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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Detection of Extraterrestrial Ecology (Exoecology)

Researchers in the Astrobiology Technology Branch at Ames Research Center have begun investigating alternate concepts for the detection of extraterrestrial life. We suggest searching for extraterrestrial ecology, exoecology, as well as for extraterrestrial biology, exobiology. Ecology describes the interactions of living things with their environment. All ecosystems are highly constrained by their environment and are constrained by well-known system design principles. Ecology could exist wherever there is an energy source and living I things have discovered some means to capture, store, and use the available energy. Terrestrial ecosystems use as energy sources, light, organic molecules, and in thermal vents and elsewhere, simple inorganic molecules. Ecosystem behavior is controlled by matter and energy conservation laws and can be described by linear and nonlinear dynamic systems theory. Typically in an ecosystem different molecules are not in chemical equilibrium and scarce material is conserved, stored, or recycled. Temporal cycles and spatial variations are often observed. These and other -eneral principles of exoecology can help guide the search for extraterrestrial life. The chemical structure observed in terrestrial biology may be highly contingent on evolutionary accidents. Oxygen was not always abundant on Earth. Primitive sulfur bacteria use hydrogen sulfide and sulfur to perform photosynthesis instead of water and oxygen. Astrobiologists have assumed, for the sake of narrowing and focusing our life detection strategies, that extraterrestrial life will have detailed chemical similarities with terrestrial life. Such assumptions appear very reasonable and they allow us to design specific and highly sensitive life detection experiments. But the fewer assumptions we make, the less chance we have of being entirely wrong The best strategy for the detection of extraterrestrial life could be a mixed strategy. We should use detailed assumptions based on terrestrial biology to guide some but not all future searches for alien life. The systems principles of exoecology seem much more fundamental and inescapable than the terrestrial biology analogies of exobiology. We should search for exoecology as well as exobiology.

Jones, Harry↗
NASA NTRS1974

Analysis of the feedback system in a nonintrusive dynamic flowmeter for measuring Pogo oscillations

Equations were developed which describe the closed loop feedback system operation of a proposed ultrasonic, dynamic, nonintrusive flowmeter whose design is based on a constant phase, voltage controlled frequency feedback concept. These equations are based on linear feedback system theory. The time constant of a low pass filter is taken into account. The equations show that the larger the open loop gain, the smaller the error due to fluctuations in the speed of sound and the smaller the effective time constant.

Chapin, W. G.↗
NASA NTRS1973

Introduction to computer image processing

Theoretical backgrounds and digital techniques for a class of image processing problems are presented. Image formation in the context of linear system theory, image evaluation, noise characteristics, mathematical operations on image and their implementation are discussed. Various techniques for image restoration and image enhancement are presented. Methods for object extraction and the problem of pictorial pattern recognition and classification are discussed.

Moik, J. G.↗
NASA NTRS1975

Survey of decentralized control methods

An overview is presented of the types of problems that are being considered by control theorists in the area of dynamic large scale systems with emphasis on decentralized control strategies. Approaches that deal directly with decentralized decision making for large scale systems are discussed. It is shown that future advances in decentralized system theory are intimately connected with advances in the stochastic control problem with nonclassical information pattern. The basic assumptions and mathematical tools associated with the latter are summarized, and recommendations concerning future research are presented.

Athans, M.↗
NASA NTRS1976

Stability analysis of combined continuous and discrete systems

A discrete, time-invariant system is represented by an equivalent continuous, periodic system. A combined continuous plant and discrete controller may then be formulated as a single continuous, periodic coefficient system. The exact stability solution for the combined system is obtained, as a matrix eigenvalue problem. Periodic system theory also gives some information about the type of instabilities which may be encountered in the combined plant and controller.

Johnson, W.↗
NASA NTRS1981

The reduced order model problem in distributed parameter systems adaptive identification and control

The basic assumption that a large space structure can be decoupled preceding the application of reduced order active control was considered and alternative solutions to the control of such structures (in contrast to the strict modal control) were investigated. The transfer function matrix from the actuators to the sensors was deemed to be a reasonable candidate. More refined models from multivariable systems theory were studied and recent results in the multivariable control field were compared with respect to theoretical deficiencies and likely problems in application to large space structures.

Johnson, C. R., Jr.↗
NASA NTRS1981

Kinematic properties of rotary-wing and fixed-wing aircraft in steady coordinated high-g turns

An analytical approach to the study of flight dynamics of aircraft operating in a high-angle-of-attack flight regime and of helicopters operating in extreme thrust conditions is presented. Steady coordinated high-g turns are used to establish the initial equilibrium flight conditions near stall angles of attack. The kinematic properties of the aircraft in steady coordinated turns are examined: in high-g turns, pitch rate (independent of the angle of attack) is of a much larger magnitude than roll and yaw rate; a substantial roll rate is found to develop in steep turns for all angles of attack; the angle of attack also has a significant effect on the pitch attitude, with decreasing influence as the normal load factor increases. The exact small disturbance equations of motion of the aircraft in general steady turns are also developed for application to both rotary-wing and fixed-wing aircraft in extreme conditions. These equations are in a first-order, vector-matrix format, and are thus compatible with many efficient software packages developed in modern system theory.

Chen, R. T. N.↗
NASA NTRS1982

Oceanographic applications of the Kalman filter

The Kalman filter is a data-processing algorithm with a distinguished history in systems theory. Its application to oceanographic problems is in the embryo stage. The behavior of the filter is demonstrated in the context of an internal equatorial Rossby wave propagation problem.

Barbieri, R. W.↗
NASA NTRS1983

Efficient Algorithms for Computing Trim and Small-Disturbance Equations of Motion of Aircraft Coordinated and Uncoordinated, Steady, Steep Turns

The development of computational algorithms that permit efficient calculation of aircraft trim states and of the associated small disturbance equations of motion for a systematic investigation of the statics and dynamics of aircraft in coordinated and uncoordinated, steady, steep turning flight is reported. The efficiency in the trim computation is realized by decoupling the governing equations. The small disturbance equations of motion, which are given in a general body axis system, include aerodynamic acceleration derivatives; they are cast in a familiar first order, vector matrix format of modern system theory. These algorithms were applied to a variety of rotorcraft simulation models. Results pertaining to a simulated hingeless rotor helicopter are also presented

Chen, Robert T. N.↗
NASA NTRS1984

Optimal quasi-static shape control for large aerospace antennae

In this paper, an on-line control approach which will adjust the steady-state shape of a large antenna arbitarily close to any achievable desired profile is proposed. The method makes use of distributed parameter system theory and allows refocusing using a limited number of control actuators and sensors. The controller gains are calculated by approximating the solution to an infinite-dimensional optimal quasi-static control problem. A very general convergence result for such quasi-static controllers is proved and applied to the antenna controller to show convergence, using any Galerkin (finite-element) approximation method.

Balas, M. J.↗
NASA NTRS1985

Robust Control Design for Large Space Structures

The control design problem for the class of future spacecraft referred to as large space structures (LSS) is by now well known. The issue is the reduced order control of a very high order, lightly damped system with uncertain system parameters, particularly in the high frequency modes. A design methodology which incorporates robustness considerations as part of the design process is presented. Combining pertinent results from multivariable systems theory and optimal control and estimation, LQG eigenstructure assignment and LQG frequency shaping, were used to improve singular value robustness measures in the presence of control and observation spillover.

Eastman, W. L.↗
NASA NTRS1983

Pfaffian systems and feedback linearization/obstructions

The concept of Cartan-Vessiot filtered Lie algebra/module is defined in terms of previous feedback linearizations constructed through canonical forms of Pfaffian systems associated with nonlinear systems. Nonlinearization/Cartan-Vessiot algebras are regarded as deformations of linear ones. It is shown how certain problems of interest in nonlinear system theory translate over to algebraic problems involving this sort of algebraic structure.

Hermann, R.↗