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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Exploiting the IR: Solar and stellar spectroscopy in the IR

Recent instrumental advances have provided the capability to perform high resolution spectroscopy, in the thermal infrared region of the solar spectrum, with high sensitivity. The 8 to 12 micron region was extensively observed using Fourier transform (FTS) and laser heterodyne techniques. The continuous opacity of the solar atmosphere, due to H(-), increases with wavelength in the infrared region longward of 1.6 microns. Consequently thermal infrared observations probe the upper photosphere, and give an insight into the dynamics and structure of this region. The most notable spectral features in the 10 micron window include pure rotation lines of OH, and emission lines due to high-n states in MgI and AlI. The high-n lines due to MgI and AlI are important to solar and stellar physics because of their very large Zeeman sensitivity. The recent development of a cryogenic grating postdispenser for the FTS has allowed low-noise solar observations of these lines in 90 seconds. Limited mapping of the lines in a sunspot penumbra was performed, and gives information of the structure of the penumbral magnetic field. Although the MgI lines were detected in red giant spectra, instrumental sensitivity is not yet sufficient to see them in stars where significant magnetic fields are expected.

Deming, Drake↗
NASA NTRS1988

The Design and Use of a Temperature-Compensated Hot-Film Anemometer System for Boundary-Layer Flow Transition Detection on Supersonic Aircraft

An airborne temperature-compensated hot-film anemometer system has been designed, fabricated, and used to obtain in-flight airfoil boundary-layer flow transition data by the NASA Ames-Dryden Flight Research Facility. Salient features of the anemometer include near constant sensitivity over the full flight envelope, installation without coaxial wiring, low-noise outputs, and self-contained signal conditioning with dynamic and steady-state outputs. The small size, low-power dissipation, and modular design make the anemometer suitable for use in modern high-performance research aircraft. Design of the temperature-compensated hot-film anemometer and its use for flow transition detection on a laminar flow flight research project are described. Also presented are data gathered in flight which is representative of the temperature-compensated hot-film anemometer operation at subsonic, transonic, and supersonic flight conditions.

Chiles, Harry R.↗
NASA NTRS1988

Improved methods for the measurement and analysis of stellar magnetic fields

The paper presents several improved methods for the measurement of magnetic fields on cool stars which take into account simple radiative transfer effects and the exact Zeeman patterns. Using these methods, high-resolution, low-noise data can be fitted with theoretical line profiles to determine the mean magnetic field strength in stellar active regions and a model-dependent fraction of the stellar surface (filling factor) covered by these regions. Random errors in the derived field strength and filling factor are parameterized in terms of signal-to-noise ratio, wavelength, spectral resolution, stellar rotation rate, and the magnetic parameters themselves. Weak line blends, if left uncorrected, can have significant systematic effects on the derived magnetic parameters, and thus several methods are developed to compensate partially for them. The magnetic parameters determined by previous methods likely have systematic errors because of such line blends and because of line saturation effects. Other sources of systematic error are explored in detail. These sources of error currently make it difficult to determine the magnetic parameters of individual stars to better than about + or - 20 percent.

Saar, Steven H.↗
NASA NTRS1988

A 20 GHz low noise, low cost receiver for digital satellite communication system, ground terminal applications

A 45 month effort for the development of a 20 GHz, low-noise, low-cost receiver for digital, satellite communication system, ground terminal applications is discussed. Six proof-of-concept receivers were built in two lots of three each. Performance was generally consistent between the two lots. Except for overall noise figure, parameters were within or very close to specification. While noise figure was specified as 3.5 dB, typical performance was measured at 3.0 to 5.5 dB, over the full temperature range of minus 30 C to plus 75 C.

Allen, Glen↗
NASA NTRS1988

A high voltage power converter for space astronomy applications

A dc-dc low-power, high-voltage converter for use in space is described which furnishes a commandable, low-noise dc output in the range of 0 to -7500 V. The converter is suitable for biasing of detectors commonly employed in space astronomy, microchannel plates, photomultipliers, and gas discharge detectors. The converter's reliability has been demonstrated by accelerated life testing under thermal vacuum. The electrical and mechanical design, packaging, layout and fabrication techniques, and tests employed are described.

Ray, David C.↗
NASA NTRS1988

Gaussian approximation versus nearly exact performance analysis of optical communication systems with PPM signaling and APD receivers

A 25-Mb/s direct-detection optical communication system that used Q = 4 PPM (pulse-position modulation) signaling was constructed and its performance measured under laboratory conditions. The system used a single-mode AlGaAs laser diode (lambda = 834 nm) and low-noise silicon avalanche photodiode (APD). A procedure for numerically computing system performance is given that uses the nearly exact Webb approximation of the true Conradi distribution for the APD output and does not require excessive amounts of computer time. Comparison revealed that modeling the APD ouptut as a Gaussian process under conditions of negligible background radiation and low (less than 10 to the -12 A) APD bulk leakage currents leads to substantial underestimates of optimal APD gain and overestimates of system bit error probability. Examples illustrate the breakdown of the Gaussian approximation in assessing system performance. The measured performance was in excellent agreement with that predicted by the computational procedure. The system achieved a bit error probability of 10 to the -6 at a received signal energy, corresponding to an average of 60 absorbed photons/bit and optimal APD gain of 700.

Davidson, Frederic M.↗
NASA NTRS1989

A search for a dynamical attractor in Cygnus X-1

A method used for searching for low-dimensional attractors in fluctuating signals is applied to the aperiodicity observed in Cyg X-1. The analysis technique for determining the dimension of an attractor given its light curve, and the practical limitations in applying the technique, are described. The requirement of large amounts of low-noise data is found to be very important in using the technique. No low-dimensional attractor is found for the set of Cyg X-1 data used, but evidence of an attractor with large dimension may be present.

Lochner, James C.↗
NASA NTRS1989

A closed-cycle refrigerator for cooling maser amplifiers below 4 Kelvin

A helium refrigerator utilizing the Gifford-McMahon/Joule-Thomson (GM/JT) cycle was designed and tested to demonstrate the feasibility of using small closed-cycle refrigerators as an alternative to batch-filled cryostats for operating temperatures below 4 K. The systems could be used to cool low-noise microwave maser amplifiers located in large parabolic antennas. These antennas tilt vertically, making conventional liquid-filled dewars difficult to use. The system could also be used for a non-tilting beam waveguide antenna to reduce the helium consumption of a liquid helium cryostat. The prototype system is adjustable to provide 700 mW of cooling at 2.5 K to 3 W at 4.3 K. Performance of the unit is not significantly affected by physical orientation. The volume occupied by the refrigerator is less than 0.1 cu m. Two JT expansion stages are used to maximize cooling capacity per unit mass flow. The heat exchangers were designed to produce minimum pressure drop in the return gas stream. Pressure drop for the entire JT return circuit is less than 5 kpa at a mass flow of 0.06 g/sec when operating at 2.5 K.

Britcliffe, M.↗
NASA NTRS1989

Wideband phase-locked angular modulator

A phase-locked loop (PLL) angular modulator scheme has been proposed which has the characteristics of wideband modulation frequency response. The modulator design is independent of the PLL closed-loop transfer function H(s), thereby allowing independent optimization of the loop's parameters as well as the modulator's parameters. A phase modulator implementing the proposed scheme was built to phase modulate a low-noise phase-locked signal source at the output frequency of 2290 MHz. The measurement results validated the analysis by demonstrating that the resulting baseband modulation bandwidth exceeded that of the phase-locked loop by over an order of magnitude. However, it is expected to be able to achieve much wider response still.

Nguyen, L.↗
NASA NTRS1989

The 32-GHz performance of the DSS-14 70-meter antenna: 1989 configuration

The results of preliminary 32 GHz calibrations of the 70 meter antenna at Goldstone are presented. Measurements were done between March and July 1989 using Virgo A and Venus as the primary efficiency calibrators. The flux densites of theses radio sources at 32 GHz are not known with high accuracy, but were extrapolated from calibrated data at lower frequencies. The measured value of efficiency (0.35) agreed closely with the predicted value (0.32), and the results are very repeatable. Flux densities of secondary sources used in the observations were subsequently derived. These measurements were performed using a beamswitching radiometer that employed an uncooled high-electron mobility transistor (HEMT) low-noise amplifier. This system was installed primarily to determine the performance of the antenna in its 1989 configuration, but the experience will also aid in successful future calibration of the Deep Space Network (DSN) at this frequency.

Gatti, M. S.↗
NASA NTRS1989

Telecommunications technology development for the Deep Space Network

The telecommunications technology that is currently being developed for the Deep Space Network (DSN), a system providing communications and navigation support for NASA's deep space missions, is discussed. The major areas of development include Ka-band (32 GHz) technology, beam waveguide antennas, low-noise amplifiers, coding, navigation techniques, high-power transmitters, and optical technology. The expected payoffs of the new technology during the mid-1990's and later are examined.

Yuen, J. H.↗
NASA NTRS1989

User RF requirements for a Ka-band data relay satellite link

The user G/T and EIRP requirements were determined for a data relay satellite link consisting of a forward link to 360 Mbps at 23 GHz and a return link to 2 Gbps at 26.5 GHz. Hardware for this data link would be a modular expansion to the NASA Data Link Module. Calculations were based on a data relay satellite model of predetermined characteristics patterned after the NASA Tracking and Data Relay Satellite (TDRS). The desired data rates could be achieved with a G/T of 21.7 dB/deg K (forward link) and an EIRP of 68.2 dBW (return link) for the user satellite. Hardware configurations meeting these requirements are discussed in terms of RF performance, efficiency, reliability, and modular flexibility. A planar array configuration emerges as the logical candidate for most NASA missions. Pertinent Ka-band technology and certain ongoing research efforts are reviewed. Areas of particular interest include new power device families, 0.25-micron low-noise HEMT technology, and fiber optic distribution and control of RF arrays.

Copeland, David J.↗
NASA NTRS1961

Project Echo: Receiving System

A tracking horn-reflector antenna, a maser preamplifier (and standby parametric preamplifier), and a special FM demodulator were combined to form a low-noise receiving system which made possible the establishment of a high-quality voice circuit via the Echo I passive satellite. This paper describes the 2390-Mc receiving system located at the Bell Telephone Laboratories facility in Holmdel, New Jersey.

Ohm, E. A.↗
NASA NTRS1961

Project Echo: 961-Mc Lower - Sideband Up - Converter for Satellite-Tracking Radar

A 961-Mc lower-sideband up-converter was specially designed to serve as preamplifier for the satellite-tracking radar used in Project Echo. The amplifier and its power supply are separately boxed and are installed directly behind the tracking antenna. The amplifier has been functioning most satisfactorily and has been used in routine manner to track the Echo satellite from horizon to horizon. This paper describes the design considerations, and details the special steps taken to ensure that the amplifier met the particular system needs of low noise, absolute stability, insensitivity to temperature fluctuations, and high input-power level before the onset of gain compression. The satisfactory operation of this amplifier confirms the great potentiality of parametric amplifiers as stable, low-noise, high-frequency receivers.

Uenohara, M.↗
NASA NTRS1982

Pocket ECG electrode

A low-noise electrode suited for sensing electrocardiograms when chronically and subcutaneously implanted in a free-ranging subject. The electrode comprises a pocket-shaped electrically conductive member with a single entrance adapted to receive body fluids. The exterior of the member and the entrance region is coated with electrical insulation so that the only electrolyte/electrode interface is within the member remote from artifact-generating tissue. Cloth straps are bonded to the member to permit the electrode to be sutured to tissue and to provide electrical lead flexure relief.

Lund, Gordon F.↗
NASA NTRS2026

The Canadian Galactic Emission Mapper (CGEM) A Cosmic Microwave Foreground Experiment

The Canadian Galactic Emission Mapper (CGEM) is a 4-meter single-dish radio telescope located at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, Canada. CGEM is designed to map polarized Galactic synchrotron emission across the entire northern sky at 8-10 GHz with 1 MHz frequency resolution and ∼ 0.5 degree angular resolution. Its goal is to obtain high-fidelity, low-noise maps of polarized Galactic synchrotron radiation, at frequencies where synchrotron dominates, in order to provide a reliable template for CMB B−mode foreground cleaning. We will show on sky performance of CGEM’s single-pixel azimuthally-symmetric telescope, its coherent, dual-polarized radiometer, and show maps made from commissioning data from the first few months of operation.

Cosmic microwave background↗
DOE OSTI2025

Automating Sensor Characterization with Bayesian Optimization

The development of novel instrumentation requires an iterative cycle with three stages: design, prototyping, and testing. Recent advancements in simulation and nanofabrication techniques have significantly accelerated the design and prototyping phases. Nonetheless, detector characterization continues to be a major bottleneck in device development. During the testing phase, a significant time investment is required to characterize the device in different operating conditions and find optimal operating parameters. The total effort spent on characterization and parameter optimization can occupy a year or more of an expert's time. In this work, we present a novel technique for automated sensor calibration that aims to accelerate the testing stage of the development cycle. This technique leverages closed-loop Bayesian optimization (BO), using real-time measurements to guide parameter selection and identify optimal operating states. We demonstrate the method with a novel low-noise CCD, showing that the machine learning-driven tool can efficiently characterize and optimize operation of the sensor in a couple of days without supervision of a device expert.

Cuevas-Zepeda, Julian [Chicago U., KICP; Chicago U↗
DOE OSTI2026

SPT-3G D1: Compton-$y$ maps using data from the SPT-3G and Planck surveys

We present thermal Sunyaev-Zel'dovich (tSZ) Compton-$y$ parameter maps constructed from two years (2019-2020) of observations with the South Pole Telescope (SPT) third-generation camera, SPT-3G, combined with data from the Planck satellite. Using a linear combination (LC) pipeline, we obtain a suite of reconstructions that explore different trade-offs between statistical sensitivity and suppression of astrophysical contaminants, including minimum-variance, CMB-deprojected, and CIB-deprojected $y$-maps. We validate these maps through different statistical techniques such as auto- and cross-power spectra with large-scale structure tracers as well as stacking on cluster locations. These tests are used to understand the balance between noise and astrophysical foreground residuals (such as the CIB) in combination with the recovery of the tSZ signal for different maps. For example, results from stacking at the location of clusters confirm the robustness of the recovered tSZ signal over the $\sim 1500\: {\rm deg}^2$ SPT-3G survey field used in this analysis. The high-resolution and low-noise maps produced here provide an important cosmological tool for future studies, including measurements of the Compton-$y$ map power spectrum, cross-correlations with other tracers of the large-scale structure, detailed modeling of cluster pressure profiles, and study of the thermodynamic state of the baryons in the Universe.

Maniyar, A. S. [Harvard-Smithsonian Ctr. Astrophys↗