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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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Recapitulation of results of lunar topography studies using radar techniques
A new hybrid method is presented for the analysis of the scattering and radiation by conformal antennas and arrays comprised of circular or rectangular elements. In addition, calculations for cavity-backed spiral antennas are given. The method employs a finite element formulation within the cavity and the boundary integral (exact boundary condition) for terminating the mesh. By virtue of the finite element discretization, the method has no restrictions on the geometry and composition of the cavity or its termination. Furthermore, because of the convolutional nature of the boundary integral and the inherent sparseness of the finite element matrix, the storage requirement is kept very low at O(n). These unique features of the method have already been exploited in other scattering applications and have permitted the analysis of large-size structures with remarkable efficiency. In this report, we describe the method's formulation and implementation for circular and rectangular patch antennas in different superstrate and substrate configurations which may also include the presence of lumped loads and resistive sheets/cards. Also, various modelling approaches are investigated and implemented for characterizing a variety of feed structures to permit the computation of the input impedance and radiation pattern. Many computational examples for rectangular and circular patch configurations are presented which demonstrate the method's versatility, modeling capability and accuracy.
Contents include the following: NASA's Missions and Aeronautics Research. Today's Air Traffic Control System. Development of Decision-Support Tools. The Center-TRACON Automation System (CTAS). The Traffic Management Advisor (TMA). The Multi-Center Traffic Management Advisor (McTMA). The Surface Management System (SMS). Future Directions: The Joint Planning and Development Office.
Finite element modeling has proven useful for accurtely simulating scattered or radiated fields from complex three-dimensional objects whose geometry varies on the scale of a fraction of a wavelength.
The design of a conformal antenna for use on UAV's (Unmanned Aerial Vehicle) and other aircraft can be enhanced with computational electromagnetic modeling to determine the expected radiation patterns of the antenna when mounted on the aircraft. However, detailed simulation of the antenna structure and the aircraft together requires significant computational resources and time which may not be available. This paper details several methods for estimating the radiation pattern of a 50 by 50-element patch antenna. The Conformal Lightweight Antenna Structures for Aeronautical Communication Technologies (CLASACT) Program aims to build and test a 14.25 gigaherz (Ku-band) conformal antenna on a NASA-owned UAV. The antenna is intended for satellite communications and will enable communication between a ground station and a UAV when the separation distance is too great for line-of-sight communication. It is estimated that a 2 degree beamwidth will be necessary, requiring a 50 by 50 array of patch elements. The narrow beamwidth requirement, together with an element spacing of 0.6 lambda means that the array length will be 30 wavelengths, electrically very large. Three methods of varying complexity are described for estimating the total far-field radiation pattern. The results are shown for each method in the form of a normalized power pattern.
A simple model of magnetic field perturbations driven by neutron star oscillations is used to estimate the electromagnetic power radiated by g-modes and torsional oscillations. The calculation assumes that the neutron star has a frozen-in magnetic field which is perturbed by the oscillatory motions of the surface. The disturbances propagate into the vacuum as outgoing electromagnetic waves. The relative effectiveness of Joule heating of the neutron star crust by pulsation-induced electric currents is estimated. It is concluded that electromagnetic damping is the dominant energy dissipation mechanism for quadrupole g-mode oscillations of neutron stars. For dipole spheroidal modes, both electromagnetic radiation and Joule heating are important, and there is no gravitational radiation emitted by these modes.
A new type of large area sensor for infrared imaging bolometers has been developed. It replaces the thin and fragile free-standing metal foils, which typically have been used, with a multi-layer coated sapphire (or diamond) substrate. Sapphire is transparent to mid-infrared wavelengths, is robust against transients, and can be thick enough to even be the vacuum window. The primary radiation absorber is still a thin deposited metal layer, but now it is partially insulated from the supporting sapphire substrate by a black (carbon-based) layer, which also acts as a blackbody remitter. Test results indicate 6× more noise equivalent power density (estimated NEPD = 23 W/m 2 at 5 ms camera exposure time, foil temperature decay time 60 ms) for a 2 μm gold-coated sapphire disk compared to estimated NEP = 4 W/m 2 at 1.8 ms exposure time, with foil decay time 420 ms, for a nominal 2.5 μm thick platinum-free-standing foil.
Characteristics of radiant flux in vicinity of earth, method for simulating distribution of flux, and effect of approximations on simulation fidelity
Preliminary data analysis for a physical fault injection experiment of a digital system exposed to High Intensity Radiated Fields (HIRF) in an electromagnetic reverberation chamber suggests a direct causal relation between the time profile of the field strength amplitude in the chamber and the severity of observed effects at the outputs of the radiated system. This report presents an analysis of the field strength modulation induced by the movement of the field stirrers in the reverberation chamber. The analysis is framed as a characterization of the discrete features of the field strength waveform responsible for the faults experienced by a radiated digital system. The results presented here will serve as a basis to refine the approach for a detailed analysis of HIRF-induced upsets observed during the radiation experiment. This work offers a novel perspective into the use of an electromagnetic reverberation chamber to generate upset-inducing stimuli for the study of fault effects in digital systems.
High energy particle and electromagnetic space radiation effects on thermal control coating, noting spectral absorptance for various conditions
Hydromagnetic radiation modulation and sampling telemetry - electromagnetic signal detection by magnetometer from spacecraft
Techniques for measurement of equilibrium and non equilibrium radiance of high temperature gases in electric driven shock tube
Dielectric loss tangent measurement in pyroelectric materials for EM radiation detectors and heat transfer sensors
As electric propulsion systems become ready to integrate with spacecraft systems, the impact of propulsion system radiated emissions are of significant interest. Radiated emissions from electromagnetic, electrostatic, and electrothermal systems have been characterized and results synopsized from the literature describing 21 space flight programs. Electromagnetic radiated emission results from ground tests and flight experiences are presented with particular attention paid to the performance of spacecraft subsystems and payloads during thruster operations. The impacts to transmission of radio frequency signals through plasma plumes are also reviewed.
As electric propulsion systems become ready to integrate with spacecraft systems, the impact of propulsion system radiated emissions are of significant interest. Radiated emissions from electromagnetic, electrostatic, and electrothermal systems have been characterized and results synopsized from the literature describing 21 space flight programs. Electromagnetic radiated emission results from ground tests and flight experiences are presented with particular attention paid to the performance of spacecraft subsystems and payloads during thruster operations. The impacts to transmission of radio frequency signals through plasma plumes are also reviewed.
Solutions are presented for the electromagnetic fields radiated by an arbitrarily oriented current filament located above a perfectly conducting ground plane and excited by a traveling current wave. Both an approximate solution, valid in the fraunhofer region of the filament and predicting the radiation terms in the fields, and an exact solution, which predicts both near and far field components of the electromagnetic fields, are presented. Both solutions apply to current waveforms which propagate along the channel but are valid regardless of the actual waveshape. The exact solution is valid only for waves which propagate at the speed of light, and the approximate solution is formulated for arbitrary velocity of propagation. The spectrum-magnitude of the fourier transform-of the radiated fields is computed by assuming a compound exponential model for the current waveform. The effects of channel orientation and length, as well as velocity of propagation of the current waveform and location of the observer, are discussed. It is shown that both velocity of propagation and an effective channel length are important in determining the shape of the spectrum.
A study into the problem of determining electromagnetic solutions at high frequencies for problems involving complex geometries, large sizes and multiple sources (e.g. antennas) has been initiated. Typical applications include the behavior of antennas (and radiators) installed on complex conducting structures (e.g. ships, aircrafts, etc..) with strong interactions between antennas, the radiation patterns, and electromagnetic signals is of great interest for electromagnetic compatibility control. This includes the overall performance evaluation and control of all on-board radiating systems, electromagnetic interference, and personnel radiation hazards. Electromagnetic computational capability exists at NASA LaRC, and many of the codes developed are based on the Moment Method (MM). However, the MM is computationally intensive, and this places a limit on the size of objects and structures that can be modeled. Here, two approaches are proposed: (i) a current-based hybrid scheme that combines the MM with Physical optics, and (ii) an Alternating Direction Implicit-Finite Difference Time Domain (ADI-FDTD) method. The essence of a hybrid technique is to split the overall scattering surface(s) into two regions: (a) a MM zone (MMZ) which can be used over any part of the given geometry, but is most essential over irregular and "non-smooth" geometries, and (b) a PO sub-region (POSR). Currents induced on the scattering and reflecting surfaces can then be computed in two ways depending on whether the region belonged to the MMZ or was part of the POSR. For the MMZ, the current calculations proceed in terms of basis functions with undetermined coefficients (as in the usual MM method), and the answer obtained by solving a system of linear equations. Over the POSR, conduction is obtained as a superposition of two contributions: (i) currents due to the incident magnetic field, and (ii) currents produced by the mutual induction from conduction within the MMZ. This effectively leads to a reduction in the size of linear equations from N to N - Npo with N being the total number of segments for the entire surface and Npo the number of segments over the POSR. The scheme would be appropriate for relatively large, flat surfaces, and at high frequencies. The ADI-FDTD scheme provides for both transient and steady state analyses. The restrictive Courant-Friedrich-Levy (CFL) condition on the time-step is removed, and so large time steps can be chosen even though the spatial grids are small. This report includes the problem definition, a detailed discussion of both the numerical techniques, and numerical implementations for simple surface geometries. Numerical solutions have been derived for a few simple situations.
Motion and radiation of charged particles in strong electromagnetic waves in plane and spherical waves