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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Evaluation of Acoustic Propagation in Layered Media Using Wave Confinement

A comprehensive method for propagation of sound in layered media is discussed that involves dividing the domain into two regions, source field and far field. The source field is provided using experimentally collected data from full-scale rotorcraft acoustic flight tests, which consists of short waveforms that cannot be directly simulated on the grid without numerical errors. Instead, grid based computational waves are used to carry the details of these waveforms, including amplitude, arrival time and location of origin on source sphere. This is done by solving the scalar wave equation using the Wave Confinement (WC) method, which involves adding an extra term to produce converged solutions. WC is used to study wave propagation in two different atmospheric conditions, and the results are compared to the flight test data. Overall, WC can accurately capture the propagation effects and there is a good agreement with the flight test data.

rotorcraft acoustics↗
NASA NTRS2022

Space Induced Discharge Model to Be Used on Interface Circuit Vulnerability Assessment

Charging can occur in space due to plasma and high energy particles. Charging is especially severe in certain earth orbits such as geostationary orbit, medium earth orbit and highly inclined orbit. A spacecraft that travels to other planets such as Jupiter also encounters high level of charging due to Jupiter’s radiation belt. The major concern for spacecraft operation due to charging is the survival of sensitive electrical circuits. Dielectrics and floating metal can charge up and discharge onto interface circuits. The electrical circuits need to be evaluated for survival from the electrostatic-discharge (ESD) threat. Both ESD induced upset and damage need to be assessed. The interface circuits are often located inside a shielded unit in the spacecraft structure or a shielded vault with sufficient radiation shielding to avoid surface and internal charging. The materials external to the highly shielded area can charge up and discharge onto wires that can directly dissipate the ESD onto the interface circuits. Figure 1 shows a possible discharge mechanism onto the interfacing circuits. If the wire has an external shield or a coaxial line, some or most of the discharge can flow on the shield to chassis ground. There is always coupling from external discharge. If the wire has no shield, the discharge flows onto the interface circuit. Fig. 1 Possible discharge paths onto the interface circuits. The purpose of this article is to address how to model the ESD threat to be used as the discharge source onto the interface circuit based on the electron beam test data. Different models are needed for different impedances associated with the interface circuits. Once those models are derived, one needs to analyze the interface circuit with the corresponding model using an electrical simulation tool. Then, the circuit’s front-end components can be assessed for damage and upset. Upset is highly dependent on the circuit operation and system requirements, and thus it is not addressed any further. Damage of electrical parts is often rated under Human-Body-Model (HBM) ESD. One can utilize this industry-wide available information to assess the damage vulnerability due to space discharges. However, the HBM waveform does not always match the discharge waveform. To estimate the damage vulnerability of the circuit and set margin, one needs to compare the equivalent energy delivered to the victim between a HBM discharge and the results from an ESD source model based on actual discharges. This paper presents such a comparison for a few select cases.

Xie, Julie↗
NASA NTRS2023

Estimating the Noise Dose Range of the NASA X-59 Aircraft in Supersonic Cruise Using PCBoom Propagation Simulations

PCBoom propagation simulations of the NASA X-59 low-boom in supersonic cruise were conducted using near-field CFD pressure waveforms as inputs to estimate the noise dose range. Low-booms were propagated through realistic atmospheric profiles from the Climate Forecast System Version 2 across the USA, and loudness statistics of the low-booms are presented. The near-field waveforms correspond to aircraft configurations expected to produce minimum- and maximum-loudness levels on the ground. The simulations show that the practical Perceived Level noise dose range is 72 to 86.7 dB. Dose ranges for other single event and cumulative sonic boom metrics of interest are also provided.

X-59↗
NASA NTRSDate not supplied

Development and Airborne Demonstration of the Concurrent Artificially-Intelligent Spectrometry and Adaptive Lidar System: Advancing Lidar Capabilities for the STV Observing System

We report on the design, build and planned airborne demonstration of a spaceflight-prototype Concurrent Artificially-intelligent Spectrometry and Adaptive Lidar System (CASALS). The CASALS lidar is an Adaptive Wavelength Scanning Lidar (AWSL) operating in push broom mode. The demonstration has three major goals: advance the Technical Readiness Level of the AWSL hardware, validate its measurement performance and mature algorithms and methods needed for the Surface Topography and Vegetation (STV) observing system. AWSL acquires parallel tracks of surface heights by rapidly steering a laser beam across a swath. A 1040nm-centered laser is tuned across 30nm and carved into 2-ns pulses, the pulse energy is fiber amplified and the pulses are dispersed cross-track using a non-mechanical wavelength-to-angle grating. For the spaceflight system the beam will be pointable to 1200 10m footprints across a 7km swath. For the airborne demonstration there will be 256 0.7m footprints across a 110m swath. In both cases the footprints overlap across- and along-track for uniform target illumination. For the airborne demonstration a steering mirror will increase the accessible swath width to 4km. At the receiver, solar radiation is filtered with a narrow-slit grating-spectrometer and the footprints are imaged onto a linear-mode, photon-sensitive HgCdTe APD-array. The received pulses are time-division-multiplexed to a few high-speed analog-to-digital converters to record waveforms. Spaceflight and airborne CASALS are designed to nominally detect 20 photons per pulse and, by averaging 27 overlapping footprints, achieve 2cm flat target range precision and high-quality vegetation structure waveforms The AWSL will be flown in the summer of 2024, along with a Headwall VNIR-SWIR hyperspectral sensor imaging a 4km wide swath, at NEON eddy covariance flux towers in the U.S. mid-Atlantic where high resolution hyperspectral and lidar data, acquired annually, are available for validation.

Guangning Yang↗
NASA NTRS2024

Spectrally Efficient GaN High-Power Amplifier for Lunar Communications

The paper demonstrates a spectrally efficient Ka-band GaN MMIC based high-power amplifier (HPA) that uses a waveguide 4-port magic-tee as a 2-way power combiner to combine the output from two lower power amplifier circuits. The paper presents for the prototype HPA the measured output power, gain, power added efficiency, error vector magnitude for Offset-QPSK, 8PSK, 16APSK, 32APSK, and 16QAM waveforms, waveform spectrum, and out-of-band spectral regrowth. The HPA is intended for establishing a direct communication link between assets on the lunar surface/orbit and Earth.

Gallium nitride↗
NASA NTRS2025

Uncertainty Quantification for Empirical X-59 Sonic Boom Loudness Levels

Estimates of the total uncertainty for empirically determined loudness levels are documented when GRS (Ground Recording System) noise monitors are used to record X 59 sonic boom waveforms. The total uncertainty is characterized by combining nine different sources of uncertainty that may affect the apparent gain of the measurement chain. These uncertainty estimates are presented as expected measurement error relative to the true loudness level, and separate error estimates are provided for eight different noise metrics in which NASA has interest. The behavior of the Perceived Level (PL) metric is studied within the report body, while the total uncertainties for the seven other noise metrics are summarized in appendices for brevity. The effects of four sources of uncertainty are estimated simply from information found on hardware specification sheets provided by the manufacturer. However, mock acoustic recordings are created to estimate the effects of other sources because those effects are expected to induce spectral coloration, so they may vary with noise metric type and sound level. These sources are not well modeled by simple gain adjustments. Importantly, measurement error is computable when processing mock recordings since the true levels are knowable, which is not the case when processing data recorded in the field. Specifically, the true levels are knowable because the components of the mock recordings are separable – e.g., loudness levels of booms can be computed with or without superimposed background noise. Mock acoustic recordings also have the benefit of allowing analysis of sonic booms from vehicles that are not yet flying, like the X-59, since the mock recordings are created by combining vehicle-specific predicted waveforms with other audio sources. The estimates of total measurement error are documented as a function of the signal-to-noise ratio (SNR) of the loudness level, where the corrected SNR is computed while accounting for the effects of the method that is used to correct for background noise contamination when computing the noise metric values. The corrected SNR calculations used here can be applied to both mock recordings and in-field measurements, so the uncertainty of in-field recordings can be found using pre-computed lookup tables that identify the relationship between metric type, corrected SNR, and the expected measurement error.

Sonic Boom↗
NASA NTRS2005

The 26 December 2004 tsunami source estimated from satellite radar altimetry and seismic waves

The 26 December 2004 Indian Ocean tsunami was the first earthquake tsunami of its magnitude to occur since the advent of both digital seismometry and satellite radar altimetry. Both have independently recorded the event from different physical aspects. The seismic data has then been used to estimate the earthquake fault parameters, and a three-dimensional ocean-general-circulation-model (OGCM) coupled with the fault information has been used to simulate the satellite-observed tsunami waves. Here we show that these two datasets consistently provide the tsunami source using independent methodologies of seismic waveform inversion and ocean modeling. Cross-examining the two independent results confirms that the slip function is the most important condition controlling the tsunami strength, while the geometry and the rupture velocity of the tectonic plane determine the spatial patterns of the tsunami.

ocean general circulation model (OGCM)↗
NASA NTRS2014

Evaluation of the Performance Characteristics of the CGLSS and NLDN Systems Based on Two Years of Ground-Truth Data from Launch Complex 39B, Kennedy Space Center, Florida

From May 2011 through July 2013, the lightning instrumentation at Launch Complex 39B (LC39B) at the Kennedy Space Center, Florida, has obtained high-speed video records and field change waveforms (dE/dt and three-axis dH/dt) for 54 negative polarity return strokes whose strike termination locations and times are known with accuracy of the order of 10 m or less and 1 μs, respectively. A total of 18 strokes terminated directly to the LC39B lighting protection system (LPS), which contains three 181 m towers in a triangular configuration, an overhead catenary wire system on insulating masts, and nine down conductors. An additional 9 strokes terminated on the 106 m lightning protection mast of Launch Complex 39A (LC39A), which is located about 2.7 km southeast of LC39B. The remaining 27 return strokes struck either on the ground or attached to low-elevation grounded objects within about 500 m of the LC39B LPS. Leader/return stroke sequences were imaged at 3200 frames/sec by a network of six Phantom V310 high-speed video cameras. Each of the three towers on LC39B had two high-speed cameras installed at the 147 m level with overlapping fields of view of the center of the pad. The locations of the strike points of 54 return strokes have been compared to time-correlated reports of the Cloud-to-Ground Lightning Surveillance System (CGLSS) and the National Lightning Detection Network (NLDN), and the results of this comparison will be presented and discussed.

Waveforms↗
NASA NTRS2016

Variable Coding and Modulation Experiment Using NASA's Space Communication and Navigation Testbed

National Aeronautics and Space Administration (NASA)'s Space Communication and Navigation Testbed on the International Space Station provides a unique opportunity to evaluate advanced communication techniques in an operational system. The experimental nature of the Testbed allows for rapid demonstrations while using flight hardware in a deployed system within NASA's networks. One example is variable coding and modulation, which is a method to increase data-throughput in a communication link. This paper describes recent flight testing with variable coding and modulation over S-band using a direct-to-earth link between the SCaN Testbed and the Glenn Research Center. The testing leverages the established Digital Video Broadcasting Second Generation (DVB-S2) standard to provide various modulation and coding options. The experiment was conducted in a challenging environment due to the multipath and shadowing caused by the International Space Station structure. Performance of the variable coding and modulation system is evaluated and compared to the capacity of the link, as well as standard NASA waveforms.

waveforms↗
NASA NTRS2016

Adaptive Coding and Modulation Experiment With NASA's Space Communication and Navigation Testbed

National Aeronautics and Space Administration (NASA)'s Space Communication and Navigation Testbed is an advanced integrated communication payload on the International Space Station. This paper presents results from an adaptive coding and modulation (ACM) experiment over S-band using a direct-to-earth link between the SCaN Testbed and the Glenn Research Center. The testing leverages the established Digital Video Broadcasting Second Generation (DVB-S2) standard to provide various modulation and coding options, and uses the Space Data Link Protocol (Consultative Committee for Space Data Systems (CCSDS) standard) for the uplink and downlink data framing. The experiment was con- ducted in a challenging environment due to the multipath and shadowing caused by the International Space Station structure. Several approaches for improving the ACM system are presented, including predictive and learning techniques to accommodate signal fades. Performance of the system is evaluated as a function of end-to-end system latency (round- trip delay), and compared to the capacity of the link. Finally, improvements over standard NASA waveforms are presented.

waveforms↗
NASA NTRS2017

A COTS RF/Optical Software Defined Radio for the Integrated Radio and Optical Communications Test Bed

The Integrated Radio and Optical Communications (iROC) project at the National Aeronautics and Space Administration (NASA) is investigating the merits of a hybrid radio frequency (RF) and optical communication system for deep space missions. In an effort to demonstrate the feasibility and advantages of a hybrid RF/Optical software defined radio (SDR), a laboratory prototype was assembled from primarily commercial-off-the-shelf (COTS) hardware components. This COTS platform has been used to demonstrate simultaneous transmission of the radio and optical communications waveforms through to the physical layer (telescope and antenna). This paper details the hardware and software used in the platform and various measures of its performance. A laboratory optical receiver platform has also been assembled in order to demonstrate hybrid free space links in combination with the transmitter.

waveforms↗
NASA NTRS2016

An Optical Receiver Post-Processing System for the Integrated Radio and Optical Communications Software Defined Radio Test Bed

The Integrated Radio and Optical Communications (iROC) project at the National Aeronautics and Space Administration's (NASA) Glenn Research Center is investigating the feasibility of a hybrid radio frequency (RF) and optical communication system for future deep space missions. As a part of this investigation, a test bed for a radio frequency (RF) and optical software defined radio (SDR) has been built. Receivers and modems for the NASA deep space optical waveform are not commercially available so a custom ground optical receiver system has been built. This paper documents the ground optical receiver, which is used in order to test the RF and optical SDR in a free space optical communications link.

optical communication↗
NASA NTRS2016

A COTS RF Optical Software Defined Radio for the Integrated Radio and Optical Communications Test Bed

The Integrated Radio and Optical Communications (iROC) project at the National Aeronautics and Space Administration (NASA) is investigating the merits of a hybrid radio frequency (RF) and optical communication system for deep space missions. In an effort to demonstrate the feasibility and advantages of a hybrid RFOptical software defined radio (SDR), a laboratory prototype was assembled from primarily commercial-off-the-shelf (COTS) hardware components. This COTS platform has been used to demonstrate simultaneous transmission of the radio and optical communications waveforms through to the physical layer (telescope and antenna). This paper details the hardware and software used in the platform and various measures of its performance. A laboratory optical receiver platform has also been assembled in order to demonstrate hybrid free space links in combination with the transmitter.

waveforms↗
NASA NTRS2016

An Optical Receiver Post Processing System for the Integrated Radio and Optical Communications Software Defined Radio Test Bed

The Integrated Radio and Optical Communications (iROC) project at the National Aeronautics and Space Administrations (NASA) Glenn Research Center is investigating the feasibility of a hybrid radio frequency (RF) and optical communication system for future deep space missions. As a part of this investigation, a test bed for a radio frequency (RF) and optical software defined radio (SDR) has been built. Receivers and modems for the NASA deep space optical waveform are not commercially available so a custom ground optical receiver system has been built. This paper documents the ground optical receiver, which is used in order to test the RF and optical SDR in a free space optical communications link.

waveforms↗