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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Multivariable closed loop control analysis and synthesis for complex flight systems

A flight control system analysis and synthesis method is presented that is intended to be especially suitable for application to vehicles exhibiting complex dynamic characteristics. For such vehicles quantitative handling qualities specifications are not usually available. Howver, handling qualities objectives are specifically introduced in this method via the hypothesis of correlation between pilot ratings and the objective function of an optimal control model of the human pilot. Further, since augmentation and pilot operate in parallel, simultaneous determination of the augmentation and pilot model gains is required. Desirable augmented dynamics are obtained for a variety of complex systems and the method is experimentally verified in the case of simple pilot damper gain selection for optimum pitch tracking performance.

Schmidt, D. K.↗
NASA NTRS1980

Nutritional criteria for closed-loop space food systems

The nutritional requirements for Skylab crews are summarized as a data base for long duration spaceflight nutrient requirements. Statistically significant increases in energy consumption were detected after three months, along with CO2/O2 exhalation during exercise and thyroxine level increases. Linoleic acid amounting to 3-4 g/day was found to fulfill all fat requirements, and carbohydrate and protein (amino acid) necessities are discussed, noting that vigorous exercise programs avoid deconditioning which enhances nitrogen loss. Urinary calcium losses continued at a rate 100% above a baseline figure, a condition which ingestion of vitamin D2 did not correct. Projections are given that spaceflights lasting more than eight years will necessitate recycling of human waste for nutrient growth, which can be processed into highly efficient space food with a variety of tastes.

Rambaut, P. C.↗
NASA NTRS1982

Absorption of carbon dioxide by solid hydroxide sorbent beds in closed-loop atmospheric revitalization system

The reactions of carbon dioxide with various metals are discussed. The equations which govern the rates of CO2 removal from the atmosphere in spacecraft environmental control systems are discussed. Results from performance testing of various Space Shuttle environmental control systems are presented with the correlation of the equations to the performance given.

Davis, S. H., Jr.↗
NASA NTRS1983

Pilot modeling and closed-loop analysis of flexible aircraft in the pitch tracking task

The issue addressed in the appropriate modeling technique for pilot vehicle analysis of large flexible aircraft, when the frequency separation between the rigid-body mode and the dynamic aeroelastic modes is reduced. This situation was shown to have significant effects on pitch-tracking performance and subjective rating of the task, obtained via fixed base simulation. Further, the dynamics in these cases are not well modeled with a rigid-body-like model obtained by including only 'static elastic' effects, for example. It is shown that pilot/vehicle analysis of this data supports the hypothesis that an appropriate pilot-model structure is an optimal-control pilot model of full order. This is in contrast to the contention that a representative model is of reduced order when the subject is controlling high-order dynamics as in a flexible vehicle. The key appears to be in the correct assessment of the pilot's objective of attempting to control 'rigid-body' vehicle response, a response that must be estimated by the pilot from observations contaminated by aeroelastic dynamics. Finally, a model-based metric is shown to correlate well with the pilot's subjective ratings.

Schmidt, D. K.↗
NASA NTRS1984

Linear distributed parameter systems - Closed-loop exponential stability with a finite-dimensional controller

Theoretical results are presented which characterize the linear distributed parameter system (DPS) which can be (exponentially) stabilized by a finite-dimensional controller. This characterization relies on stabilizing subspaces and the solvability of the nonlinear asymmetric Riccati equation. Also considered are connections with the usual model reduction approaches to finite-dimensional DPS controller design.

Balas, M. J.↗
NASA NTRS1985

A model of flow in a closed-loop thermosyphon including the Soret effect

This theoretical study addresses the nature of convective motions in a toroidal loop of binary fluid oriented in the vertical plane and heated from below. The boundaries of the loop are impermeable, but gradients of the solute can be set up by Soret diffusion in the direction around the loop. The existence and stability of steady solutions are discussed over the Rayleigh number-Soret coefficient parameter plane. When the Soret coefficient is negative, periodic and chaotic oscillations analogous to those of thermohaline convection are predicted. When the Soret coefficient is positive, relaxation oscillations and low Rayleigh number chaotic motions are found. Both sets of phenomena are predicted to occur for realistic thermosyphon parameters.

Hart, J. E.↗
NASA NTRS1986

Design and simulation of closed-loop ground alignment of inertial platforms with sway motion

This paper is concerned with the application of optimal estimation and control concepts to the ground alignment of inertial platforms subjected to random sway motion. A seventh-order Kalman filter has been designed for estimating the platform misalignments and sway motion. Using the linear quadratic optimal regulator techniques, feedback controller gains have been designed to drive the initial misalignments to a small value. A reconfiguration of the filter controller scheme has been proposed and verified by Monte Carlo simulation for improving the speed of alignment without changing the alignment accuracy.

Vathsal, S.↗
NASA NTRS1987

Closed loop fiber optic rotation sensor

An improved optical gyroscope is provided, of the type that passes two light components in opposite directions through an optic fiber coil, and which adds a small variable frequency to one of the light components to cancel the phase shift due to rotation of the coil. The amount of coil rotation from an initial orientation, is accurately determined by combining the two light components, one of which has a slightly increased frequency, to develop beats that each represent a predetermined angle of rotation. The direction of rotation is obtained by combining the two light components on a photodetector, intermittently phase shifting a single light component by 90 deg and comparing the direction of change of photodetector output (+ or -) caused by the 90 deg shift, with the slope (+ or -) of the photodetector output at about the same time, when there is a 90 deg shift.

Goss, Willis C.↗
NASA NTRS1986

A review of modelling techniques for the open and closed-loop dynamics of large space systems

This paper reviews the steps in the development of mathematical models that can be used to simulate the in-orbit dynamic behavior of large flexible systems. A general continuum formulation is compared with the hybrid coordinate formulation and also a finite element representation of the total system. A review of structural analysis routines emphasizes the use of computer generated graphics to help understand the different modal elastic shape functions of complex systems. Numerical techniques employed to synthesize shape and attitude control laws are summarized. Finally, the modeling of environmental disturbance torques due to the interaction of solar radiation pressure on vibrating and thermally deflected systems is discussed.

Bainum, Peter M.↗
NASA NTRS1988

Closed-Loop Optical Rotation Sensor

Optical/electronic system senses rotation and emits pulses at angular increments. System provides linear scale factor across wide range of rotation rates with no lockup at null. Design needs analog-to-digital converters with elaborate signal-processing circuits. Light from laser diode split evenly into two beams propagating in opposite directions around rotation-sensing coil of optical-fiber waveguide. Beams acquire phase difference proportional to rotation rate as they pass through coil. After emerging from coil, beams recombine in beam splitter, and coherent sum led to photodiode.

Goss, Willis C.↗
NASA NTRS1989

Closed-Loop Motor-Speed Control

Electronic motor-speed control circuit designed to operate in electrically noisy environment. Includes optoelectronic pick-up device, placed inside motor housing to provide speed feedback signal. Automatically maintains speed motor at commanded value. Measures speed of motor in terms of frequency of pulses of infrared light chopped by fan blades of motor. Difference between measured and commanded speeds serves as control signal for external amplifier driving motor. Major advantage of circuit is low cost.

Smith, Matthew A.↗
NASA NTRS1990

Design of Sensors for Control of Closed Loop Life Support Systems

A brief summary is presented of a Engineering Design sequence, a cooperation between NASA-Kennedy and the University of Florida on the Controlled Environmental Life Support System (CELSS) program. Part of the class was devoted to learning general principles and techniques of design. The next portion of the class was devoted to learning to design, actually fabricating and testing small components and subsystems of a CELSS.

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