel is insufficient at pressures of interest to augment the burning rate by time dependent processes. Series of T-burner experiments were performed to compare the combustion instability characteristics of nitramine (HMX) containing propellants and ammonium perchlorate (AP) propellants. It is found that the inclusion of HMX consistently renders the propellant more stable.

Source record↗

NASA NTRS1978

Sound propagation in a duct of periodic wall structure

A boundary condition, which accounts for the coupling in the sections behind the duct boundary, is given for the sound-absorbing duct with a periodic structure of the wall lining and using regular partition walls. The soundfield in the duct is suitably described by the method of differences. For locally active walls this renders an explicit approximate solution for the propagation constant. Coupling may be accounted for by the method of differences in a clear manner. Numerical results agree with measurements and yield information which has technical applications.

Kurze, U.↗

NASA NTRS1978

Regulated high efficiency, lightweight capacitor-diode multiplier dc to dc converter

A voltage multiplier having a capacitor-diode voltage multiplying network is disclosed which is fed with voltage pulses from a dc source through a first switching means. Pulses of a second polarity are also supplied through a second switching means to the input of the capacitor-diode voltage multiplier from a second dc source whose voltage is adjustable to change the voltage of the pulses of second polarity. The switching means are alternately rendered conducting by signals from a control circuit. The second dc source may be controlled by a voltage comparator which compares the output voltage of the capacitor-diode voltage multiplier to the reference source.

Harrigill, W. T., Jr.↗

NASA NTRS1977

Some Martian Volcanic Features as Viewed from the Viking Orbiters

A summary is presented of the results of some new observations on Martian volcanic features made from the Viking orbiters. Most of these observations are concerned with the Tharsis and Alba regions. The youth, size, and style of the volcanic features in these areas render them particularly susceptible to analysis. Excellent coverage was also acquired of Apollinaris Patera. It has many features of the Tharsis shields, with a cliff around its circumference and a large central caldera. Olympus Mons and its vicinity are examined, taking into account the shield of Olympus Mons, mass movement features along the basal scarp, the basal plains, the relative ages of Olympus Mons and the basal plains, and grooved terrain.

Carr, M. H.↗

NASA NTRS1978

New concepts for Mercury orbiter missions

The next logical step in the exploration of Mercury is an orbiter mission. A conflict exists between those in the field of planetary sciences who desire a mission with a low circular orbit, and scientists in the fields and particles disciplines, who generally prefer a highly elliptical spacecraft orbit. The thermal environment imposed by the sun and planet render the low orbit intolerable for spacecraft using previous thermal control methods. A thermal control concept and a spacecraft mission concept have been developed which resolve these problems and promise a scientifically significant mission for the mid-1980s.

French, J. R.↗

NASA NTRS1978

Interpretation of observed cosmic microwave background radiation

The Alfven and Mendis (1977) conclusion that dust grains in galaxies render the universe opaque to cosmic microwave background at a red shift ratio equal to 40 is challenged by a calculation of the opacity of galactic dust grains to the microwave background radiation from the time of decoupling at emission red shift ratio equal to 1500 to the present in the standard big bang model. In the present calculation, evolutionary effects on grain opacity and abundance are estimated. At wavelengths used in studying the microwave background, the optical depth of the grains is found to be 0.18 when the deceleration parameter equals 0.03, and 0.05 when the deceleration parameter equals 0.5. The results indicate that microwave background can provide information on an early dense phase of the universe.

Pollaine, S.↗

NASA NTRS1977

The thermoremanence hypothesis and the origin of magnetization in iron meteorites

The intensity, relative stability and directional behavior in alternating field demagnetization of natural, saturation, thermal and spontaneous magnetization were studied for a variety of iron meteorites. Results show that remanence and relative stability increase from the coarser to the finer-grained samples. In addition, natural remanent magnetization coercivity spectra are found to soften with coarsening of the grain size. The link between fine structure and magnetization direction in octahedrites is also discussed. The combined effect of magnetocrystalline- and shape-anisotropy of the crystallographically ordered ferromagnetic kamacite alpha-phase renders the iron meteorites of little use for the study of ancient solar system fields.

Brecher, A.↗

NASA NTRS1977

The application of satellite data in monitoring strip mines

Strip mines in the New River Drainage Basin of Tennessee were studied through use of Landsat-1 imagery and aircraft photography. A multilevel analysis, involving conventional photo interpretation techniques, densitometric methods, multispectral analysis and statistical testing was applied to the data. The Landsat imagery proved adequate for monitoring large-scale change resulting from active mining and land-reclamation projects. However, the spatial resolution of the satellite imagery rendered it inadequate for assessment of many smaller strip mines, in the region which may be as small as a few hectares.

Sharber, L. A.↗

NASA NTRS1978

The zonally averaged circulation of the middle atmosphere

The steady-state, zonally averaged circulation of the middle atmosphere (15-125 km) is studied with a quasigeostrophic, numerical model that explicitly includes a self-consistent calculation of solar radiative heating due to O2 and O3 absorption, Newtonian cooling, Rayleigh friction, tropopause boundary conditions based on climatological averages, and the effects of vertically propagating planetary waves. It is found that the direct, radiatively driven pole-to-pole circulation at solstice is sufficient to account for the cold summer mesopause and warm isothermal winter mesosphere with associated zonal jets of realistic magnitude. The climatological heat and momentum fluxes associated with planetary wavenumber 2 have a negligible effect on the mean circulation. With planetary wavenumber 1, no steady-state solution could be obtained due to the formation of easterlies and hence critical layers in the winter mesosphere. The radiative heating associated with secondary peaks in the O3 density at the mesopause could render the polar mesopause region convectively unstable.

Schoeberl, M. R.↗

NASA NTRS1978

The beamed power microwave transmitting antenna

Beamed power refers to radiation techniques employing directional antennas for purposes of transferring energy in microwave form from one place to another. The peaceful uses of beamed power as applied to electric utilities functions and transportation concepts are considered. An investigation is conducted regarding the design approaches and techniques which can be used by the microwave component engineer to render beamed power systems potentially safe for humans and other biota. High-power microwave transmission antennas are proposed for beaming power from earth-orbiting satellites to receiving antennas (rectennas) on earth. Other applications include beaming power to run helicopters, aircraft, and aerostats equipped with rectennas. System designs must provide for techniques to yield microwave radiation levels that do not exceed allowable limits. Attention is given to beam surveillance techniques and the effects of an implementation of these techniques on the beamed power systems.

Dickinson, R. M.↗

NASA NTRS1978

Acoustic scattering from locally homogeneous turbulence

An equation is derived for acoustic scattering from the velocity and temperature fields of a drifting blob of air turbulence. The equation is solved for scattering from the mean and turbulent portions of both fields, and the time autocorrelation and power spectral density of the received signal are calculated. The mean velocity and temperature fields, as well as the corresponding turbulence intensity distributions, are allowed to be spatially nonuniform. The turbulent fields are required to be only locally homogeneous and locally stationary. It is shown that the common practice of representing antenna patterns by either truncating the flow or tapering the strength of the flow is, at least in the case of the transmitting pattern, not a bad approximation. Spectral broadening of the receiver signal due to convection of the small scattering eddies by macroeddies and by the mean flow in modeled, and the broadening by macroeddy convection is seen to render negligible the broadening which arises from the drift of the target flow through the antenna beam. The analysis reveals that only for target flows having a high degree of spatial uniformity and/or symmetry does the received positive-frequency power spectral density turn out to be symmetrical about a center frequency.

Ramsey, V. W.↗