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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 91 records · Page 5

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NASA NTRS1976

Compensated control loops for a 30-cm ion thruster

The vaporizer dynamic control characteristics of a 30-cm diameter mercury ion thruster were determined by operating the thruster in an open loop steady state mode and then introducing a small sinusoidal signal on the main, cathode, or neutralizer vaporizer current and observing the response of the beam current, discharge voltage, and neutralizer keeper voltage, respectively. This was done over a range of frequencies and operating conditions. From these data, Bode plots for gain and phase were made and mathematical models were obtained. The Bode plots and mathematical models were analyzed for stability and appropriate compensation networks determined. The compensated control loops were incorporated into a power processor and operated with a thruster. The time responses of the compensated loops to changes in set points and recovery from arc conditions are presented.

Robson, R. R.↗

NASA NTRS1976

On the optimal minimum order observer-based compensator and the limited state variable feedback controller

Four design problems are considered: two on the optimal minimum order observer-based compensator design and two on the optimal limited state variable feedback controller. The problem of designing an optimal discrete time linear time-invariant observer-based compensator for the regulation of an n dimensional linear discrete time time-invariant plant with m independent outputs is considered. This is a stochastic design problem to the extent that the initial plant state is assumed to be a random vector with known first and second order statistics. The compensator parameters are obtained by minimizing the expectation, with respect to the initial conditions, of the standard cost, quadratic in the state and control vectors with the inclusion of cross terms.

Llorens-Ortiz, B.↗

NASA NTRS1976

Compensated control loops for a 30-cm ion thruster

Robson, R. R.↗

NASA NTRS1978

Invariants of optimal minimal-order observer-based compensators

The relations characterizing the optimal minimal-order observer-based compensators for a linear time-invariant multivariable system with a random initial state (or, equivalently, known initial state and white plant-driving noise) have been reported by Miller (1973). In this note we establish in general that the plant transfer function uniquely determines the optimal compensator transfer function, and that this characterizes precisely the degrees of freedom in the compensator design; computational implications of this result are indicated.

Blanvillain, P. J.↗

NASA NTRS1979

The discrete-time compensated Kalman filter

A suboptimal dynamic compensator to be used in conjunction with the ordinary discrete-time Kalman filter is derived. The resultant compensated Kalman filter has the property that steady-state bias estimation errors, resulting from modelling errors, are eliminated. The implementation of the compensated Kalman filter involves the use of accumulators in the residual channels in addition to the nominal dynamic model of the stochastic system.

Lee, W.-H.↗

NASA NTRS1979

Issues in the digital implementation of control compensators

Techniques developed for the finite-precision implementation of digital filters were used, adapted, and extended for digital feedback compensators, with particular emphasis on steady state, linear-quadratic-Gaussian compensators. Topics covered include: (1) the linear-quadratic-Gaussian problem; (2) compensator structures; (3) architectural issues: serialism, parallelism, and pipelining; (4) finite wordlength effects: quantization noise, quantizing the coefficients, and limit cycles; and (5) the optimization of structures.

Moroney, P.↗

NASA NTRS1981

Spacecraft attitude pointing performance during orbit adjust as a function of compensator order

A steady state compensator of specified order is proposed to estimate the required duty cycle needed to balance the distribution torque. The compensator was increased gradually to demonstrate the improvement in pointing accuracy. The basic mathematical model of the flexible spacecraft and sensor used to characterize the performance of the compensator are described.

Basuthakur, S.↗

NASA NTRS1982

An image drift compensation system for a solar pointed space telescope

Two sounding rocket test flights have been conducted in the development of an image drift compensation system designed for a solar-pointed space telescope. The system, whose scientific results are presented, employs limb-sensing photodiodes at the telescope focal plane and provides drift compensation to better than + or - 0.1 arcsec. A variation of this device will be employed by the Space Shuttle/Spacelab 2 flight of the High Resolution Telescope and Spectrograph (HRTS) Instrument. The data gathered by the rocket flights of the drift compensation system have revealed high velocity ejecta traveling through the transition zone and corona at velocities up to 400 km/sec. The HRTS configuration and its constitutive instruments' optical parameters are described.

Bartoe, J.-D. F.↗

NASA NTRS1982

An optimal control model approach to the design of compensators for simulator delay

The effects of display delay on pilot performance and workload and of the design of the filters to ameliorate these effects were investigated. The optimal control model for pilot/vehicle analysis was used both to determine the potential delay effects and to design the compensators. The model was applied to a simple roll tracking task and to a complex hover task. The results confirm that even small delays can degrade performance and impose a workload penalty. A time-domain compensator designed by using the optimal control model directly appears capable of providing extensive compensation for these effects even in multi-input, multi-output problems.

Baron, S.↗

NASA NTRS1983

Dynamic isolation via momentum compensation for precision instrument pointing

The concept of a momentum-compensated inertially stabilized platform (IPPADS) for carrying scientific instruments is presented, the platform's function as a mechanical diode is explained, and the implications of momentum compensation for platform pointing and cost are discussed. The equations of motion for momentum compensation in the IPPADS five-body system are derived, and the results are used to computer simulate the system under consideration with two examples.

Boussalis, D.↗

NASA NTRS1986

Photo Hall-effect characterization of closely compensated Ge:Be

The temperature dependence of the free-carrier concentration in germanium doped with the double acceptor Be has been investigated using the photo Hall-effect technique and found to be strongly temperature dependent when the residual shallow impurities are closely compensated. Close compensation of shallow levels was achieved by controlling the concentration of a beryllium-hydrogen acceptor complex A(Be,H) which is present in crystals grown under a H2 atmosphere. This complex can be removed with high-temperature annealing. An increase of up to two orders of magnitude in free-carrier lifetime as a function of temperature is found to occur between 5 and 11 K in closely compensated material due to the population inversion of ionized centers created by optical pumping.

Germer, T. A.↗

NASA NTRS1987

Approximation of discrete-time LQG compensators for distributed systems with boundary input and unbounded measurement

The approximation of optimal discrete-time linear quadratic Gaussian (LQG) compensators for distributed parameter control systems with boundary input and unbounded measurement is considered. The approach applies to a wide range of problems that can be formulated in a state space on which both the discrete-time input and output operators are continuous. Approximating compensators are obtained via application of the LQG theory and associated approximation results for infinite dimensional discrete-time control systems with bounded input and output. Numerical results for spline and modal based approximation schemes used to compute optimal compensators for a one dimensional heat equation with either Neumann or Dirichlet boundary control and pointwise measurement of temperature are presented and discussed.

Gibson, J. S.↗

NASA NTRS1987

The effect of a shallow low viscosity zone on the apparent compensation of midplate swells

A model for midplate swells is assumed where the swell topography is dynamically maintained by convection beneath a conducting lid. Using an idealized viscosity structure consisting of a low viscosity layer underneath the lid and overlying a constant viscosity region, the effect of the low viscosities, the layer thickness, and the Rayleigh number on the flow and on the inference of a compensation mechanism from the associated gravity, geoid, and topography anomalies is investigated. The calculations show that a simple plume model with stratified viscosity variations of less than two orders of magnitude near the surface can produce the range of depths of compensation seen at midplate swells. Shallow depths of compensation, therefore, cannot be used to argue against dynamic models for the formation of hot spot swells.

Robinson, Elizabeth M.↗

NASA NTRS1988

The Design and Use of a Temperature-Compensated Hot-Film Anemometer System for Boundary-Layer Flow Transition Detection on Supersonic Aircraft

An airborne temperature-compensated hot-film anemometer system has been designed, fabricated, and used to obtain in-flight airfoil boundary-layer flow transition data by the NASA Ames-Dryden Flight Research Facility. Salient features of the anemometer include near constant sensitivity over the full flight envelope, installation without coaxial wiring, low-noise outputs, and self-contained signal conditioning with dynamic and steady-state outputs. The small size, low-power dissipation, and modular design make the anemometer suitable for use in modern high-performance research aircraft. Design of the temperature-compensated hot-film anemometer and its use for flow transition detection on a laminar flow flight research project are described. Also presented are data gathered in flight which is representative of the temperature-compensated hot-film anemometer operation at subsonic, transonic, and supersonic flight conditions.

Chiles, Harry R.↗

NASA NTRS1988

An approximate loop transfer recovery method for designing fixed-order compensators

A method for designing fixed-order dynamic compensators for multivariable time invariant linear systems is presented which is based on the minimization of a linear quadratic performance index. The present formulation is performed in an output feedback setting which uses an observer cononical form to represent the compensator dynamics. Techniques for penalizing the plant and compensator states and for selecting the distribution on initial conditions such that the loop transfer matrix approximates that of a full-state feedback design have been developed. The effectiveness of the method is demonstrated using the examples of the pointing of a flexible structure and a helicopter flight control problem.

Calise, Anthony J.↗

NASA NTRS1988

Approximation of discrete-time LQG compensators for distributed systems with boundary input and unbounded measurement

The approximation of optimal discrete-time linear quadratic Gaussian (LQG) compensators for distributed parameter control systems with boundary input and unbounded measurement is considered. The approach applies to a wide range of problems that can be formulated in a state space on which both the discrete-time input and output operators are continuous. Approximating compensators are obtained via application of the LQG theory and associated approximation results for infinite dimensional discrete-time control systems with bounded input and output. Numerical results for spline and modal based approximation schemes used to compute optimal compensators for a one-dimensional heat equation with either Neumann or Dirichlet boundary control and pointwise measurement of temperature are presented and discussed.

Gibson, J. S.↗

NASA NTRS1989

Adaptive feed array compensation system for reflector antenna surface distortion

The feasibility of a closed loop adaptive feed array system for compensating reflector surface deformations has been investigated. The performance characteristics (gain, sidelobe level, pointing, etc.) of large communication antenna systems degrade as the reflector surface distorts mainly due to thermal effects from a varying solar flux. The compensating systems described in this report can be used to maintain the design performance characteristics independent of thermal effects on the reflector surface. The proposed compensating system employs the concept of conjugate field matching to adjust the feed array complex excitation coefficients.

Acosta, Roberto J.↗

NASA NTRS1987

The dual element method of strain gauge temperature compensation

The use of a known temperature compensation technique is suggested to reduce the overall temperature sensitivity of a PdCr strain gauge system being developed for turbine engine research. The temperature compensation technique proposed for this application uses a resistance thermometer in an adjacent leg of the strain gauge bridge circuit to cancel the thermally generated resistance change of the strain gauge. Equations for calculating the required compensation resistor values and the sensitivity of the resulting strain gauge bridge to both temperature and strain are presented.

Englund, David R.↗