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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 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Actuated Hybrid Mirror Telescope

The figure depicts the planned Actuated Hybrid Mirror Telescope (AHMT), which is intended to demonstrate a new approach to the design and construction of wide-aperture spaceborne telescopes for astronomy and Earth science. This technology is also appropriate for Earth-based telescopes. The new approach can be broadly summarized as using advanced lightweight mirrors that can be manufactured rapidly at relatively low cost. More specifically, it is planned to use precise replicated metallic nanolaminate mirrors to obtain the required high-quality optical finishes. Lightweight, dimensionally stable silicon carbide (SiC) structures will support the nanolaminate mirrors in the required surface figures. To enable diffraction- limited telescope performance, errors in surface figures will be corrected by use of mirror-shape-control actuators that will be energized, as needed, by a wave-front-sensing and control system. The concepts of nanolaminate materials and mirrors made from nanolaminate materials were discussed in several previous NASA Tech Briefs articles. Nanolaminates constitute a relatively new class of materials that can approach theoretical limits of stiffness and strength. Nanolaminate mirrors are synthesized by magnetron sputter deposition of metallic alloys and/or compounds on optically precise master surfaces to obtain optical-quality reflector surfaces backed by thin shell structures. As an integral part of the deposition process, a layer of gold that will constitute the reflective surface layer is deposited first, eliminating the need for a subsequent and separate reflective-coating process. The crystallographic textures of the nanolaminate will be controlled to optimize the performance of the mirror. The entire deposition process for making a nanolaminate mirror takes less than 100 hours, regardless of the mirror diameter. Each nanolaminate mirror will be bonded to its lightweight SiC supporting structure. The lightweight nanolaminate mirrors and SiC supporting structures will be fabricated from reusable master molds. The mirror-shape-control actuators will be low-power, high-capacitance lead magnesium niobate electrostrictive actuators that will be embedded in the SiC structures. The mode of operation of these actuators will be such that once power was applied, they will change in length and once power was removed, they will maintain dimensional stability to nanometer precision. This mode of operation will enable the use of low-power, minimally complex electronic control circuitry. The wave-front-sensing and control system will be designed and built according to a two-stage architecture. The first stage will be implemented by a Shack- Hartmann (SH) sensor subsystem, which will provide a large capture range. The second, higher-performance stage will be implemented by an image-based wave-front-sensing subsystem that will include a phase-retrieval camera (PRC), and will utilize phase retrieval and other techniques to measure wavefront error directly. Phase retrieval is a process in which multiple images of an unresolved object are iterated to estimate the phase of the optical system that acquired the images. The combination of SH and phase-retrieval sensors will afford the virtues of both a dynamic range of 105 and an accuracy of <10 nm.

Hickey, Gregory↗
NASA NTRS1979

Comparison between thermochemical and phase stability data for the quartz-coesite-stishovite transformations

Phase stability and elasticity data have been used to calculate the Gibbs free energy, enthalpy, and entropy changes at 298 K and 1 bar associated with the quartz-coesite and coesite-stishovite transformations in the system SiO2. For the quartz-coesite transformation, these changes disagree by a factor of two or three with those obtained by calorimetric techniques. The phase boundary for this transformation appears to be well determined by experiment; the discrepancy, therefore, suggests that the calorimetric data for coesite are in error. Although the calorimetric and phase stability data for the coesite-stishovite transformation yield the same transition pressure at 298 K, the phase-boundary slopes disagree by a factor of two. At present, it is not possible to determine which of the data are in error. Thus serious inconsistencies exist in the thermodynamic data for the polymorphic transformations of silica.

Weaver, J. S.↗
DOE OSTI2024

Predicting ptychography probe positions using single-shot phase retrieval neural network

Ptychography is a powerful imaging technique that is used in a variety of fields, including materials science, biology, and nanotechnology. However, the accuracy of the reconstructed ptychography image is highly dependent on the accuracy of the recorded probe positions which often contain errors. These errors are typically corrected jointly with phase retrieval through numerical optimization approaches. When the error accumulates along the scan path or when the error magnitude is large, these approaches may not converge with satisfactory result. We propose a fundamentally new approach for ptychography probe position prediction for data with large position errors, where a neural network is used to make single-shot phase retrieval on individual diffraction patterns, yielding the object image at each scan point. The pairwise offsets among these images are then found using a robust image registration method, and the results are combined to yield the complete scan path by constructing and solving a linear equation. We show that our method can achieve good position prediction accuracy for data with large and accumulating errors on the order of 10 2 pixels, a magnitude that often makes optimization-based algorithms fail to converge. For ptychography instruments without sophisticated position control equipment such as interferometers, our method is of significant practical potential.

47 OTHER INSTRUMENTATION↗
NASA NTRS1975

Digital second-order phase-locked loop

Actual tests with second-order digital phase-locked loop at simulated relative Doppler shift of 1x0.0001 produced phase lock with timing error of 6.5 deg and no appreciable Doppler bias. Loop thus appears to achieve subcarrier synchronization and to remove bias due to Doppler shift in range of interest.

Holmes, J. K.↗
NASA NTRS1977

Precision measurement of changes in physical dimensions

Interferometric method is used to measure small changes in size of optical materials. Error introduced with optical phase shifts occurring with time is overcome by using parts of Fabry-Perot resonators with unequal lengths. Both stability of optical phase shifts upon reflection from multilayer stacks and dimensional stability of optical contacts is measured.

Berthold, J. W., III↗
NASA NTRS1976

Nonintrusive Flowmeter

The results of analytical and experimental work performed in the design, fabrication, and test of a prototype nonintrusive gaging system for use in monitoring the consumption of earth-storable fuels and oxidants in either a one-g or a zero-g environment are explained. The design specifications were those applicable to the reaction control system and to the orbital maneuvering system (OMS) fuel and oxidant on the space shuttle while in orbit. The major requirement was for the measurement of flow pulses with sufficient accuracy to provide a continuous knowledge of the fuel and oxidant remaining in the OMS system to within 1% or better. An ultrasonic frequency chirp technique was used having a high inherent rejection for signals traversing stray paths, and for random noise generated by the flowing liquid. A detailed analysis of the frequency chirp approach for two modes of operation (period and phase changes), including an error analysis are reported.

Greene, M. W.↗
NASA NTRS1978

An Evaluation of optional timing/synchronization features to support selection of an optimum design for the DCS digital communication network

The task was to evaluate the ability of a set of timing/synchronization subsystem features to provide a set of desirable characteristics for the evolving Defense Communications System digital communications network. The set of features related to the approaches by which timing/synchronization information could be disseminated throughout the network and the manner in which this information could be utilized to provide a synchronized network. These features, which could be utilized in a large number of different combinations, included mutual control, directed control, double ended reference links, independence of clock error measurement and correction, phase reference combining, and self organizing.

Bradley, D. B.↗
NASA NTRS1978

Effect of various features on the life cycle cost of the timing/synchronization subsystem of the DCS digital communications network

The effect on the life cycle cost of the timing subsystem was examined, when these optional features were included in various combinations. The features included mutual control, directed control, double-ended reference links, independence of clock error measurement and correction, phase reference combining, self-organization, smoothing for link and nodal dropouts, unequal reference weightings, and a master in a mutual control network. An overall design of a microprocessor-based timing subsystem was formulated. The microprocessor (8080) implements the digital filter portion of a digital phase locked loop, as well as other control functions such as organization of the network through communication with processors at neighboring nodes.

Kimsey, D. B.↗
NASA NTRS1980

Estimation of Kalman filter model parameters from an ensemble of tests

A methodology for estimating initial mean and covariance parameters in a Kalman filter model from an ensemble of nonidentical tests is presented. In addition, the problem of estimating time constants and process noise levels is addressed. Practical problems such as developing and validating inertial instrument error models from laboratory test data or developing error models of individual phases of a test are generally considered.

Gibbs, B. P.↗
NASA NTRS1980

System performance conclusions

The advantages and disadvantages of reducing power levels and using antennas with diameters smaller than 1 Km were evaluated if rectenna costs and land usage requirements become major factors, operating at 5800 megahertz should be considered. Three sequences (random, incoherent phasing, and concentric rings - center to edge) provided satisfactory performance in that the resultant sidelobe levels during startup/ shutdown were lower than the steady-state levels present during normal operations. Grating lobe peaks and scattered power levels were used to determine the array/subarray mechanical alignment requirements. The antenna alignment requirement is 1 min or 3 min depending on phase control configuration. System error parameters were defined to minimize scattered microwave power.

Arndt, G. D.↗
NASA NTRS1988

Angular navigation capabilities of short baseline phase delay interferometry

Short baseline phase delay interferometry can provide angular navigation capabilities which are competitive with current accuracies for group delay Very Long Baseline Interferometry (VLBI) on intercontinental baselines. In addition, a number of operational considerations make short baseline interferometry attractive, including enhanced mutual visibility, ability to observe at higher elevation angles, and the possibility of processing data in realtime. To make use of the higher precision phase delay datatype, however, the cycle ambiguity associated with the observed interferometric phase must be resolved. Results are presented for two experiments, on baselines of 5.9 and 253 km, for which RF phase connection appears to have been reliably achieved for several groups of angularly close radio sources. The dependence of the resulting phase delay residuals on elevation suggests that temporal fluctuations in the line-of-sight troposphere delay are a dominant error source. The observed RMS phase delay residuals of 10 psec or less suggest that baselines of order 100 km could provide high-efficiency angular navigation with accuracies well below 50 nrad. Plans for further work at the Goldstone Deep Space Communication Complex are reviewed.

Edwards, C. D.↗
NASA NTRS1989

Impact of tether cutting on onboard navigation during the Tethered Satellite Mission-1

The first Tethered Satellite System mission (TSS-1) is manifested for Shuttle Flight STS-44 in January of 1991. The TSS mission presents a new challenge to engineers, requiring advanced guidance, navigation and control concepts. Current NASA flight rules require that the navigational state of the Orbiter at deorbit burn be known to an accuracy of 20 nautical miles. Response of the Shuttle crew to this contingency may involve cutting the tether prior to a complete retrieval. The degradation of the navigational state accuracy as modelled by Shuttle navigation system is examined. Responses to the loss of communication scenario are proposed for two cases. The first case examines navigational performance during a nominal attitude profile. The second case is identical to the first, with the inclusion of modelled tether electrodynamical forces. Comparisons of trajectories propagated from the onboard navigational state vector and a reference ephemeris state vector were performed, with the tether cut simulated at various points during the mission. Additionally, updates to the onboard navigational state via ground uplinks were provided prior to the assumed loss of communication. Through these comparisons, the onboard navigation state error was determined. Alternative responses result from efforts to minimize this error during the various phases of TSS-1 deployment. These results demonstrated existing NASA flight rules could be violated by cutting the tether, and suggests reponses to a loss of communications contingency to maintain a more accurate navigational state.

Pirker, Dana M.↗
NASA NTRS1989

A forward error correction technique using a high-speed, high-rate single chip codec

The authors describe an error-correction coding approach that allows operation in either burst or continuous modes at data rates of multiple hundreds of megabits per second. Bandspreading is low since the code rate is 7/8 or greater, which is consistent with high-rate link operation. The encoder, along with a hard-decision decoder, fits on a single application-specific integrated circuit (ASIC) chip. Soft-decision decoding is possible utilizing applique hardware in conjunction with the hard-decision decoder. Expected coding gain is a function of the application and is approximately 2.5 dB for hard-decision decoding at 10-5 bit-error rate with phase-shift-keying modulation and additive Gaussian white noise interference. The principal use envisioned for this technique is to achieve a modest amount of coding gain on high-data-rate, bandwidth-constrained channels. Data rates of up to 300 Mb/s can be accommodated by the codec chip. The major objective is burst-mode communications, where code words are composed of 32 n data bits followed by 32 overhead bits.

Boyd, R. W.↗
NASA NTRS1990

Training effectiveness of an intelligent tutoring system for a propulsion console trainer

A formative evaluation was conducted on an Intelligent Tutoring System (ITS) developed for tasks performed on the Propulsion Console. The ITS, which was developed primarily as a research tool, provides training on use of the Manual Select Keyboard (MSK). Three subjects completed three phases of training using the ITS: declarative, speed, and automaticity training. Data were collected on several performance dimensions, including training time, number of trials performed in each training phase, and number of errors. Information was also collected regarding the user interface and content of training. Suggestions for refining the ITS are discussed. Further, future potential uses and limitations of the ITS are discussed. The results provide an initial demonstration of the effectiveness of the Propulsion Console ITS and indicate the potential benefits of this form of training tool for related tasks.

Johnson, Debra Steele↗
NASA NTRS1991

Ground support system methodology and architecture

A synergistic approach to systems test and support is explored. A building block architecture provides transportability of data, procedures, and knowledge. The synergistic approach also lowers cost and risk for life cycle of a program. The determination of design errors at the earliest phase reduces cost of vehicle ownership. Distributed scaleable architecture is based on industry standards maximizing transparency and maintainability. Autonomous control structure provides for distributed and segmented systems. Control of interfaces maximizes compatibility and reuse, reducing long term program cost. Intelligent data management architecture also reduces analysis time and cost (automation).

Schoen, P. D.↗
NASA NTRS1992

Investigation of Bandwidth-Efficient Coding and Modulation Techniques

The necessary technology was studied to improve the bandwidth efficiency of the space-to-ground communications network using the current capabilities of that network as a baseline. The study was aimed at making space payloads, for example the Hubble Space Telescope, more capable without the need to completely redesign the link. Particular emphasis was placed on the following concepts: (1) what the requirements are which are necessary to convert an existing standard 4-ary phase shift keying communications link to one that can support, as a minimum, 8-ary phase shift keying with error corrections applied; and (2) to determine the feasibility of using the existing equipment configurations with additional signal processing equipment to realize the higher order modulation and coding schemes.

Osborne, William P.↗
NASA NTRS1991

The development of an autonomous rendezvous and docking simulation using rapid integration and prototyping technology

A generic planar 3 degree of freedom simulation was developed that supports hardware in the loop simulations, guidance and control analysis, and can directly generate flight software. This simulation was developed in a small amount of time utilizing rapid prototyping techniques. The approach taken to develop this simulation tool, the benefits seen using this approach to development, and on-going efforts to improve and extend this capability are described. The simulation is composed of 3 major elements: (1) Docker dynamics model, (2) Dockee dynamics model, and (3) Docker Control System. The docker and dockee models are based on simple planar orbital dynamics equations using a spherical earth gravity model. The docker control system is based on a phase plane approach to error correction.

Shackelford, John H.↗
NASA NTRS1992

Digital implementation of vibration suppression controllers for LSS

A synthesis procedure for positivity controllers is described, and both simulation and experimental results for vibration suppression control experiments at the NASA Marshall ACES and the NASA Langley MiniMAST ground test facilities are presented. Positivity-designed controllers provide general stability robustness to modeling errors, coupled with controller phase compensation which provides stability margins required for actual implementation. A multivariable scaling method of positivity-designed controllers is used for the on-line tuning of nominal digital controllers. A phase compensation method uses model information to predict system measurements and controller states for compensating the nominal controllers for unmodeled time delays in the system.

Bosse, A.↗