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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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NASA NTRS1973

Predawn enhancement of 6300-A emission observed near the plasmapause from the Isis-2 spacecraft.

Data from several Isis-2 spacecraft passes are described in which the 6300-A atomic oxygen red line photometer mapped intensity steps resembling the predawn enhancement. Comparison with the electron density measured at the spacecraft indicates a plasmapause influence on the 6300-A emission rate, in that the intensity varies roughly inversely with the electron density at 1400 km. A simple calculation demonstrates the idea that field line opacity differences for photoelectrons are significant across the plasmapause. The measured electron temperatures are inadequate to account for the 6300-A excitation, thus confirming that it must arise from another mechanism.

Shepherd, G. G.↗

NASA NTRS1977

Three-dimensional elastic stress and displacement analysis of finite geometry solids containing cracks

The line method of analysis is applied to the Navier-Cauchy equations of elastic equilibrium to calculate the displacement fields in finite geometry bars containing central, surface, and double-edge cracks under extensionally applied uniform loading. The application of this method to these equations leads to coupled sets of simultaneous ordinary differential equations whose solutions are obtained along sets of lines in a discretized region. Normal stresses and the stress intensity factor variation along the crack periphery are calculated using the obtained displacement field. The reported results demonstrate the usefulness of this method in calculating stress intensity factors for commonly encountered crack geometries in finite solids.

Kring, J.↗

NASA NTRS1977

Microstructure of a magnetotail fireball

We use high time resolution data from the magnetometer, LEPEDEA and plasma wave analyzer on IMP-7 to examine the microstructure of a long-duration magnetotail fireball event observed during an extended quiet period on November 9, 1972. We demonstrate that the magnetic field is turbulent with fluctuation time scales down to several seconds. These findings suggest that the magnetic merging process may be a highly turbulent one, possibly associated with a form of the tearing mode instability.

Coroniti, F. V.↗

NASA NTRS1977

Three-dimensional elastic stress and displacement analysis of finite geometry solids containing cracks

Kring, J.↗

NASA NTRS1977

Utilization of NASA Lewis mobile terminals for the Hermes satellite

The high power of the Hermes satellite enables two-way television and voice communication with small ground terminals. The Portable Earth Terminal (PET) and the Transportable Earth Terminal (TET) were developed and built by NASA-Lewis to provide communications capability to short-term users. The NASA-Lewis mobile terminals are described in terms of vehicles and onboard equipment, as well as operation aspects, including use in the field. The section on demonstrations divides the uses into categories of medicine, education, technology and government. Applications of special interest within each category are briefly described.

Edelman, E. A.↗

NASA NTRS1979

Photographic combustion characterization of LOX/hydrocarbon type propellants

Single element injectors and two fuels were tested with the aim of photographically characterizing observed combustion phenomena. The three injectors tested were the O-F-O triplet, the transverse like on like (TLOL), and the rectangular unlike doublet (RUD). The fuels tested were RP-1 and propane. The hot firings were conducted in a specifically constructed chamber fitted with quartz windows for photographically viewing the impingement spray field. All LOX/HC testing demonstrated coking with the RP-1 fuel leaving far more soot than the propane fuel. No fuel freezing or popping was experienced under the test conditions evaluated. Carbon particle emission and combustion light brilliance increased with Pc for both fuels although RP-1 was far more energetic in this respect. The RSS phenomena appear to be present in the high Pc tests as evidenced by striations in the spray pattern and by separate fuel rich and oxidizer rich areas. The RUD element was also tested as a fuel rich gas generator element by switching the propellant circuits. Excessive sooting occurred at this low mixture ratio (0.55), precluding photographic data.

Judd, D. C.↗

NASA NTRS1981

Some aspects of calculating flows about three-dimensional subsonic inlets

As a consequence of the growing interest in the development of V/STOL aircraft technology, efforts are being made to create new designs for a propulsion system which can be operated over a wide range of flight speeds, incidence angles, and throttle settings. In connection with these efforts, various inlet configurations have been proposed. The high experimental costs incurred in the study of various inlet geometries, led to the employment of a computational method for the investigation of inlets. Attention is given to the computer program, paneling and surface static pressure, surface flow pattern, and the inlet flow field. The reported investigation demonstrates that useful information for initial screenings may be obtained from potential flow calculations.

Kao, H. C.↗

NASA NTRS1982

Topological analysis of computed three-dimensional viscous flow fields

Computed solutions of the time-dependent, Reynolds-averaged Navier-Stokes equations for three dimensional flows having thin shear layers are analyzed using topological concepts. Specific examples include the transonic flow over a body of revolution with conical afterbody at moderate angles of incidence to the free stream. Experimental flow-visualization techniques are simulated graphically to visualize the computed flow. Scalar and vector fluid dynamics properties such as pressure, shear stress, and vorticity on the body surface are presented as topological maps, and their relationship to one another in terms of orientation and singular points is discussed. The extrapolation from these surface topologies toward the understanding of external flow-field behavior is and demonstrated.

Deiwert, G. S.↗

NASA NTRS1983

Calculation of viscous supersonic flows over finned bodies

The parabolized Navier-Stokes (PNS) equations are used to calculate the viscous, supersonic flow fields about a six-finned projectile and a generic four-finned missile at angles of attack. Since current computer speeds and storage preclude a fully three-dimensional calculation using the unsteady, Reynolds-averaged, Navier-Stokes equations, the applicability of the PNS equations to the above flow fields is of considerable interest. Two important aspects of the calculation are grid generation and the type of smoothing used to prevent nonphysical solutions. This paper includes a description of the grid-generation process. Results in the form of density contours and velocity vector plots are presented for the two configurations. The applicability of the PNS equations to the complicated flow fields considered is successfully demonstrated.

Rai, M. M.↗

NASA NTRS1984

Radiative and reconnection instabilities - Filaments and flares

The way in which the initial development of solar filament radiative cooling and the magnetic reconnection of a solar flare can occur in the center of a field-shear layer is demonstrated. Since the present treatment unites these two mechanisms, it indicates the common as well as the disparate features they possess. Unstable radiation serves to increase the Coulomb resistivity at the X-point, so that the reconnection is not self-quenching. The surprising dominance of the magnetic component of the perturbation in the midwavelength range indicates the need to examine the nonlinear saturation of the energy transport of the radiative mode, taking the accompanying magnetic reconnection and potential-energy release into account, for comparison with observations of filaments as well as for clues to the character of the preflare state.

Van Hoven, G.↗

NASA NTRS1984

Nonlinear evolution of the lower-hybrid drift instability

The results of simulations of the lower-hybrid drift instability in a neutral sheet configuration are described. The simulations use an implict formulation to relax the usual time step limitations and thus extend previous explicit calculations to weaker gradients, larger mass ratios, and long times compared with the linear growth time. The numerical results give the scaling of the saturation level, heating rates, resistivity, and cross-field diffusion and a demonstration by comparison with a fluid electron model that dissipation in the lower-hybrid drift instability is caused by electron kinetic effects.

Brackbill, J. U.↗

NASA NTRS1985

Extension of ground-based testing for large space structures

A major concern for future large space structures is the ability to verify their dynamic characteristics by ground test. This article presents the results of the multiple boundary conditions test (MBCT) approach, which provides a complete ground test of a large structure that will provide, in turn, the data necessary to construct a test-verified final mathematical model. Theoretical studies indicate that this approach can provide a better final model than a ground test of the full-scale very flexible structure in a 1-g field. The approach is demonstrated by a mathematical simulation.

Wada, B. K.↗

NASA NTRS1986

Path-constrained rendezvous - Necessary and sufficient conditions

The problem of path-constrained rendezvous in the vicinity of a Large Space Structure (LSS) was first introduced some years ago. The present contribution to this field centers on a demonstration that the problem can be reduced from a path-constraint problem to one of end-point constraints or certain (common) LSS geometries, under the assumption of an unrestrictive upper limit on the transfer time. This finding has been made under the assumption of a circular Keplerian orbit, and has been normalized with respect to orbital semimajor axis and LSS size. In addition to demonstrating this important simplification of the path-constrained rendezvous problem, the results of numerical simulations of path-constrained transfers from point-to-point on large spherical structures in orbit are discussed, and a series of conclusions having both architectural (design) and operational implications for LSS designers/operators is derived.

Soileau, K. M.↗

NASA NTRS1987

A zonal method for modeling 3-D aircraft flow fields with jet plume effects

A coupled zonal method has been developed for modeling flows about aircraft with highly integrated advanced nozzle installations in which the exhaust plume interacts with the aircraft flow field to enhance performance. A cost effective flow analysis is achieved by dividing the flow domain into zones and coupling the zonal solutions. PAN AIR is used to model the flow in the inviscid zone which surrounds the aircraft. The plume zone flow field is solved with a PNS code. The flow in the optional internal nozzle zone is modeled using a full Navier-Stokes code. An automated iterative procedure couples the inviscid and plume zones by passing updated boundary conditions between the zones. The coupled analysis provides converged solutions for the overall flow field. The method is demonstrated for a highly integrated nonaxisymmetric vectored nozzle installed on a swept-wing aircraft.

Roberts, D. W.↗

NASA NTRS1987

Multiple-angle observations of reflectance anisotropy from an airborne linear array sensor

An airborne pointable imaging multispectral linear array sensor has been developed for the multidirectional observation of surface reflectance anisotropy. The sensor design permits observations up to 45 deg off-nadir in three spectral bands (green, red, and near-infrared). Calibration permits the conversion of sensor data to radiance units with an absolute uncertainty of 6 percent. Observations of five field plots from seven view directions are discussed. Calibration and atmospheric corrections are used to derive hemispherical-directional reflectance factors. A three-term reflectance model is fit to the reflectance factors for each plot to represent the continuous distribution of reflectance factors with view direction. The reflectance model is integrated over all view directions to calculate bihemispherical reflectance factors. The calculated bihemispherical factors differed by 1 to 25 percent from values based on an assumption of isotropic reflectance depending on spectral band and field plot. These calculations demonstrate the technologic and scientific capabilities required for the remote characterization of surface reflectance anisotropy. Remote multidirectional observations are both feasible and needed to fully evaluate land reflectance characteristics.

Irons, James R.↗

NASA NTRS1987

Precision positioning of earth orbiting remote sensing systems

Decimeter tracking accuracy is sought for a number of precise earth sensing satellites to be flown in the 1990's. This accuracy can be achieved with techniques which use the Global Positioning System (GPS) in a differential mode. A precisely located global network of GPS ground receivers and a receiver aboard the user satellite are needed, and all techniques simultaneously estimate the user and GPS satellite states. Three basic navigation approaches include classical dynamic, wholly nondynamic, and reduced dynamic or hybrid formulations. The first two are simply special cases of the third, which promises to deliver subdecimeter accuracy for dynamically unpredictable vehicles down to the lowest orbit altitudes. The potential of these techniques for tracking and gravity field recovery will be demonstrated on NASA's Topex satellite beginning in 1991. Applications to the Shuttle, Space Station, and dedicated remote sensing platforms are being pursued.

Melbourne, William G.↗

NASA NTRS1989

Creation of current filaments in the solar corona

It has been suggested that the solar corona is heated by the dissipation of electric currents. The low value of the resistivity requires the magnetic field to have structure at very small length scales if this mechanism is to work. In this paper it is demonstrated that the coronal magnetic field acquires small-scale structure through the braiding produced by smooth, randomly phased, photospheric flows. The current density develops a filamentary structure and grows exponentially in time. Nonlinear processes in the ideal magnetohydrodynamic equations produce a cascade effect, in which the structure introduced by the flow at large length scales is transferred to smaller scales. If this process continues down to the resistive dissipation length scale, it would provide an effective mechanism for coronal heating.

Mikic, Z.↗

NASA NTRS1989

Characterization of fluid flow by digital correlation of scattered light

The objective is to produce a physical system suitable for a space environment that can measure fluid velocities in a three-dimensional volume by the development of a particle correlation velocimetry technique. Experimental studies were conducted on a field test cell to demonstrate the suitability and accuracy of digital correlation techniques for measuring two-dimensional fluid flows. This objective was satisfied by: (1) the design of an appropriate illumination and detection system for making velocity measurements within a test cell; (2) the design and construction of a test cell; (3) the preliminary evaluations on fluid and seeding requirements; and (4) the performance of controlled tests using a multiple exposure correlation technique. This presentation is represented by viewgraphs with very little text.

Gilbert, John A.↗