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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 1,783 records · Page 99
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

An adaptive observer for single-input single-output linear systems.

A full order adaptive observer is described for observing the state of a single-input single-output observable continuous differential system with unknown parameters. Convergence of the observer states to those of the system is accomplished by directly changing the parameters of the observer using an adaptive law based upon Lyapunov stability theory. Observer eigenvalues may be freely chosen. Some restriction is placed upon the system input in that it must be sufficiently rich in frequencies in order to insure convergence.

Carroll, R. L.↗
NASA NTRS1973

The Kalman-Yacubovich lemma in adaptive control system design.

New results are presented that pertain to the design of model-reference adaptive control systems with the aid of the Kalman-Yacubovich lemma derived in connection with the problem of Lure. It is shown that the Kalman-Yacubovich lemma is a much more powerful tool for designing model-reference adaptive control systems than was previously thought.

Monopoli, R. V.↗
NASA NTRS1973

Adaptive ground implemented phased array

Tests were conducted to determine the feasibility of using an adaptive ground implemented phased array (AGIPA) to overcome the limitations of the radio frequency interference limited low data Tracking and Data Relay Satellite VHF return link. A feasibility demonstration model of a single user channel AFIPA system was designed, developed, fabricated, and evaluated. By scaling the frequency and aperture geometry from VHF to S-band, the system performance was more easily demonstrated in the controlled environment of an anechoic chamber. The testing procedure employs an AGIPA in which received signals from each element of the array are processed on the ground to form an adaptive, independent, computer controlled beam for each user.

Smith, J. M.↗
NASA NTRS1974

Conical isogrid adapter structural test results

The structural characteristics of isogrid composite structures are discussed. To demonstrate the feasibility of applying isogrid to conical structures, a full scale flanged isogrid conical adapter similar to the configuration of the D-1 Centaur equipment module was constructed. The adapter was tested to evaluate the response of the conical isogrid structure to various combinations of bending and axial compression loading. The analysis techniques for predicting conical isogrid structural capability are examined.

Dyer, J. E.↗
NASA NTRS1974

Optimal design of an unsupervised adaptive classifier with unknown priors

An adaptive detection scheme for M hypotheses was analyzed. It was assumed that the probability density function under each hypothesis was known, and that the prior probabilities of the M hypotheses were unknown and sequentially estimated. Each observation vector was classified using the current estimate of the prior probabilities. Using a set of nonlinear transformations, and applying stochastic approximation theory, an optimally converging adaptive detection and estimation scheme was designed. The optimality of the scheme lies in the fact that convergence to the true prior probabilities is ensured, and that the asymptotic error variance is minimum, for the class of nonlinear transformations considered. An expression for the asymptotic mean square error variance of the scheme was also obtained.

Kazakos, D.↗
NASA NTRS1974

Conical isogrid adapter structural test results. Appendix C: Cylindrical isogrid structures

Analysis techniques and data for evaluating the load carrying capabilities of cylindrical isogrid structures subjected to compression and body bending loads are presented. Structural tests were conducted on a 120-inch diameter by 37-inch long cylindrical adapter. Photographs and drawings of the flanged isogrid adapter structure are included. The subjects considered are: (1) summary of the test data resulting from structural analysis, (2) techniques for predicting local and general instability, (3) a method for predicting extended local instability, (4) the effects of basic parameter and constant variations in extended local stability analysis, and (5) evaluation of effective skin width and compression buckling of skin panels on the basis of test data.

Source record↗
NASA NTRS1973

Adaptive on-line classification of multi-spectral scanner data

A possible solution to the analysis of the massive amounts of multi-spectral scanner data from the Earth Resource Technical Satellite (ERTS) program is proposed. This solution is offered as an adaptive on-line classification scheme. The classifier is described as well as its controller which is based on ground truth data. Cluster analysis is presented as an alternative approach to the ground truth data. Adaptive feature selection is discussed and possible mini-computer implementations are offered.

Fromm, F. R.↗
NASA NTRS1974

A synthesis theory for the externally excited adaptive system /EEAS/

The externally excited adaptive system (EEAS) is a two-degree-of-freedom feedback system with a nonlinearity which is saturated hard by an external periodic signal. Under certain conditions, the EEAS responds quasi-linearly to command and plant disturbance signals, permitting the development of a quantitative synthesis theory for satisfying system tolerances despite large plant uncertainty. The great advantage of the EEAS is its zero sensitivity to plant gain variations, a property it shares with the self-oscillating adaptive system (SOAS). The EEAS is, however, more flexible than the SOAS in satisfying the quasi-linearity constraints. The essential difference is that in the EEAS the loop transmission bandwidth is not rigorously tied to the 'carrier' signal, as it is in the SOAS. There is a class of problems for which the EEAS is superior to the purely linear system, which in turn is superior to the SOAS. The superiority of the EEAS over the SOAS is especially marked in the case of significant plant disturbances, which generally vitiate a SOAS design.

Horowitz, I. M.↗
NASA NTRS1974

Adaptive compensation for an optical tracking telescope

The application of model referenced adaptive control theory to an optical tracking telescope is discussed. The capability of the adaptive technique to compensate for mount irregularities such as inertial variations and bearing friction is demonstrated via field test results on a large tracking telescope. Results are presented which show a 6 to 1 improvement in tracking accuracy for a worst-case satellite trajectory.

Gilbart, J. W.↗
NASA NTRS1974

Digital adaptive model following flight control

Simple mechanical linkages are often unable to cope with the many control problems associated with high performance aircraft maneuvering over a wide flight envelope. One procedure for retaining uniform handling qualities over such an envelope is to implement a digital adaptive controller. Towards such an implementation an explicit adaptive controller, which makes direct use of online parameter identification, has been developed and applied to the linearized equations of motion for a typical fighter aircraft. The system is composed of an online weighted least squares identifier, a Kalman state filter, and a single stage real model following control law. The corresponding control gains are readily adjustable in accordance with parameter changes to ensure asymptotic stability if the conditions for perfect model following are satisfied and stability in the sense of boundedness otherwise.

Alag, G. S.↗
NASA NTRS1972

An Adaptive Technique for a Redundant-Sensor Navigation System

An on-line adaptive technique is developed to provide a self-contained redundant-sensor navigation system with a capability to utilize its full potentiality in reliability and performance. The gyro navigation system is modeled as a Gauss-Markov process, with degradation modes defined as changes in characteristics specified by parameters associated with the model. The adaptive system is formulated as a multistage stochastic process: (1) a detection system, (2) an identification system and (3) a compensation system. It is shown that the sufficient statistics for the partially observable process in the detection and identification system is the posterior measure of the state of degradation, conditioned on the measurement history.

Chien, T. T.↗
NASA NTRS1975

Experimental and simulation study results of an Adaptive Video Guidance System /AVGS/

Studies relating to stellar-body exploration programs have pointed out the need for an adaptive guidance scheme capable of providing automatic real-time guidance and site selection capability. For the case of a planetary lander, without such guidance, targeting is limited to what are believed to be generally benign areas in order to ensure a reasonable landing-success probability. Typically, the Mars Viking Lander will be jeopardized by obstacles exceeding 22 centimers in diameter. The benefits of on-board navigation and real-time selection of a landing site and obstacle avoidance have been demonstrated by the Apollo lunar landings, in which man performed the surface sensing and steering functions. Therefore, an Adaptive Video Guidance System (AVGS) has been developed, bread-boarded, and flown on a six-degree-of-freedom simulator.

Schappell, R. T.↗
NASA NTRS1975

J-Adaptive estimation with estimated noise statistics

The J-Adaptive estimator described by Jazwinski and Hipkins (1972) is extended to include the simultaneous estimation of the statistics of the unmodeled system accelerations. With the aid of simulations it is demonstrated that the J-Adaptive estimator with estimated noise statistics can automatically estimate satellite orbits to an accuracy comparable with the data noise levels, when excellent, continuous tracking coverage is available. Such tracking coverage will be available from satellite-to-satellite tracking.

Jazwinski, A. H.↗
NASA NTRS1976

Research in digital adaptive flight controllers

A design study of adaptive control logic suitable for implementation in modern airborne digital flight computers was conducted. Both explicit controllers which directly utilize parameter identification and implicit controllers which do not require identification were considered. Extensive analytical and simulation efforts resulted in the recommendation of two explicit digital adaptive flight controllers. Interface weighted least squares estimation procedures with control logic were developed using either optimal regulator theory or with control logic based upon single stage performance indices.

Kaufman, H.↗
NASA NTRS1975

Atmosphere explorer /AE-C/ adaptive mission design and trajectory performance

The preflight mission design and in-flight execution are presented to illustrate the actual utilization of the adaptive nature of this mission. Spacecraft systems (propulsion, attitude, accelerometer) and software (maneuver program) features which contribute to the adaptive trajectory flexibility are discussed. Descriptions of procedures used to handle low perigee maneuver operations (to 130 km), for achieving ground track control and orbit phasing, for making a transition from elliptical to circular orbits, and for circular orbit restoration and maintenance are presented in detail. The 85 maneuvers made during the first 17 months of the mission are summarized.

Barbieri, R. W.↗
NASA NTRS1975

Parameter adaptive control of multivariable systems

Model reference adaptive controllers for multivariable plants are designed using only input and output signals rather than the complete state vector. The design is based on Liapunov's direct method, and the Meyer-Kalman-Yacubovich lemma. State variable filters are employed to avoid differentiating output signals. Augmented error signals are used in deriving stable adaptive control laws which assure that the normally used response error signals approach zero asymptotically.

Monopoli, R. V.↗
NASA NTRS1975

Adaptation of an existing cosmic ray ionization spectrometer experiment to Spacelab

This paper examines the technique of adapting an existing experiment to a Shuttle sortie mission. A sample cosmic-ray balloon experiment was studied to determine the feasibility of this cost-saving technique, which is applicable to a large spectrum of existing experiments, and to determine the programmatic impact and key problems. The main areas investigated include the determination of required modifications, steps in integration to the Spacelab/Shuttle, and the impact on orbital support and operations. One of the main problems in equipment adaptation is the acoustical loading during Shuttle boost; an environmental cover design presented herein shows a potential method to attain the required acoustic attenuation.

Alvarado, U. R.↗