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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Infrared detector responsivity measured simultaneously at multiple frequencies

The responsivity (the ratio of the output electrical signal to the incident radiation power) of an IR detector is measured at several frequencies simultaneously. A computer-controlled variable frequency chopper is used. Chopper modulation of a blackbody is square-wave-like, hence measurements can be taken not only at the fundamental frequency but also at the harmonics. The technique gives excellent agreement with the classical technique of measuring the fundamental response alone at a set of modulation frequencies. With a small enough aperture and a high enough chopper speed, agreement can be within five percent out to 31 times the fundamental frequency. The technique allows the rapid and automated acquisition of the frequency response of IR detectors, which may then be screened for responsivity, noise, and noise equivalent power.

Brasunas, John C.↗
NASA NTRS1997

Detector power linearity requirements and verification techniques for TMI direct detection receivers

A system (36, 98) for determining the linearity of an RF detector (46, 106). A first technique involves combining two RF signals from two stable local oscillators (38, 40) to form a modulated RF signal having a beat frequency, and applying the modulated RF signal to a detector (46) being tested. The output of the detector (46) is applied to a low frequency spectrum analyzer (48) such that a relationship between the power levels of the first and second harmonics generated by the detector (46) of the beat frequency of the modulated RF signal are measured by the spectrum analyzer (48) to determine the linearity of the detector (46). In a second technique, an RF signal from a local oscillator (100) is applied to a detector (106) being tested through a first attenuator (102) and a second attenuator (104). The output voltage of the detector (106) is measured when the first attenuator (102) is set to a particular attenuation value and the second attenuator (104) is switched between first and second attenuation values. Further, the output voltage of the detector (106) is measured when the first attenuator (102) is set to another attenuation value, and the second attenuator (104) is again switched between the first and second attenuation values. A relationship between the voltage outputs determines the linearity of the detector (106).

Reinhardt, Victor S.↗
NASA NTRS2012

Connect Global Positioning System RF Module

The CoNNeCT Global Positioning System RF Module (GPSM) slice is part of the JPL CoNNeCT Software Defined Radio (SDR). CoNNeCT is the Communications, Navigation, and Net working reconfigurable Testbed project that is part of NASA's Space Communication and Nav igation (SCaN) Program. The CoNNeCT project is an experimental dem onstration that will lead to the advancement of SDRs and provide a path for new space communication and navigation systems for future NASA exploration missions. The JPL CoNNeCT SDR will be flying on the International Space Station (ISS) in 2012 in support of the SCaN CoNNeCT program. The GPSM is a radio-frequency sampler module (see Figure 1) that directly sub-harmonically samples the filtered GPS L-band signals at L1 (1575.42 MHz), L2 (1227.6 MHz), and L5 (1176.45 MHz). The JPL SDR receives GPS signals through a Dorne & Margolin antenna mounted onto a choke ring. The GPS signal is filtered against interference, amplified, split, and fed into three channels: L1, L2, and L5. In each of the L-band channels, there is a chain of bandpass filters and amplifiers, and the signal is fed through each of these channels to where the GPSM performs a one-bit analog-to-digital conversion (see Figure 2). The GPSM uses a sub-harmonic, single-bit L1, L2, and L5 sampler that samples at a clock rate of 38.656 MHz. The new capability is the down-conversion and sampling of the L5 signal when previous hardware did not provide this capability. The first GPS IIF Satellite was launched in 2010, providing the new L5 signal. With the JPL SDR flying on the ISS, it will be possible to demonstrate navigation solutions with 10-meter 3-D accuracy at 10-second intervals using a field-program mable gate array (FPGA)-based feedback loop running at 50 Hz. The GPS data bits will be decoded and used in the SDR. The GPSM will also allow other waveforms that are installed in the SDR to demonstrate various GNSS tracking techniques.

Franklin, Garth W.↗
NASA NTRS1998

Thermal Control using Electrochromism

The applicability of a charge balanced electrochromic device to modulate the frequencies in the thermal infrared region is examined in this study. The device consisted of a transparent conductor, WO3 anode, PMMA/LiClO4 electrolyte, V2O5 cathode and transparent conductor. The supporting structure in the device is SnO2 coated glass and the edges are sealed with epoxy to reduce moisture absorption. The performance evaluation comprised of cyclic voltammetric measurements and determination of transmittance at various wavelengths. The device was subjected to anodic and cathodic polarization by sweeping the potential at a rate of 10 mV/sec from -0.8V to 1.8V. The current versus voltage profile indicated no reaction between -0.5 and +0.5 V. The device is colored green at 1.8V with a transmittance of 5% at a wavelength, lambda=900 nm and colorless at -0.8V with a transmittance of 74% at lambda=500 nm. The optical modulation is limited to 400-1500 nm and there is no activity in the thermal infrared. The switching time is 75 seconds for transmittance to decrease from 74% to 50%. The device yielded reproducible values for transmittance when cycled between colored and bleached states by application of 1.8V and -0.8V, respectively.

Vaidyanathan, Hari↗
NASA NTRS1999

Thermal Control Using Electrochromism

The applicability of a charge balanced electrochromic device to modulate the frequencies in the thermal infrared region is examined in this study. The device consisted of a transparent conductor, WO3, anode, PMMA/LiClO4 electrolyte, V2O5 cathode and transparent conductor. The supporting structure in the device is SnO2 coated glass and the edges are sealed with epoxy to reduce moisture absorption. The performance evaluation comprised of cyclic voltammetric measurements and determination of transmittance at various wavelengths. The device was subjected to anodic and cathodic polarization by sweeping the potential at a rate of 10 mV/sec from -0.8V to 1.8V. The current versus voltage profile indicated no reaction between -0.5 and +0.5 V. The device is colored green at 1.8 V with a transmittance of 5% at a wavelength, lambda = 900 nm and colorless at -0.8 V with a transmittance of 74% at lambda = 500 nm. The optical modulation is limited to 400-1500 nm and there is no activity in the thermal infrared. The switching time is a function of temperature and time for coloring reaction was slower than the bleaching reaction. The device yielded reproducible values for transmittance when cycled between colored and bleached states by application of 1.8V and -0.8V, respectively.

Vaidyanathan, Hari↗
NASA NTRS1998

Thermal Control Using Electrochromism

The applicability of a charge balanced electrochromic device to modulate the frequencies in the thermal infra red region is examined in this study. The device consisted of a transparent conductor, WO3 anode, PMMA/LiClO4, electrolyte, V2O5, cathode and transparent conductor. The supporting structure in the device is SnO2 coated glass and the edges are sealed with epoxy to reduce moisture absorption. The performance evaluation comprised of cyclic voltammetric measurements and determination of transmittance at various wavelengths. The device was subjected to anodic and cathodic polarization by sweeping the potential at a rate of 10 mV/sec from -0.8 V to 1.8 V. The current versus voltage profile indicated no reaction between -0.5 and +0.5 V. The device is colored green at 1.8 V with a transmittance of 5% at a wavelength, lambda = 900 nm and colorless at -0.8 V with a transmittance of 74% at X = 500 nm. The optical modulation is limited to 400-1500 nm and there is no activity in the thermal infrared. The switching time is 75 seconds for transmittance to decrease from 74% to 50%. The device yielded reproducible values for transmittance when cycled between colored and bleached states by application of 1.8 V and -0.8 V, respectively.

Vaidyanathan, Hari↗
DOE OSTI2025

Stacked-mosaic amplifier and diode delivery concept for kJ-class inertial fusion energy laser driver

We report on a laser amplifier architecture designed as a modular element for scaling to multi-megajoule laser facilities intended for inertial fusion energy (IFE) power plants. This kilojoule-class module features a stacked mosaic of gain media integrated with a diode delivery system for efficient optical pumping of the mosaic-structured gain medium, enabling high-repetition-rate operation at high wall plug efficiencies, necessary for an IFE driver. Details of a diode delivery system capable of pumping the mosaic architecture are presented. Comprehensive numerical modeling demonstrates that the stacked-mosaic approach reduces transverse gain by five orders of magnitude compared to a conventional full-aperture Yb:YAG based amplifier, substantially suppressing transverse amplified spontaneous emission (TASE) and enabling enhanced longitudinal energy extraction. Detailed analysis of thermal management and wavefront distortion in a 4 × 4 mosaic array indicates that temperature gradients and thermally induced aberrations are effectively controlled using gas cooling and commercially available phase-plate and deformable mirror technologies. We further discuss the applicability of a stacked-mosaic architecture to direct-drive IFE schemes, where broad spectral bandwidth is critical, and its compatibility with frequency conversion modules for up-conversion to blue wavelengths. Finally, an example point design for a 10 kJ, 10 Hz Yb:YAG module operating at 175 K with wall-plug efficiency exceeding 10 % is presented, underscoring the feasibility of this approach for next-generation high-energy lasers for IFE drivers. The results establish the stacked-mosaic amplifier as a scalable, robust platform not only for IFE but also for a broad range of advanced scientific and industrial laser applications.

Lasers↗
DOE OSTI2025

The influence of laser power modulation on melt pool dynamics in laser powder bed fusion

While the majority of laser powder bed fusion (LPBF) metal additive manufacturing uses a continuous wave (CW) laser heat source, some commercial applications of LPBF additive manufacturing instead involve the modulation of the laser power on tens-of-microsecond timescales as an adjustable process variable. This article reports the use of in situ, high speed x-ray and optical imaging to probe melt pool fluid flow, defect formation, and nearby powder motion during LPBF with both modulated and CW laser heat sources. We observe melt pool dynamics unique to modulated laser melting even at very high duty cycles that are related to fluctuations in vapor depression depth, complex pore formation mechanisms, and changes to denudation physics when compared to CW melting. These behaviors are present in Ti–6Al–4V, 316L stainless steel, and AL1100 alloys but vary slightly as a function of material, indicating a substantial dependence on the viscosity and surface tension of the liquid metal. While high duty cycles produce weld tracks of comparable quality to CW melting, lower duty cycles introduce substantial defect concentrations. At intermediate duty cycles, careful control of modulation parameters can repeatably and precisely yield one pore per laser pulse, suggesting a method for intentionally inserting engineered porosity at specific sites during an LPBF build.

3D printing↗
DOE OSTI2025

On-chip frequency-bin quantum photonics

Abstract Frequency-bin encoding furnishes a compelling pathway for quantum information processing systems compatible with established lightwave infrastructures based on fiber-optic transmission and wavelength-division multiplexing. Yet although significant progress has been realized in proof-of-principle tabletop demonstrations, ranging from arbitrary single-qubit gates to controllable multiphoton interference, challenges in scaling frequency-bin processors to larger systems remain. In this Perspective, we highlight recent advances at the intersection of frequency-bin encoding and integrated photonics that are fundamentally transforming the outlook for scalable frequency-based quantum information. Focusing specifically on results on sources, state manipulation, and hyperentanglement, we envision a possible future in which on-chip frequency-bin circuits fulfill critical roles in quantum information processing, particularly in communications and networking.

electro-optic modulators↗
DOE OSTI2025

Vision Foundation Models in Remote Sensing: A survey

Artificial intelligence (AI) technologies have profoundly transformed the field of remote sensing (RS), revolutionizing data collection, processing, and analysis. Traditionally reliant on manual interpretation and task-specific models, RS research has been significantly enhanced by the advent of foundation models (FMs)—large-scale pretrained AI models capable of performing a wide array of tasks with unprecedented accuracy and efficiency. This article provides a comprehensive survey of FMs in the RS domain. We categorize these models based on their architectures, pretraining datasets, and methodologies. Through detailed performance comparisons, we highlight emerging trends and the significant advancements achieved by those FMs. Additionally, we discuss technical challenges, practical implications, and future research directions, addressing the need for high-quality data, computational resources, and improved model generalization. Our research also finds that pretraining methods, particularly self-supervised learning (SSL) techniques like contrastive learning (CL) and masked autoencoders (MAEs), remarkably enhance the performance and robustness of FMs. This survey aims to serve as a resource for researchers and practitioners by providing a panorama of advances and promising pathways for the continued development and application of FMs in RS.

data models↗
DOE OSTI2024

Fragmentation in Gravitationally Unstable Collapsar Disks and Subsolar Neutron Star Mergers

Abstract Although stable neutron stars (NSs) can in principle exist down to massesM ns ≈ 0.1M ⊙ , standard models of stellar core-collapse predict a robust lower limitM ns ≳ 1.2M ⊙ , roughly commensurate with the Chandrasekhar massM Ch of the progenitor’s iron core (electron fractionY e ≈ 0.5). However, this limit may be circumvented in sufficiently dense neutron-rich environments (Y e < 0.5) for which M Ch ∝ Y e 2 is reduced to ≲1M ⊙ . Such physical conditions could arise in the black hole accretion disks formed from the collapse of rapidly rotating stars (“collapsars”), as a result of gravitational instabilities and cooling-induced fragmentation, similar to models for planet formation in protostellar disks. We confirm that the conditions to form subsolar-mass NS (ssNS) may be marginally satisfied in the outer regions of massive neutrino-cooled collapsar disks. If the disk fragments into multiple ssNSs, their subsequent coalescence offers a channel for precipitating subsolar mass LIGO/Virgo gravitational-wave mergers that does not implicate primordial black holes. The model makes several additional predictions: (1) ∼Hz frequency Doppler modulation of the ssNS-merger gravitational-wave signals due to the binary’s orbital motion in the disk; (2) at least one additional gravitational-wave event (coincident within ≲hours), from the coalescence of the ssNS-merger remnant(s) with the central black hole; (3) an associated gamma-ray burst and supernova counterpart, the latter boosted in energy and enriched withr-process elements from the NS merger(s) embedded within the exploding stellar envelope (“kilonovae inside a supernova”).

Astronomy & Astrophysics↗
NASA NTRS1963

The fm demodulator with negative feedback

This paper describes the design and theory of operation of the wideband FM demodulator with feedback (FMFB receiver) used at the Andover, Maine, earth station for Telstar satellite communications tests. Performance data for the FMFB receiver indicate a clear advantage over the conventional FM receiver in many cases. The principal advantage lies in the ability of the FMFB receiver to raise the threshold at which “breaking” occurs for TV and other wideband signals.

TELSTAR SATELLITE↗