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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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Digital voltage-controlled oscillator generates a variable frequency signal controlled linearly about a center frequency with high stability and is phase controlled by an applied voltage. Integration ahead of the digital circuitry provides linear operation with control voltage having appreciable noise components.
Development of attitude control system for sounding rocket stabilization during ballistic phase of flight
Analysis of specific problems in rotorcraft dynamics. Topics include hingeless rotor theory, dynamic stall modelling, periodic systems identification, analysis of complex systems with phasing matrices, flapping stability, flap-lag dynamics at high advance ratios, finite element analysis and fuselage free-vibration characteristics, coupled rotor/frame vibration methods, gust response characteristics with unsteady stall effects, antiresonance theory, cyclic feathering motions and dynamic loads, control load envelope shaping, rotor aeroelasticity, use of Floquet theory, theory of proprotors and tilt-rotors, two-bladed teetering rotors, stability of air and ground resonance, vertical-plane pendulum absorbers, multicyclic jet-flap control, engine/frame interface dynamics, and others. The minutes of the question and answer periods following the presentations are presented in the supplement. Individual items are announced in this issue.
The fundamental processes controlling lean combustion were observed for better understanding, with particular emphasis on the formation and measurement of gas-phase pollutants, the stability of the combustion process (blowout limits), methods of improving stability, and the application of probe and optical diagnostics for flow field characterization, temperature mapping, and composition measurements. The following areas of investigation are described in detail: (1) axisymmetric, opposed-reacting-jet-stabilized combustor studies; (2) stabilization through heat recirculation; (3) two dimensional combustor studies; and (4) spectroscopic methods. A departure from conventional combustor design to a premixed/prevaporized, lean combustion configuration is attractive for the control of oxides of nitrogen and smoke emissions, the promotion of uniform turbine inlet temperatures, and, possibly, the reduction of carbon monoxide and hydrocarbons at idle.
Viking data suggest the presence of volatile-rich materials in the Martian regolith. The thermal stabilities of mineral phases and their volatile release profiles were studied in detail in our laboratory. Thermal analysis, combined with mass spectrometry, was applied to the study of the behavior of carbonates, sulfates, hydrates, and clays. The results indicate that these techniques are useful in the preliminary mineralogical characterizations of volatile-rich minerals. However, our results also indicate that great care must be taken in the incorporation into planetary probes of such methods as hearing rates, pressure, composition of atmospheres, grain size, etc., because these factors effect volatile release.
The role of cobalt in a representative wrought nickel-base superalloy was determined. The results show cobalt affecting the solubility of elements in the gamma matrix, resulting in enhanced gamma' volume fraction, in the stabilization of MC-type carbides, and in the stabilization of sigma phase. In the particular alloy studied, these microstructural and microchemistry changes are insufficient in extent to impact on tensile strength, yield strength, and in the ductilities. Depending on the heat treatment, creep and stress rupture resistance can be cobalt sensitive. In the coarse grain, fully solutioned and aged condition, all of the alloy's 17% cobalt can be replaced by nickel without deleteriously affecting this resistance. In the fine grain, partially solutioned and aged condition, this resistance is deleteriously affected only when one-half or more of the initial cobalt content is removed. The structure and property results are discussed with respect to existing theories and with respect to other recent and earlier findings on the impact of cobalt, if any, on the performance of nickel-base superalloys.
The four particular classes of premixed flames which are of special interest include freely propagating gaseous flames, burner stabilized premixed gaseous flames, freely propagating particle-cloud flames, and burner stabilized two-phase flames. Associated gravitational effects are related to upward flame propagation, downward flame propagation, and flame propagation in microgravity. The results of theoretical and experimental studies suggest that a comprehensive approach to representation of extinction limits must deal with the full range of existence limits observed for flames. Issues awaiting solution are related to the flammability limits, extinction limit relations, and flame theories for g = 0. Attention is given to theoretical considerations, nonadiabatic features of premixed lycopodium-air flames, and general comments on the extinction conditions for premixed flames.
Different approaches that are being utilized to test laser optical systems are described. One of the most crucial areas in the testing phase is the stability of the laser optics mounted inside the space simulator. The thermal vacuum system, the refrigeration system, and the space simulator are discussed.
The feasibility of enhancing neurocontrol robustness, through training of the neurocontroller and state estimator in the presence of system uncertainties, is investigated on the example of a multivariable aircraft control problem. The performance and robustness of the newly trained neurocontroller are compared to those for an existing neurocontrol design scheme. The newly designed dynamic neurocontroller exhibits a better trade-off between phase and gain stability margins, and it is significantly more robust to degradations of the plant dynamics.
Tl-Ba-Cu-Cu-O superconducting thin films were prepared by magnetron sputtering with postannealing in a reduced oxygen atmosphere. Single-phase Tl2Ba2Ca2Cu3O(x) can form on the MgO substrate at 800 C under P(O2) about 0.1 atm. However the phase formation temperature can be affected by the starting composition of the film. Tl1Ba2Ca2Cu3O(x) phase can be formed by simply lowering the Tl2O pressure. The thermal stability of Tl1Ba2Ca2Cu3O(x) phase was studied by resistivity measurements at high temperatures.
The Frequency Standards Laboratory at the Jet Propulsion Laboratory (JPL) is responsible for the generation and distribution of ultra-stable reference frequency in NASA's Deep Space Network (DSN). Certain assemblies and components of the Radio Science and VLBI systems are located in the cones of tracking antennas hundreds of meters from the Frequency and Timing Subsystem's frequency standards. The very stringent requirements of these users challenge the performance of state-of-the-art frequency sources as well as the associated signal distribution system. The reference frequency distribution system described is designed around a low temperature coefficient of delay (TCD) optical fiber. On-site measurements of the fiber optic link alone indicate 100 MHz phase noise performance on the order of -120 dBc at 1 Hz from the carrier and Allan deviation on the order of parts in 10(exp 16) at 1000 seconds averaging time. The measured phase noise and stability of the link indicate that the performance characteristics of the hydrogen maser frequency standards are not degraded by the distribution system. Thus, optical fibers and electro-optic devices as distribution media appear to be a viable alternative to the classical coaxial cable distribution systems.
To understand how the solar system formed we must understand the compositional distribution of the current system. Volatile species are particularly important in that their stability as condensed phases is limited in temperature-pressure space, and hence variations in their distribution at present potentially contain an imprint of processes by which temperature and pressure varied in the solar nebula. In this talk we restrict ourselves to species more volatile than water ice, and address issues related to processes in the outer solar system and the formation of bodies there; others in this conference will cover volatile species relevant to inner solar system processes. Study of the outer solar system is relevant both to understanding the interface between the solar nebula and the progenitor giant molecular cloud (since the chemical links to present-day observables in molecular clouds are species like methane, carbon monoxide, etc.), as well as the origin of terrestrial planet atmospheres and oceans (the latter to be covered by Owen). The wealth of compositional information on outer solar system bodies which has become available from spacecraft and ground-based observations challenges traditional simplistic views of the composition and hence dynamics of the solar nebula. The basic assumption of thermochemical equilibrium, promulgated in the 1950's, in which methane and ammonia dominate nitrogen- and carbon-bearing species, is demonstrably incorrect on both observational and theoretical grounds. However, the kinetic inhibition model which replaced it, in which carbon monoxide and molecular nitrogen dominate a nebula which is fully mixed and hence cycles outer solar system gases through a hot, chemically active zone near the disk center, is not supported either by observations. Instead, a picture of the outer solar system emerges in which the gas and grains are a mixture of relatively unaltered, or modestly altered, molecular cloud material, along with a fraction which has been chemically altered in the solar nebula itself (and perhaps giant planet nebulae).
Nucleation rates in condensed systems are frequently not at their steady state values. Such time dependent (or transient) nucleation is most clearly observed in devitrification studies of metallic and silicate glasses. The origin of transient nucleation and its role in the formation and stability of desired phases and microstructures are discussed. Numerical models of nucleation in isothermal and nonisothermal situations, based on the coupled differential equations describing cluster evolution within the classical theory, are presented. The importance of transient nucleation in glass formation and crystallization is discussed.
An all-solid-state replacement for high-frequency Gunn diode oscillators (GDOs) has been proposed for use in NASA s millimeter- and submillimeter-wave sensing instruments. Highly developed microwave oscillators are used to achieve a low-noise and highly stable reference signal in the 10-40-GHz band. Compact amplifiers and high-power frequency multipliers extend the signal to the 100-500-GHz band with minimal added phase noise and output power sufficient for NASA missions. This technology can achieve improved output power and frequency agility, while maintaining phase noise and stability comparable to other GDOs. Additional developments of the technology include: a frequency quadrupler to 145 GHz with 18 percent efficiency and 15 percent fixed tuned bandwidth; frequency doublers featuring 124, 240, and 480 GHz; an integrated 874-GHz subharmonic mixer with a mixer noise temperature of 3,000 K DSB (double sideband) and mixer conversion loss of 11.8 dB DSB; a high-efficiency frequency tripler design with peak output power of 23 mW and 14 mW, and efficiency of 16 and 13 percent, respectively; millimeter-wave integrated circuit (MMIC) power amplifiers to the 30-40 GHz band with high DC power efficiency; and an 874-GHz radiometer suitable for airborne observation with state-of-the-art sensitivity at room temperature and less than 5 W of total power consumption.
In this paper, the design of a beacon transmitter that will be flown as a hosted payload on a geostationary satellite to enable propagation experiments at Q-band (37 to 41 GHz) frequencies is presented. The beacon uses a phased locked loop stabilized dielectric resonator oscillator and a solid-state power amplifier to achieve the desired output power. The satellite beacon antenna is configured as an offset-fed cutparaboloidal reflector.
In this paper, the design of a beacon transmitter that will be flown as a hosted payload on a geostationary satellite to enable propagation experiments at Q-band (37-41 GHz) frequencies is presented. The beacon uses a phased locked loop stabilized dielectric resonator oscillator and a solid-state power amplifier to achieve the desired output power. The satellite beacon antenna is configured as an offset-fed cut-paraboloidal reflector.
NISAR (NASA ISRO SAR, National Aeronautics and Space Administration, Indian Space Research Organization, Synthetic Aperture Radar) is an Earth science project currently in its final development phases at NASA Jet Propulsion Laboratory (JPL) and at ISRO. Due for launch in 2023 it will assess how our planet changes over time by measuring differences in the Earth’s solid surface due to factors like climate change, movement and melting of glaciers, earthquakes, land-slides, deforestation, agriculture and others. The enabling instrument for this mission is a dual band radar (L-Band and S-Band) that feeds a 12m deployable mesh reflector. Given the extreme accuracy needed to perform these measurements from Low Earth Orbit (LEO) some of the most stringent requirements were pushed onto the antenna subsystem to control phase and gain stability over time. In this paper we describe how environmental requirements affected the antenna design and what techniques were used to meet these requirements.
Thin films of perovskite ruthenates of the general formula ARuO 3 (A = Ca and Sr) are versatile electrical conductors for viable oxide electronics. They are also scientifically intriguing, as they exhibit nontrivial electromagnetic ground states depending on the A-site element. Among them, realization of the cubic perovskite (3C) BaRuO 3 in thin film form has been a challenge so far, because the 3C phase is metastable with the largest formation energy among the various polymorph phases of BaRuO 3 . In this study, 3C BaRuO 3 thin films are successfully prepared employing epitaxial stabilization. Here the 3C BaRuO 3 thin films show itinerant ferromagnetism with a transition temperature of ≈48 K and a non-Fermi liquid phase. The epitaxial stabilization of the 3C BaRuO 3 further enables to make a standard comparison of perovskite ruthenates, thereby establishing the importance of the Ru-O orbital hybridization in understanding the itinerant magnetic system.