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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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The input signal conditioner portion of the multimegasymbol telemetry demodulator and detector feasibility model is described. The input signal conditioner accepts the 55 MHz wideband IF signal of a Block 4 Deep Space Network receiver and provides selectable bandpass filtering, total power automatic gain control, and frequency translation providing inphase and quadrature outputs at baseband.
A study of the dynamic characteristics of a coupled translational-rotational system is given. The formulation of the problem considers the soil-structure interaction effects by utilizing the impedance functions at the foundation of a structure. Due to the fact that the coefficient matrix in the characteristic equation is frequency dependent in nature, iterations have to be performed to find the nature frequencies of the system. Examples and discussions are presented. Comparisons of the analytical results from various approaches are also given.
This disclosure presents a communication receiver system for spacecraft that includes an open loop receiver adapted to receive a communication signal. An ultrastable oscillator (USO) and a tone detector are connected to the open loop receiver. The open loop receiver translates the communication signal to an intermediate frequency signal using a highly stable reference frequency from the USO. The tone detector extracts commands from the communication signal by evaluating the difference between tones of the communication signal.
The Space Life Sciences division (SLSD) concentrates on optimizing a crew member's health. Developments are translated into innovative engineering solutions, research growth, and community awareness. This internship incorporates all those areas by targeting various projects. The main project focuses on integrating clinical and biomedical engineering principles to design, develop, and test new medical kits scheduled for launch in the Spring of 2011. Additionally, items will be tagged with Radio Frequency Interference Devices (RFID) to keep track of the inventory. The tags will then be tested to optimize Radio Frequency feed and feed placement. Research growth will occur with ground based experiments designed to measure calcium encrusted deposits in the International Space Station (ISS). The tests will assess the urine calcium levels with Portable Clinical Blood Analyzer (PCBA) technology. If effective then a model for urine calcium will be developed and expanded to microgravity environments. To support collaboration amongst the subdivisions of SLSD the architecture of the Crew Healthcare Systems (CHeCS) SharePoint site has been redesigned for maximum efficiency. Community collaboration has also been established with the University of Southern California, Dept. of Aeronautical Engineering and the Food and Drug Administration (FDA). Hardware disbursements will transpire within these communities to support planetary surface exploration and to serve as an educational tool demonstrating how ground based medicine influenced the technological development of space hardware.
Niobium-tin has been identified as the most promising next-generation superconducting material for accelerator cavities. This is due to the higher critical temperature (Tc = 18 K) of Nb3Sn compared to niobium (TC = 9.2 K), which leads to greatly reduced RF losses in the cavity during 4.5 K operation. This allows two important changes during cavity and cryomodule design. First, the higher Tc leads to negligible BCS losses when operated at 4.5 K, which allows for a higher frequency to be used, translating to significantly smaller cavities and cryomodules. Second, the reduced dissipated power lowers the required cryogenic cooling capacity, meaning that cavities can feasibly be operated on 5-10 W cryocoolers instead of a centralized helium refrigeration plant. These plants and distribution systems are costly and complex, requiring skilled technicians for operation and maintenance. These fundamental changes present an opportunity for a paradigm shift in how low-beta linacs are designed and operated. Fabrication challenges and first coated cavity test results are discussed.
Nb3Sn has been identified as the most promising next-generation superconducting material for accelerator cavities. This is due to the higher critical temperature (Tc = 18 K) of Nb3Sn compared to niobium (Tc = 9.2 K), which leads to greatly reduced RF losses in the cavity during 4.5 K operation. This allows two important changes during cavity and cryomodule design. First, the higher Tc leads to negligible BCS losses when operated at 4.5 K, which allows for a higher frequency to be used, translating to significantly smaller cavities and cryomodules. Second, the reduced dissipated power lowers the required cryogenic cooling capacity, meaning that cavities can feasibly be operated on 5-10 W cryocoolers instead of a centralized helium refrigeration plant. These plants and distribution systems are costly and complex, requiring skilled technicians for operation and maintenance. These fundamental changes present an opportunity for a paradigm shift in how low-beta linacs are designed and operated. Fabrication and testing results of first prototypes are discussed.
A frequency-tracking feedback circuit for acquiring a communication carrier signal from a relatively noisy environment. The circuit includes a digital phase-frequency detector, a limiter, a mixer, and a voltage-controlled oscillator, connected in a long control loop in such a manner that an input band of signals is translated in frequency until the desired carrier is centered within a relatively narrow acquisition window. The characteristics of the loop are such that acquisition may be achieved even when the total power of the noise in the input signal band exceeds the carrier power, provided that the noise is relatively uniformly distributed over the input band. A technique is also disclosed for compensating from any unbalance in the noise spectrum, so that relatively low carrier-to-noise ratios can be tolerated. Also disclosed are improvements for dynamically varying the parameters of the frequency-tracking loop in such a manner as to reduce acquisition time, and a technique for detecting acquisition and handing control to post-acquisition control circuitry.
Electrification of chemical reactions is crucial to fundamentally transform our society that is still heavily dependent on fossil resources and unsustainable practices. In addition, electrochemistry-based approaches offer a unique way of catalyzing reactions by the fast and continuous alteration of applied potentials, unlike traditional thermal processes. In this work, we show how the continuous cyclic application of electrode potential allows Pt nanoparticles to electrooxidize biomass-derived polyols with turnover frequency improved by orders of magnitude compared with the usual rates at fixed potential conditions. Moreover, secondary alcohol oxidation is enhanced, with a ketoses-to-aldoses ratio increased up to sixfold. The idea has been translated into the construction of a symmetric single-compartment system in a two-electrode configuration. Its operation via voltage cycling demonstrates high-rate sorbitol electrolysis with the formation of H 2 as a desired coproduct at operating voltages below 1.4 V. The devised method presents a potential approach to using renewable electricity to drive chemical processes.
This work proposes a three-stage converter topology with a medium frequency isolation transformer for direct integration of energy storage systems into medium voltage distribution grids. The distributed architecture of the topology, using standard AC/DC converters, has been developed with the aim of plug-and-play capability and voltage and power scalability. The medium frequency transformer facilitates improved power density, while its 20:1 voltage translation capability enables the use of limited voltage level (500 Vdc) of the commercially available batteries. This paper presents the topology structure and details how it can be scaled to reach the full range of the distribution grid voltages and the required power levels. A transformer design for 500 Hz rated frequency is discussed. The control scheme of the converter equipped with voltage support, frequency support, and black start capabilities is also presented. Control hardware-in-the-loop results using OPAL-RT, with converter switching models connected to a weak IEEE-4 node test feeder modified for the aforementioned grid services, are provided to show the topology feasibility.
The air-water and graphene-water interfaces represent quintessential examples of the liquid-gas and liquid-solid boundaries, respectively. While the sum-frequency generation (SFG) spectra of these interfaces show similarities, a consensus on their signals and interpretations has yet to be reached. Leveraging deep learning, we computed first-principles SFG spectra for both systems, addressing experimental discrepancies. Here, our findings reveal that similarities in SFG signals do not translate into comparable interfacial microscopic properties. Instead, graphene-water and air-water interfaces exhibit fundamental differences in SFG-active thicknesses, hydrogen-bonding networks, and surface dynamics. These distinctions underscore roughness suppression and electronic interactions present at the solid-liquid interface but absent at the gas-liquid interface.
Thin cirrus clouds (with optical depth tau much less than 1) play a potentially important role in the Earth atmosphere. The Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra satellite has a channel at 1.375 microns that is specifically designed to detect these clouds. During two three-day periods from December 2000 and June 2001, I show that thin cirrus clouds are ubiquitous throughout the tropics. These thin cirrus generally have optical depths below 0.05 and appear with greater frequency and optical depth near deep convection. Regressing top-of-atmosphere outgoing longwave flux data from the Clouds and the Earth's Radiant Energy System (CERES) against optical depth, we calculate that these thin clouds decrease outgoing longwave flux by approx. 1 W/sq m/(0.01 tau). This translates into longwave forcing of several W/sq m near convection and zero away from convection. Averaging over the whole tropics, these thin cirrus decrease average longwave forcing is approx. 1.4 W/sq m.
Traditional theories of the nuclear magnetic resonance (NMR) autocorrelation function for intra-molecular dipole pairs assume a single-exponential decay, yet the calculated autocorrelation of realistic systems displays a rich, multi-exponential behavior, resulting in anomalous NMR relaxation dispersion (i.e., frequency dependence). We develop an approach to model and interpret the multi-exponential intra-molecular autocorrelation using simple, physical models within a rigorous statistical mechanical development that encompasses both rotational diffusion and translational diffusion in the same framework. Here, we recast the problem of evaluating the autocorrelation in terms of averaging over a diffusion propagator whose evolution is described by a Fokker–Planck equation. The time-independent part admits an eigenfunction expansion, allowing us to write the propagator as a sum over modes. Each mode has a spatial part that depends on the specified eigenfunction and a temporal part that depends on the corresponding eigenvalue (i.e., correlation time) with a simple, exponential decay. The spatial part is a probability distribution of the dipole pair, analogous to the stationary states of a quantum harmonic oscillator. Drawing inspiration from the idea of inherent structures in liquids, we interpret each of the spatial contributions as a specific molecular mode. These modes can be used to model and predict the NMR dipole–dipole relaxation dispersion of fluids by incorporating phenomena on the molecular level. We validate our statistical mechanical description of the distribution in molecular modes with molecular dynamics simulations interpreted without any relaxation models or adjustable parameters: the most important poles in the Padé–Laplace transform of the simulated autocorrelation agree with the eigenvalues predicted by the theory
The control of flexible spacecraft is a difficult problem because of large number of elastic modes; low value, closely-spaced frequencies; very small damping; and uncertainties in math models. The traditional design approach is to design the structure first and then to design the control system. This view-graph presentation develops a methodology for spacecraft design which addresses control/structure interaction issues, produces technology for simultaneous control/structure design, and translates into algorithms and computational tools for practical integrated computer-aided design.
Despite being a staple of synthetic plastics and biomolecules, helical polymers are scarcely studied with Gaussian-basis-set ab initio electron-correlated methods on an equal footing with molecules. This article introduces an ab initio second-order many-body Green’s-function [MBGF(2)] method with nondiagonal, frequency-dependent Dyson self-energy for infinite helical polymers using screw-axis-symmetry-adapted Gaussian-spherical-harmonics basis functions. Together with the Gaussian-basis-set density-functional theory for energies, analytical atomic forces, translational-period force, and helical-angle force, it can compute correlated energy, quasiparticle energy bands, structures, and vibrational frequencies of an infinite helical polymer, which smoothly converge at the corresponding oligomer results. These methods can handle incommensurable structures, which have an infinite translational period and are hard to characterize by any other method, just as efficiently as commensurable structures. We apply them to polyethylene (2/1 helix), polyacetylene (Peierls’ system), and polytetrafluoroethylene (13/6 helix) to establish the quantitative accuracy of MBGF(2)/cc-pVDZ in simulating their (angle-resolved) ultraviolet photoelectron spectra, and of B3LYP/cc-pVDZ or 6-31G** in reproducing their structures, infrared and Raman band positions, phonon dispersions, and (coherent and incoherent) inelastic neutron scattering spectra. We then predict the same properties for infinitely catenated chains of nitrogen or oxygen and discuss their possible metastable existence under ambient conditions. They include planar zigzag polyazene (N2)x (Peierls’ system), 11/3-helical isotactic polyazane (NH)x, 9/4-helical isotactic polyfluoroazane (NF)x, and 7/2-helical polyoxane (O)x as potential high-energy-density materials.
The Space Technology 7 experiment will perform an on-orbit system-level validation of two specific Disturbance Reduction System technologies: a gravitational reference sensor employing a free-floating test mass and a set of micronewton colloidal thrusters. The Disturbance Reduction System is designed to maintain a spacecraft's position with respect to the free-floating test mass to less than 10 nm/square root of Hz, over the frequency range 10(exp -3) Hz to 10(exp -2) Hz. This paper presents the design and analysis of the coupled drag-free and attitude control system that closes the loop between the gravitational reference sensor and the micronewton thrusters while incorporating star tracker data at low frequencies. The effects of actuation and measurement noise and disturbances on the spacecraft and test masses are evaluated in a seven-degree-of-freedom planar model incorporating two translational and one rotational degrees of freedom for the spacecraft and two translational degrees of freedom for each test mass.
This report reviews the scientific literature regarding the human system risks to the microgravity environment of space flight in relation to human performance. The primary human performance-related risks involve deconditioning of the cardiovascular and skeletal muscles systems due to prolonged exposure to the reduced gravitational input. The chronological history of U.S. space flight is reviewed as a starting point to inform and understand the gaps in the knowledge to these risks. Maintenance of physical performance capabilities involves understanding the health of many organ systems (peripheral [vascular, heart, blood volume, skeletal muscle] and central [brain]) that ultimately contribute to the submaximal and maximal capacity of the aerobic (VO2peak), skeletal muscle (strength and endurance) systems. Maintaining astronaut VO2peak, muscle mass, strength, and endurance before, during, and after space flight is a significant priority to NASA for the current International Space Station (ISS) era, as well as for future exploration missions. A growing research database from both space flight and ground-based analog studies finds that the cardiorespiratory system is compromised and skeletal muscles (predominantly postural muscles of the lower limbs) undergo atrophy. These structural and metabolic responses to living in microgravity conditions contribute to physiological deconditioning during space flight that potentially increase the risks to astronauts returning to surface operations (i.e., Moon, Mars, or Earth). The time course changes from short to long-duration space flight and the relationships between in-flight performance deconditioning levels are not well characterized. Moreover, there are large interindividual variabilities that may be dependent on genetics, age, sex, preflight fitness levels, and individual exercise prescriptions that need further careful evaluations. Efforts should be made to understand the current status of preflight, in-flight, and postflight exercise performance capability and to define the operational goals and target areas for protection with the in-flight exercise program. There is a bi-directional relationship between exercise prescription and hardware countermeasures that need further understanding in-flight. For example, hardware with limited capabilities/modalities may be counterbalanced by changes in exercise prescription (i.e., frequency, time, intensity, volume) for providing effective responses to maintain fitness. Importantly, the minimal requirements for exercise prescription on ISS hardware may not translate to lower capability hardware on exploration missions. Due to limited volume on exploration vehicles, future Artemis missions to the Lunar surface will not have similar exercise hardware capabilities as ISS. This may alter the effectiveness of hardware to provide adequate physiological stress on bodily systems allowing for adaptations to maintain aerobic capacity, strength, and bone density. Thus, it will be important to understand the exercise responses of current ISS countermeasures to develop individualized exercise prescriptions that minimize aerobic and muscular risks, accounting for the large variability of responses among crewmembers. Newer exploration exercise hardware is currently being evaluated that is more compact (i.e., E4D and Orion Flywheel) and will require careful evaluation of the hardware on the stressor (i.e., metabolic rate, oxygen uptake, and heart rate work relationships, and force plate load profiles) needed the human body to protect and maintain crew health and performance. Moreover, exercise responses on the hardware need careful evaluation on the chronic adaptations. Lastly, in-flight evaluation of hardware exercise response may differ in 0-g or partial-g compared to 1-g. Therefore, it cannot be assumed that the stress on the body will be the same in each environment. Understanding this has a direct impact on exercise prescriptions. This document provides an overview of key scientific investigations that have been conducted before, during, and after human space flight missions, as well as from human ground-based analog studies that contribute to the evidence base on changes in aerobic capacity and muscle mass, strength, and endurance. Additional data from rodent and nonhuman primate experiments of skeletal muscle unloading completed during space flight or ground-based flight-simulations provide supportive information about this risk topic. Most importantly, a recent, large dataset from long-duration ISS crew has been added to give improved insight into the variability of exercise response of crew, demonstrating that a large portion of the crew population return to Earth with greater than 10-20% loss of aerobic capacity and muscle strength and endurance. Data from human space flight and ground-based studies are narrowing in on the required exercise paradigms but thus far still provide an incomplete answer to an effective approach for maintaining skeletal muscle function and aerobic fitness of all human space travelers. Finally, the relationship of this risk topic to various space flight operational scenarios is examined and discussed.
Head movements in the sagittal pitch plane typically involve off-axis rotation requiring both vertical and horizontal vergence ocular reflexes to compensate for angular and translational motion relative to visual targets of interest. The purpose of this study was to compare passive pitch VOR responses during rotation about an Earth-vertical axis (canal only cues) with off-axis rotation (canal and otolith cues). Methods. Eleven human subjects were oscillated sinusoidally at 0.13, 0.3 and 0.56 Hz while lying left-side down with the interaural axis either aligned with the axis of rotation or offset by 50 cm. In a second set of measurements, twelve subjects were also tested during sinusoidally varying centrifugation over the same frequency range. The modulation of vertical and horizontal vergence ocular responses was measured with a binocular videography system. Results. Off-axis pitch rotation enhanced the vertical VOR at lower frequencies and enhanced the vergence VOR at higher frequencies. During sinusoidally varying centrifugation, the opposite trend was observed for vergence, with both vertical and vergence vestibulo-ocular reflexes being suppressed at the highest frequency. Discussion. These differential effects of off-axis rotation over the 0.13 to 0.56 Hz range are consistent with the hypothesis that otolith-ocular reflexes are segregated in part on the basis of stimulus frequency. At the lower frequencies, tilt otolith-ocular responses compensate for declining canal input. At higher frequencies, translational otolith-ocular reflexes compensate for declining visual contributions to the kinematic demands required for fixating near targets.
Time-varying optical media, whose dielectric properties are actively modulated in time, introduce a host of novel effects in the classical propagation of light, and are of intense current interest. In the quantum domain, time-dependent media can be used to convert vacuum fluctuations (virtual photons) into pairs of real photons. Here, we refer to these processes broadly as “dynamical vacuum effects” (DVEs). Despite interest for their potential applications as sources of quantum light, DVEs are generally very weak, presenting many opportunities for enhancement through modern techniques in nanophotonics, such as using media which support excitations such as plasmon and phonon polaritons. Here, we present a theory of weakly modulated DVEs in arbitrary nanostructured, dispersive, and dissipative systems. A key element of our framework is the simultaneous incorporation of time-modulation and “dispersion” through time-translation-breaking linear response theory. As an example, we use our approach to propose a highly efficient scheme for generating entangled surface polaritons based on time-modulation of the optical phonon frequency of a polar insulator.