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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 703 records · Page 39
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NASA NTRS2011

Polarization Compensation of Fresnel Aberrations in Telescopes

Large aperture space telescopes are built with low F# s to accommodate the mechanical constraints of launch vehicles and to reduce resonance frequencies of the on-orbit system. Inherent with these low F# s is Fresnel polarization which affects image quality. We present the design and modeling of a nano-structure consisting of birefringent layers to control polarization and increase contrast. Analysis shows a device that functions across a 400nm bandwidth tunable from 300nm to 1200nm. This Fresnel compensator device has a cross leakage of less than 0.001 retardance.

Clark, Natalie↗
NASA NTRS2011

A Control Allocation System for Automatic Detection and Compensation of Phase Shift Due to Actuator Rate Limiting

This paper proposes a control allocation system that can detect and compensate the phase shift between the desired and the actual total control effort due to rate limiting of the actuators. Phase shifting is an important problem in control system applications since it effectively introduces a time delay which may destabilize the closed loop dynamics. A relevant example comes from flight control where aggressive pilot commands, high gain of the flight control system or some anomaly in the system may cause actuator rate limiting and effective time delay introduction. This time delay can instigate Pilot Induced Oscillations (PIO), which is an abnormal coupling between the pilot and the aircraft resulting in unintentional and undesired oscillations. The proposed control allocation system reduces the effective time delay by first detecting the phase shift and then minimizing it using constrained optimization techniques. Flight control simulation results for an unstable aircraft with inertial cross coupling are reported, which demonstrate phase shift minimization and recovery from a PIO event.

Yildiz, Yidiray↗
NASA NTRS2004

EHW Approach to Temperature Compensation of Electronics

Efforts are under way to apply the concept of evolvable hardware (EHW) to compensate for variations, with temperature, in the operational characteristics of electronic circuits. To maintain the required functionality of a given circuit at a temperature above or below the nominal operating temperature for which the circuit was originally designed, a new circuit would be evolved; moreover, to obtain the required functionality over a very wide temperature range, there would be evolved a number of circuits, each of which would satisfy the performance requirements over a small part of the total temperature range. The basic concepts and some specific implementations of EHW were described in a number of previous NASA Tech Briefs articles, namely, "Reconfigurable Arrays of Transistors for Evolvable Hardware" (NPO-20078), Vol. 25, No. 2 (February 2001), page 36; Evolutionary Automated Synthesis of Electronic Circuits (NPO- 20535), Vol. 26, No. 7 (July 2002), page 37; "Designing Reconfigurable Antennas Through Hardware Evolution" (NPO-20666), Vol. 26, No. 7 (July 2002), page 38; "Morphing in Evolutionary Synthesis of Electronic Circuits" (NPO-20837), Vol. 26, No. 8 (August 2002), page 31; "Mixtrinsic Evolutionary Synthesis of Electronic Circuits" (NPO-20773) Vol. 26, No. 8 (August 2002), page 32; and "Synthesis of Fuzzy-Logic Circuits in Evolvable Hardware" (NPO-21095) Vol. 26, No. 11 (November 2002), page 38. To recapitulate from the cited prior articles: EHW is characterized as evolutionary in a quasi-genetic sense. The essence of EHW is to construct and test a sequence of populations of circuits that function as incrementally better solutions of a given design problem through the selective, repetitive connection and/or disconnection of capacitors, transistors, amplifiers, inverters, and/or other circuit building blocks. The connection and disconnection can be effected by use of field-programmable transistor arrays (FPTAs). The evolution is guided by a search-andoptimization algorithm (in particular, a genetic algorithm) that operates in the space of possible circuits to find a circuit that exhibits an acceptably close approximation of the desired functionality. The evolved circuits can be tested by mathematical modeling (that is, computational simulation) only, tested in real hardware, or tested in combinations of computational simulation and real hardware.

Stoica, Adrian↗
NASA NTRS2004

Compensating for Effects of Humidity on Electronic Noses

A method of compensating for the effects of humidity on the readouts of electronic noses has been devised and tested. The method is especially appropriate for use in environments in which humidity is not or cannot be controlled for example, in the vicinity of a chemical spill, which can be accompanied by large local changes in humidity. Heretofore, it has been common practice to treat water vapor as merely another analyte, the concentration of which is determined, along with that of the other analytes, in a computational process based on deconvolution. This practice works well, but leaves room for improvement: changes in humidity can give rise to large changes in electronic-nose responses. If corrections for humidity are not made, the large humidity-induced responses may swamp smaller responses associated with low concentrations of analytes. The present method offers an improvement. The underlying concept is simple: One augments an electronic nose with a separate humidity and a separate temperature sensor. The outputs of the humidity and temperature sensors are used to generate values that are subtracted from the readings of the other sensors in an electronic nose to correct for the temperature-dependent contributions of humidity to those readings. Hence, in principle, what remains after corrections are the contributions of the analytes only. Laboratory experiments on a first-generation electronic nose have shown that this method is effective and improves the success rate of identification of analyte/ water mixtures. Work on a second-generation device was in progress at the time of reporting the information for this article.

Homer, Margie↗
NASA NTRS2012

Thermal expansion compensator having an elastic conductive element bonded to two facing surfaces

A thermal expansion compensator is provided and includes a first electrode structure having a first surface, a second electrode structure having a second surface facing the first surface and an elastic element bonded to the first and second surfaces and including a conductive element by which the first and second electrode structures electrically and/or thermally communicate, the conductive element having a length that is not substantially longer than a distance between the first and second surfaces.

Determan, William↗
NASA NTRS2012

Phase Change Material for Temperature Control of Loop Heat Pipe Compensation Chamber

The compensation chamber (CC) of a loop heat pipe (LHP) requires a stable temperature. In the current technology, the CC is commonly cold biased by exposing it to deep space, and active heater control is used to maintain its temperature stable. Heater power required for a typical LHP with a 300 W heat transport capacity is as much as 25 W. If multiple LHPs are used, heater power requirement could be a bigger issue. Also heater controller or temperature sensor failure could lead to a LHP or mission failure. This paper presents an innovative concept of using phase change material (PCM) for temperature control of LHP CC. Some of the electronics and/or detector assembly waste heat is stored in the PCM and transferred to the LHP CC by constant conductance heat pipes (CCHPs). Phase change of the PCM occurs at a constant temperature and maintains the LHP CC temperature stable. It eliminates heater power and active heater control for the CC. It also increases the reliability of LHP.

Choi, Michael K.↗
NASA NTRS2012

Method of assembling a thermal expansion compensator

A thermal expansion compensator is provided and includes a first electrode structure having a first surface, a second electrode structure having a second surface facing the first surface and an elastic element bonded to the first and second surfaces and including a conductive element by which the first and second electrode structures electrically and/or thermally communicate, the conductive element having a length that is not substantially longer than a distance between the first and second surfaces.

Determan, William↗
NASA NTRS2012

An Intelligent Strain Gauge with Debond Detection and Temperature Compensation

The harsh rocket propulsion test environment will expose any inadequacies associated with preexisting instrumentation technologies, and the criticality for collecting reliable test data justifies investigating any encountered data anomalies. Novel concepts for improved systems are often conceived during the high scrutiny investigations by individuals with an in-depth knowledge from maintaining critical test operations. The Intelligent Strain Gauge concept was conceived while performing these kinds of activities. However, the novel concepts are often unexplored even if it has the potential for advancing the current state of the art. Maturing these kinds of concepts is often considered to be a tangential development or a research project which are both normally abandoned within the propulsion-oriented environment. It is also difficult to justify these kinds of projects as a facility enhancement because facility developments are only accepted for mature and proven technologies. Fortunately, the CIF program has provided an avenue for bringing the Intelligent Strain Gauge to fruition. Two types of fully functional smart strain gauges capable of performing reliable and sensitive debond detection have been successfully produced. Ordinary gauges are designed to provide test article data and they lack the ability to supply information concerning the gauge itself. A gauge is considered to be a smart gauge when it provides supplementary data relating other relevant attributes for performing diagnostic function or producing enhanced data. The developed strain gauges provide supplementary signals by measuring strain and temperature through embedded Karma and nickel chromium (NiCr) alloy elements. Intelligently interpreting the supplementary data into valuable information can be performed manually, however, integrating this functionality into an automatic system is considered to be an intelligent gauge. This was achieved while maintaining a very low mass. The low mass enables debond detection and temperature compensation to be performed when the gauge is utilized on small test articles. It was also found that the element's mass must be relatively small to avoid overbearing the desired thermal dissipation characteristics. Detecting the degradation of a gauge s bond was reliably achieved by correlating thermal dissipation with the bond s integrity. This was accomplished by precisely coupling a NiCr element with a Karma element for accurately interjecting and quantifying thermal energy. A finite amount of thermal energy is consistently placed in the gauge by electrically powering the NiCr element. The energy will only be temporarily stored before it begins to dissipate into the surrounding structure through the gauge bond. The ability to transmit the energy into the structure becomes greatly inhibited by any discontinuity in the bond s substrate. Therefore, the way the thermal dissipation occurs will reveal even the slightest change in the integrity of the bond.

Jensen, Scott L.↗
NASA NTRS2012

2011-2012 Dryden Center Innovation Fund End of the Year Report: Altitude-Compensating Rocket Nozzles

This report highlights one of the many successful projects at the NASA Dryden Flight Research Center that was approved for FY12 funding under the Center Innovation Fund. This project was focused on advancing the technology readiness level of one specific type of altitude-compensating nozzle: the dual-bell rocket nozzle. When considering a rocket's performance over its entire integrated trajectory, the dual-bell nozzle has been predicted to achieve a higher total impulse over the conventional bell nozzle, which is expected to result in a greater capability of payload mass to low-Earth orbit. Although the dual-bell rocket nozzle has been thoroughly studied for several decades, this nozzle has still not been adequately tested in a relevant flight-like environment. This report provides highlights and top-level details on the FY12 feasibility effort to advance this promising technology through flight test, a collaborative effort which leverages NASA Marshall's dual-bell nozzle research and development with Dryden's expertise in propulsion-focused flight testing. To accomplish this goal, the NASA F-15B is proposed as the testbed for the initial flight-test campaign to advance this greatly needed capability.

Jones, Daniel S.↗
NASA NTRS2015

Altitude Compensating Nozzle

The dual-bell nozzle (fig. 1) is an altitude-compensating nozzle that has an inner contour consisting of two overlapped bells. At low altitudes, the dual-bell nozzle operates in mode 1, only utilizing the smaller, first bell of the nozzle. In mode 1, the nozzle flow separates from the wall at the inflection point between the two bell contours. As the vehicle reaches higher altitudes, the dual-bell nozzle flow transitions to mode 2, to flow full into the second, larger bell. This dual-mode operation allows near optimal expansion at two altitudes, enabling a higher mission average specific impulse (Isp) relative to that of a conventional, single-bell nozzle. Dual-bell nozzles have been studied analytically and subscale nozzle tests have been completed.1 This higher mission averaged Isp can provide up to a 5% increase2 in payload to orbit for existing launch vehicles. The next important step for the dual-bell nozzle is to confirm its potential in a relevant flight environment. Toward this end, NASA Marshall Space Flight Center (MSFC) and Armstrong Flight Research Center (AFRC) have been working to develop a subscale, hot-fire, dual-bell nozzle test article for flight testing on AFRC's F15-D flight test bed (figs. 2 and 3). Flight test data demonstrating a dual-bell ability to control the mode transition and result in a sufficient increase in a rocket's mission averaged Isp should help convince the launch service providers that the dual-bell nozzle would provide a return on the required investment to bring a dual-bell into flight operation. The Game Changing Department provided 0.2 FTE to ER42 for this effort in 2014.

Ruf, Joseph H.↗
NASA NTRS2020

Progress of Coating Stress Compensation of Silicon Mirrors for Lynx X-ray Telescope Mission Concept Using Thermal Oxide Patterning Method

A thermal oxide patterning method has proven to be effective for correcting coating-stress-induced distortion on flat silicon wafers. We report progress on developing this method for correcting curved silicon mirrors distorted by front-side iridium coatings. Owing to the difference in geometry, a finite element model has been established to calculate the appropriate duty cycle maps in thermal oxide hexagon patterns used for compensation. In addition, a photolithographic process, along with three-dimensional printed equipment, has been developed for creating patterns precisely on the back side of curved mirrors. The developed method has been used to recover the original surface shape of two silicon mirrors which are 100-mm long, 0.5-mm thick, having 312-mm radius of curvature, and 30 deg in azimuthal span (Wolter-I geometry). These mirrors’ front sides are sputter-coated by 20-nm iridium layers with ∼-70 N∕m integrated stress. Measurement results show that the developed method can mitigate coating-induced distortion by a factor of ∼5 in RMS height and ∼4 in RMS slope error, corresponding to ∼0.5 arc sec RMS slope error. Residual errors after correction are dominated by midfrequency ripples created during the annealing process, which will be resolved in the future. The presented method is precise and inexpensive and a potential candidate for resolving the coating stress issue for Lynx optics in the future.

x-ray↗
NASA NTRS2002

Dispersion compensation in whispering gallery modes

We show that manipulation by a spatial profile of refractive index of a circularly symmetric dielectric cavity results in a novel way of fine tuning frequency separations as well as spatial localizations of high-Q whispering gallery modes excited in the cavity. The method enables dispersion compensation in the modes (spectrum equalization), diminishes the quality-factor limitation by surface roughness and contamination, and enables critical coupling to ultra-high-Q modes without maintaining an air-gap with evanescent couplers.

photonic↗
NASA NTRS1996

Characterization and Compensation of the Atmosphere for the Inversion of AVIRIS Calibrated Radiance to Apparent Surface Reflectance

Calibrated radiance spectra measured remotely, record the integrated effects of the solar source, the atmosphere, and the surface. To pursue scientific research and applications, based on the molecular absorptions and constituent scattering properties of the surface, the solar source and atmosphere must be characterized and compensated in the spectra. This paper describes a set of radiative transfer spectral fitting algorithms to characterize the absorbing and scattering constituents of the atmosphere from calibrated AVIRIS spectra.

atmosphere↗
NASA NTRS1993

Probe Compensation in Cylindrical Near-Field Scanning: A Novel Simulation Methodology

Probe pattern compensation is essential in near-field scanning geometry, where there is a greatneed to accurately know far-field pattern at wide angular range. This paper focuses on a novelformulation and computer simulation to determine the precise need for and effect of probecompensation in cylindrical near-field scanning. The methodology is applied to a linear test arrayantenna and the NASA scatterometer radar antenna. The formulation is based on representing theprobe (circular aperture) by its equivalent tangential magnetic currents. The interaction between theprobe equivalent aperture currents and the test antenna fields is obtained with the application ofreciprocity theorem. This allows us to obtain the probe vector output pickup integral which isproportional to the amplitude and phase of the electric field induced in the probe aperture with respectto its position to the test antenna.

Rahmat-Samii, Y↗
NASA NTRS2020

Investigation Of Prandtl-Ishlinskii Hysteresis Compensation for Deep Space Optical Communications Pointing Control

This paper studies the simulated performance of the Deep Space Optical Communication (DSOC) laser downlink pointing control system that has a pointing requirement at the sub-microradian scale. To achieve the required pointing precision, the DSOC Flight Laser Transceiver (FLT) point-ahead mirror (PAM) employs piezoelectric actuators, which are widely used in precision applications due to their high motion resolution, rapid response, and high output forces. However, a piezoelectric actuator's performance is often limited by nonlinearities in their response, most significantly hysteresis. To study the effect of hysteresis on our simulated pointing performance, an invertible hysteresis model is developed using the Classical Prantdl-Ishlinskii (CPI) method. The simulation includes models of DSOC hardware and electronic system components based on key parameters (bias, frequency response, noise), with the hysteresis modeled in the PAM piezo actuator dynamics. A Proportional-Integral controller provides feedback with measurements from two potential sources: strain gauge sensors or a photon-counting camera. To compensate for hysteresis behavior, a feedforward inverse CPI hysteresis model is implemented in the control system. Two CPI models are built using different sampling methods (uniform sampling and cosine spacing) and controller performance is compared. For the maximum command range of ±400 μrad at 1 mHz, results show that the feedforward combined with feedback control reduces output tracking error by 50% or 58% (to 0.20 or 0.38 μrad) compared to feedback control alone (from 0.40 or 0.90 μrad), corresponding to the uniform-sampled and cosine-sampled CPI models, respectively.

Marinello, Lindsey A.↗