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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 253 records · Page 14
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NASA NTRS2024

Simulated Feasibility of 3D Lightning Mapping from Space

In addition to the awe it inspires, lightning can illuminate the microphysical processes hidden away within deep convection. The current generation of space-based lightning mapping uses mostly 2D optical imaging to connect overall flash characteristics to their parent storm dynamics, but are missing a dimension’s worth of information. With lightning now classified as an essential climate variable, future spaceborne mappers will need improved capabilities to take advantage of the 3D structure of lightning flashes to support meteorological and climate modeling. We report here on a study of the feasibility of implementing a radio frequency (RF)–based network of satellites for 3D lightning mapping in high resolution from low Earth orbit (LEO). Lightning sources are simulated using existing tools of the Lightning Mapping Array (LMA), modified for orbital detection, and spatially reconstructed using a Levenberg-Marquardt geolocation algorithm to assess sources of uncertainty in these solutions. We analyze the benefits and limitations of this approach compared to existing orbital and ground-based methods. Results of this study show that lightning can be mapped in 3D with a vertical location accuracy better than 2 km using as few as five satellites in LEO capable of measuring the time-of-arrival of impulsive RF signals in the very high frequency (VHF) band. The consequence of this study is that high-resolution, spaceborne 3D mapping of lightning is achievable across most of the globe, having crucial implications for our understanding of not only lightning, but also severe weather development, climate science, and more.

CubeSpark↗
NASA NTRS2020

Shape Validation and RF Performance of Inflatable Antennas

Inflatable aperture antennas are an emerging technology that is being investigated for potential use in science and exploration missions. In particular, for missions to Mars and beyond, large deployable aperture antennas can provide the antenna gain required for high data rate communications, where the necessary antenna diameter exceeds the available volume of typical launch vehicle platforms. As inflatable aperture antennas have not been proven fully qualified for space missions, the author's Master's Thesis assessed the Ruze equation in characterizing this antenna technology. Inflatable aperture antennas do not follow a parabolic shape, and so the Ruze equation is not applicable due to the macroscopic shape errors of this technology. Therefore, geometric evaluations of the surface profile cannot simply correlate antenna gain degradation with the root-mean-square shape error with a parabolic surface. Consequently, the focus of this work was to derive an accurate mathematical model of an inflatable aperture antenna in order to characterize its Radio Frequency (RF) performance. Calculus of Variations methodologies were used to derive the surface profile shape of the inflatable aperture antenna. Physical Optics techniques were used to generate the antenna pattern profile. Validation testing of the predicted inflatable antenna shape model was performed through use of Laser Radar metrology measurements on an inflatable test article. Assessments of the RF performance of the inflatable aperture antenna, compared with nominally shaped paraboloidal antennas, were obtained through simulations of both technologies using a common diameter, depth, and arc length. Assessments of the RF performance of the inflatable aperture antenna was also performed against itself for changes in distance of the antenna feed location in the axial direction. Whereas the Ruze equation is limited to assessing gain reduction, this effort will also assess beam spreading and first side lobe angle and magnitude. The ability to characterize the RF response of this antenna will provide for an improved understanding of this technology. The accurate representation of the shape of this type of antenna technology will help to identify the most appropriate ways in which this technology could be utilized in planning future communication architectures for NASA missions to Mars and beyond.

Welch, Bryan W.↗
NASA NTRS2020

Shape Validation and RF Performance of Inflatable Antennas

Inflatable aperture antennas are an emerging technology that is being investigated for potential use in science and exploration missions. In particular, for missions to Mars and beyond, large deployable aperture antennas can provide the antenna gain required for high data rate communications, where the necessary antenna diameter exceeds the available volume of typical launch vehicle platforms. As inflatable aperture antennas have not been proven fully qualified for space missions, the author's Master's Thesis assessed the Ruze equation in characterizing this antenna technology. Inflatable aperture antennas do not follow a parabolic shape, and so the Ruze equation is not applicable due to the macroscopic shape errors of this technology. Therefore, geometric evaluations of the surface profile cannot simply correlate antenna gain degradation with the root-mean square shape error with a parabolic surface. Consequently, the focus of this work was to derive an accurate mathematical model of an inflatable aperture antenna to in order to characterize its Radio Frequency (RF) performance. Calculus of Variations methodologies were used to derive the surface profile shape of the inflatable aperture antenna. Physical Optics techniques were used to generate the antenna pattern profile. Validation testing of the predicted inflatable antenna shape model was performed through use of Laser Radar metrology measurements on an inflatable test article. Assessments of the RF performance of the inflatable aperture antenna, compared with nominally shaped paraboloidal antennas, were obtained through simulations of both technologies using a common diameter, depth, and arc length. Assessments of the RF performance of the inflatable aperture antenna was also performed against itself for changes in distance of the antenna feed location in the axial direction. Whereas the Ruze equation is limited to assessing gain reduction, this effort will also assess beam spreading and first side lobe angle and magnitude. The ability to characterize the RF response of this antenna will provide for an improved understanding of this technology. The accurate representation of the shape of this type of antenna technology will help to identify the most appropriate ways in which this technology could be utilized in planning future communication architectures for NASA missions to Mars and beyond.

Welch, Bryan↗
NASA NTRS1998

Ion Energy Distributions and their Relative Abundance in Inductively Coupled Plasmas

Study of kinetics of ions and neutrals produced in high density inductively coupled plasma (ICP) discharges is of great importance for achieving a high degree of plasma assisted deposition and etching. In this paper, we present the ion energy distributions (IEDs) of various ions arriving at the grounded lower electrode. The ions were energy as well as mass analyzed by a combination of electrostatic analyzer-quadrupole mass spectrometer for pure Ar and CF4/Ar mixtures. The measurements have been made at gas pressures ranging from 30 to 100 mTorr. In addition, the IEDs were measured when the wafer-supporting electrode was also rf-powered and the effect of the self-bias was observed in the energy distributions of ions. The shapes of the IEDs are discussed an related to the sheath properties and measured electrical waveforms, as a function of pressure and applied power. Relative ion intensities were obtained by integration of each ion kinetic energy distribution function over its energy range.

Kim, J. S.↗
NASA NTRS1994

Design and implementation of a beam-waveguide mirror control system for vernier pointing of the DSS-13 antenna

The design and implementation of an antenna beam-waveguide (BWG) mirror position control system at the DSS-13 34-m antenna is presented. While it has several potential applications, a positioner on the last flat-plate BWG mirror (M6) at DSS 13 is installed to demonstrate the conical scan (conscan) angle-tracking technique at the Ka-band (32-GHz) operating frequency. Radio frequency (RF) beam-scanning predictions for the M6 mirror, computed from a diffraction analysis, are presented. From these predictions, position control system requirements are then derived. The final mechanical positioner and servo system designs, as implemented at DSS 13, are illustrated with detailed design descriptions given in the appendices. Preliminary measurements of antenna Ka-band beam scan versus M6 mirror tilt made at DSS 13 in December 1993 are presented. After reduction, the initial measurements are shown to be in agreement with the RF predicts. Plans for preliminary conscan experimentation at DSS 13 are summarized.

Alvarez, L. S.↗
NASA NTRS1994

Cryogenic probe station for use in automated microwave and noise figure measurements

A cryogenic measurement system capable of performing on-wafer RF testing of semiconductor devices and circuits has been developed. This 'CryoProbe Station' can wafer-probe devices and circuits at cryogenic temperatures, thus eliminating the need for wire bonds. The system operates under vacuum created by a sorption pump. It uses an open cycle cooling system that can be cooled with either liquid nitrogen or liquid helium. Presently, it can reach temperatures, as low as 80 K and 37 K for each of the coolants, respectively. The temperature can be raised using a heater and it is stabilized to within 0.2 K by use of a temperature controller. The CryoProbe Station features a 1 by 2 inch stage that can hold large circuits and calibration standards simultaneously. The system is used with a Hewlett Packard 8510C Automatic Network Analyzer (ANA) to obtain S-parameter data over the frequency range 0.045-26.5 GHz. S-parameter data on HEMT (high electron mobility transistors) devices has been obtained with this station. With the use of DEEMBED software from NIST, detailed transmission line studies have been performed. Although the CryoProbe Station is designed for frequencies up to 26.5 GHz, useful transmission line data has been obtained for frequencies as high as 40 GHz. The CryoProbe station has also been used with the ATN noise figure measurement system to perform automatic, temperature dependent noise figure measurements.

Taub, Susan R.↗
NASA NTRS1973

Study of blood flow sensing with microwave radiometry

A study and experimental investigation has been performed to determine the feasibility of measuring regional blood flow and volume in man by means of microwave radiometry. An indication was expected of regional blood flow from measurement of surface and subsurface temperatures with a sensitive radiometer. Following theoretical modeling of biological tissue, to determine the optimum operating frequency for adequate sensing depth, a sensitive microwave radiometer was designed for operation at 793 MHz. A temperature sensitivity of of 0.06 K rms was realized in this equipment. Measurements performed on phantom tissue models, consisting of beef fat and lean beefsteak showed that the radiometer was capable of sensing temperatures from a depth between 3.8 and 5.1 cm. Radiometric and thermodynamic temperature measurements were also performed on the hind thighs of large dogs. These showed that the radiometer could sense subsurface temperatures from a depth of, at least, 1.3 cm. Delays caused by externally-generated RF interference, coupled with the lack of reliable blood flow measurement equipment, prevented correlation of radiometer readings with reginal blood flow. For the same reasons, it was not possible to extend the radiometric observations to human subjects.

Porter, R. A.↗
NASA NTRS1995

DSS-24 microwave holography measurements

The JPL DSN Microwave Antenna Holography System (MAHST) was applied to the newly constructed DSS-24 34-m beam-waveguide antenna at Goldstone, California. The application of MAHST measurements and corrections at DSS 24 provided the critical RF performance necessary to not only meet the project requirements and goals, but to surpass them. A performance increase of 0.35 dB at X-band (8.45 GHz) and 4.9 dB at Ka-band (32 GHz) was provided by MAHST, resulting in peak efficiencies of 75.25 percent at X-band and 60.6 percent at Ka-band (measured from the Cassegrain focus at f1). The MAHST enabled setting the main reflector panels of DSS 24 to 0.25-mm rms, making DSS 24 the highest precision antenna in the NASA/JPL DSN. The precision of the DSS-24 antenna (diameter/rms) is 1.36 x 10(exp 5), and its gain limit is at 95 GHz.

Rochblatt, D. J.↗
NASA NTRS2012

Calibration Procedure for Measuring S-Parameters in Balun Applications on 150-ohm High-Speed Cables

In the radiofrequency (RF) world, in order to characterize cables that do not conform to the typical 50-omega impedance, a time domain reflectometer (TDR) would probably be the simplest and quickest tool to attain this goal. In the real world, not every engineer has a TDR at their disposal; however, they most likely have a network analyzer available. Given a generic 50-omega vector network analyzer (VNA), we would like to make S-parameter measurements for non-50-omega devices (DUTs). For that, we utilize RF balanced/unbalanced transformers (called baluns for short), which are primarily used to match the impedance between the two VNA ports and the DUT's input and output ports, for the two-port S-parameter measurements.

Theofylaktos, Onoufrios↗
NASA NTRS1964

Electronic systems.

Spacecraft RF electronic systems covering voice communications, telemetry, trajectory measurements and digital command system

SPACECRAFT ELECTRONIC EQUIPMENT↗
NASA NTRS1987

In situ process diagnostics of silane plasma for device-quality a-Si:H deposition

Coherent anti-Stokes Raman spectroscopy (CARS) and mass spectrometry (MS) have been applied to in situ process diagnostics of a silane plasma for device-quality a-Si:H film deposition. Silane depletion was directly measured by CARS and is linearly dependent on RF power in the region of 4-12 W with a slope of 0.5 percent/mW-sq cm. The depletion is also dependent on SiH4 flow rate starting with a 50 percent depletion at a low flow rate of 5.6 sccm and asymptotically approaching an 8 percent depletion at a flow rate of 80 sccm. The mass spectral line signal intensity of disilane increases with RF power and shows an apparent transition at 6 W. Disilane formation in silane plasma, film deposition rate, and silane depletion ratio as a function of the RF power indicate that the film growth mechanism in the low-power region of 3.5-6.5 W is substantially different from that in the high-power region of 6.5-12 W.

Shing, Y. H.↗
NASA NTRSDate not supplied

Modeling Methods for 3D Lightning Mapping from Space

Global lightning detection has advanced greatly over the past few decades both on ground and from orbit. Ground-based systems like the Lightning Mapping Array (LMA) excel at high-precision 3D reconstruction of local flashes, while spaceborne lightning sensors have much larger potential coverage but have been limited by coarser resolution and often rely on data from other instruments to determine flash location. The primary focus of this study is to examine the level of flash detail that can be expected from one or more low-Earth orbiting small satellites that combine VHF and optical measurements of lightning, which is a new mission concept called CubeSpark. The goal of CubeSpark is to map the 3D charge structure of thunderstorms at 1-2 km spatial resolution on a global scale, enabling a host of new atmospheric and space electricity studies. In order to maximize the potential data quality and minimize potential cost, flashes were simulated beneath single- and multi-satellite configurations. In the multi-satellite approach, RF detectors on each of the six satellites would measure the arrival times of impulsive VHF sources to collectively pinpoint their locations in 3D and reconstruct flashes with higher resolution than has been achieved from space. A single-station approach for 3D observation of lightning would follow the method of determining altitudes of strong VHF sources that produce trans-ionospheric pulse pairs (TIPPs) while relying on an on-board high-resolution optical day/night lightning mapper for approximate horizontal flash locations. Here we present preliminary results comparing the expected data fidelity and accuracy between these methods to inform potential satellite missions like CubeSpark.

lightning↗
NASA NTRS1975

Short range miniaturized biotelemetry system

A biotelemetry system for measuring and transmitting EKG, EMG, and EEG data by an RF link to a receiver was designed, developed, and delivered. The system is battery operated with the batteries and transmitting electronics an integral part of the electrode sensors. The low frequency response of 0.05 Hz assures faithful reproduction of detailed EKG and all measurements are made by the utilization of two electrode sensors.

Lorenz, R.↗
NASA NTRS1981

Techniques for prediction of large nonanalytic reflector antenna performance

Projected spacecraft missions for communications, radio astronomy and earth observations indicate a need for very large (on the order of 100 meters) space deployable or erectable antennas. This paper discusses a numerical method of analyzing reflector characteristics which is applicable to large reflector antennas whose surfaces are subject to mechanical and thermal distortions as well as fabrication and deployment errors. A technique of describing nonanalytic surface configurations by a finite number of known (measured) points was successfully applied in a computer model to predict the RF radiation pattern of a reflector using aperture plane integration techniques. The accuracy of the results is shown to be both a function of the number of measured points used and of their distribution.

Moskowitz, S. M.↗
NASA NTRS1990

Summary of interference measurements at selected radio observatories

Results are presented from a series of RF interference (RFI) observations conducted during 1989 and 1990 at selected radio astronomy observatories in order to choose a site for the SETI, where the local and orbital RFI would be as benign as possible for observations of weak electromagnetic signals. These observatories included the DSS13 at Goldstone (California), the Arecibo Observatory (Puerto Rico), the Algonquin Radio Observatory in Ottawa (Canada), the Ohio State University Radio Observatory in Columbus (Ohio), and the NRAO in Green Bank (West Virginia). The observations characterize the RFI environment at these sites from 1 to 10 GHz, using radio astronomy antennas, feeds, and receivers; SETI signal processors; and stand-alone equipment built specifically for this purpose. The results served as part of the basis for the selection (by the NASA SETI Microwave Observing Project) of NRAO as the site of choice for SETI observations.

Tarter, Jill C.↗
NASA NTRS2003

Precise Heater Controller with rf-Biased Josephson Junctions

Paramagnetic susceptibility thermometers used in fundamental physics experiments are capable of measuring temperature changes with a precision of a part in 2 x 10(exp 10). However, heater controllers are only able to control open-loop power dissipation to about a part in 10(exp 5). We used an array of rf-biased Josephson junctions to precisely control the electrical power dissipation in a heater resistor mounted on a thermally isolated cryogenic platform. Theoretically, this method is capable of controlling the electrical power dissipation to better than a part in 10(exp 12). However, this level has not yet been demonstrated experimentally. The experiment consists of a liquid helium cell that also functions as a high-resolution PdMn thermometer, with a heater resistor mounted on it. The cell is thermally connected to a temperature-controlled cooling stage via a weak thermal link. The heater resistor is electrically connected to the array of Josephson junctions using superconducting wire. An rf-biased array of capacitively shunted Josephson junctions drives the voltage across the heater. The quantized voltage across the resistor is Vn = nf(h/2e), where h is Planck's constant, f is the array biasing frequency, e is the charge of an electron, and n is the integer quantum state of the Josephson array. This results in an electrical power dissipation on the cell of Pn = (Vn)(sup 2/R), where R is the heater resistance. The change of the quantum state of the array changes the power dissipated in the heater, which in turn, results in the change of the cell temperature. This temperature change is compared to the expected values based on the known thermal standoff resistance of the cell from the cooling stage. We will present our initial experimental results and discuss future improvements. This work has been funded by the Fundamental Physics Discipline of the Microgravity Science Office of NASA, and supported by a no-cost equipment loan from Sandia National Laboratories.

Green, Colin J.↗