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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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ESS telecommunication system concept provides the ability to change according to needs indicated by the data without any change to the lunar experiment equipment. The system will include a magnetic core memory as the data multiplexing control device.
Application of the aerodynamic energy approach to some problems of flutter suppression and gust alleviation were considered. A simple modification of the control-law is suggested for achieving the required pitch control in the use of a leading edge - trailing edge activated strip. The possible replacement of the leading edge - trailing edge activated strip by a trailing edge - tab strip is also considered as an alternate solution. Parameters affecting the performance of the activated leading edge - trailing edge strip were tested on the Arava STOL Transport and the Westwind Executive Jet Transport and include strip location, control-law gains and a variation in the control-law itself.
Flight research has shown the effectiveness of adaptive flight controls for improving aircraft safety and performance in the presence of uncertainties. The National Aeronautics and Space Administration's (NASA)'s Integrated Resilient Aircraft Control (IRAC) project designed and conducted a series of flight experiments to study the impact of variations in adaptive controller design complexity on performance and handling qualities. A novel complexity metric was devised to compare the degrees of simplicity achieved in three variations of a model reference adaptive controller (MRAC) for NASA's F-18 (McDonnell Douglas, now The Boeing Company, Chicago, Illinois) Full-Scale Advanced Systems Testbed (Gen-2A) aircraft. The complexity measures of these controllers are also compared to that of an earlier MRAC design for NASA's Intelligent Flight Control System (IFCS) project and flown on a highly modified F-15 aircraft (McDonnell Douglas, now The Boeing Company, Chicago, Illinois). Pilot comments during the IRAC research flights pointed to the importance of workload on handling qualities ratings for failure and damage scenarios. Modifications to existing pilot aggressiveness and duty cycle metrics are presented and applied to the IRAC controllers. Finally, while adaptive controllers may alleviate the effects of failures or damage on an aircraft's handling qualities, they also have the potential to introduce annoying changes to the flight dynamics or to the operation of aircraft systems. A nuisance rating scale is presented for the categorization of nuisance side-effects of adaptive controllers.
This paper presents an adaptive control approach to enhance the performance of current attitude control system used by the Space Station Freedom. The proposed control law was developed based on the direct adaptive control or model reference adaptive control scheme. Performance comparisons, subject to inertia variation, of the adaptive controller and the fixed-gain linear quadratic regulator currently implemented for the Space Station are conducted. Both the fixed-gain and the adaptive gain controllers are able to maintain the Station stability for inertia variations of up to 35 percent. However, when a 50 percent inertia variation is applied to the Station, only the adaptive controller is able to maintain the Station attitude.
Sensitivity to variations in electrical and mechanical characteristics reduced. Proposed control system for motor-driven rotary actuator includes three nested feedback loops which, when properly designed, decoupled from each other. Intended to increase accuracy of control by mitigating such degrading effects as vibrations and variations in electrical and mechanical characteristics of structure rotated. Lends itself to optimization of performance via independent optimization of each of three loops. Includes outer, actuator, and driver feedback loops, configured so that actuator is subsystem, and driver is subsystem of actuator.
The effects of small parameter variations on the performance index of optimal control systems with initial and final target manifolds, free end time, and bang-bang control are analyzed in this paper. A new approach to the sensitivity equation is presented. This approach takes into account the pulse-shaped variation produced by the parameter change on the bang-bang control. An expression, that relates the variations of the performance index, the trajectory, the final time, and the parameter, is derived. This expression extends to the class of optimal systems with bang-bang control, a result previously obtained by Courtin and Rootenberg (1971).
A ground-simulation experiment was conducted to investigate the direct and interactive influences of several longitudinal static and dynamic stability parameters on helicopter flying qualities during terminal-area operations in instrument conditions. Variations that were examined included five levels of static control-position gradients ranging from stable to unstable; two levels of dynamic stability for the long-period oscillation; two levels of the steady-state pitch speed gradient; two levels of angle-of-attack stability and pitch-rate damping; and two levels of stability and control augmentation. These variations were examined initially in calm air and thin in simulated light-to-moderate turbulence and wind shear. Five pilots performed a total of 223 evaluations of these parameters for a representative microwave landing system precision approach task conducted in a dual-pilot crew-loading situation.
Measurement of neutral N2, O, and He densities from Ogo 6 over the south polar region during magnetically quiet periods in late August and early September 1969. It is found that N2 densities, when they are extrapolated to a common altitude, maximize at about 0800 UT near 70 deg invariant latitude. The density of He has a minimum at this time, and the density of O has a slight maximum. It is proposed that these phenomena are the result of cyclic variations in soft electron precipitation, which heats the thermosphere either directly or through enhanced Joule heating. This heat energy would increase the gas temperature, the increase in the gas temperature leading to the N2 increase, and would vary the composition by generation of a wind system.
An analytical study has been made to determine the effects of mass-loading variations and onboard rotating machinery on a hypothetical earth-satellite space station, rotating to provide an artificial gravity equal to one-fourth of that at the earth's surface. Attempts were also made to damp out or minimize undesirable motions by using mass shifts, constant-rate inertia wheels, or jet-reaction moments. Results obtained indicate that the shifting of masses within the rotating space station could bring about large roll oscillations (plus or minus 100 degrees) or even continuous rolling motions if the craft is rotating about the axis of intermediate moment of inertia. The pitch angles obtained were generally small (less than plus or minus 1 degree). The amplitudes of the roll and pitch oscillations are dependent upon the angle of displacement of the greatest principal axis of inertia from the initial spin axis. In attempting to damp out or minimize undesirable motions, it was found that a constant-rate inertia wheel located on and rotating about the axis about which the craft is rotating (Z-axis) was beneficial in keeping the roll angles relatively small, provided it had a sufficient amount of angular momentum. It was also found that the use of jet-reaction moments was very satisfactory for damping undesirable motions in that the roll oscillations could be damped.
As a preliminary step in an investigation of control-stick vibration in direct-control autogiros, the periodic variations in the moments transmitted through the control system of a YG-1B autogiro were recorded in flight. The results of the measurements are presented in the form of coefficients of Fourier series expressing the varying part of the lateral and the longitudinal moments acting between rotor and fuselage at the control trunnions. The most important component of the variation in stick force was found to have frequency of three times the rotor speed and an amplitude that rose from negligible values at tip-speed ratio below 0.20 to +/-5.2 pounds longitudinally and +/-3.2 pounds laterally at tip-speed ratios of 0.35. Variations in stick force at all other frequencies were small in comparison with those at three times the rotor speed.
The perfect noninteraction for a discrete parameter set is examined along with the sensitivity of a decoupled flight control system with respect to system parameter variations. A set of computer programs developed for this project are described.
A bibliography is presented of publications and reports resulting from the research project.
Lower stratospheric air trajectories entering the region over Alaska at the approximately 125 mb level during late May, 1975 indicate a substantial shift in the geographical source regions for the air masses present during that time. This shift coincides with an approximately 25% decrease in the observed halocarbon mixing ratios at the 125 mb level as determined from a daily sequence of halocarbon profiles. Since the halocarbon species measured are essentially chemically inactive at this level, the observed variation is linked to the changing meteorological pattern.
Adaptive control is presently one of the methods available which may be used to control plants with poorly modelled dynamics or time varying dynamics. Although many variations of adaptive controllers exist, a common characteristic of all adaptive control schemes, is that input/output measurements from the plant are used to adjust a control law in an on-line fashion. Ideally the adjustment mechanism of the adaptive controller is able to learn enough about the dynamics of the plant from input/output measurements to effectively control the plant. In practice, problems such as measurement noise, controller saturation, and incorrect model order, to name a few, may prevent proper adjustment of the controller and poor performance or instability result. In this work we set out to avoid the inadequacies of procedurally implemented safety nets, by introducing a two level control scheme in which an expert system based 'supervisor' at the upper level provides all the safety net functions for an adaptive controller at the lower level. The expert system is based on a shell called IPEX, (Interactive Process EXpert), that we developed specifically for the diagnosis and treatment of dynamic systems. Some of the more important functions that the IPEX system provides are: (1) temporal reasoning; (2) planning of diagnostic activities; and (3) interactive diagnosis. Also, because knowledge and control logic are separate, the incorporation of new diagnostic and treatment knowledge is relatively simple. We note that the flexibility available in the system to express diagnostic and treatment knowledge, allows much greater functionality than could ever be reasonably expected from procedural implementations of safety nets. The remainder of this chapter is divided into three sections. In section 1.1 we give a detailed review of the literature in the area of supervisory systems for adaptive controllers. In particular, we describe the evolution of safety nets from simple ad hoc techniques, up to the use of expert systems for more advanced supervision capabilities.
Optimal trajectory and control approximate solution by asymptotic expansion, considering Mayer variational problem solution
This paper proposes a communication-less synchronization and output power control strategy for LCC-LC compensated inductive power transfer systems with a secondaryside active rectifier. By replacing the passive rectifier with an active bridge, the proposed architecture eliminates the need for a separate secondary-side DC-DC converter and enables direct regulation of battery power. The key challenge in such a system is achieving robust synchronization of the secondary active bridge with the primary inverter without access to primary-side signals. To address this issue, the secondary-side variables are analyzed and the current through the secondary series inductor is identified as a load-independent synchronization variable with a fixed phase relationship to the primary excitation. A fixed-frequency second order generalized (SOGI)-based phase locked loop (PLL) is used to estimate the switching phase and frequency, and a phase-shift-based output power controller is developed using a phasor-transformer model of the active bridges. A modified control formulation is further introduced to remove phase-dependent loop-gain variation and simplify controller design. Simulation results validate the proposed method under both fixed and varying switching-frequency conditions, demonstrating successful frequency tracking from 82 kHz to 88 kHz and accurate output power regulation over a wide operating range. The proposed method offers a compact and effective solution for high-power IPT systems by enabling secondary-side synchronization and control without wireless communication or an additional DC-DC conversion stage.
Development of a digital control system dynamic variation technique which accounts for the limitation of available frequency response analyzers. Digital control system theory is briefly reviewed, and generation of the necessary theoretical frequency responses is discussed. Results of the dynamic verification of a digital control system for a Saturn V launch vehicle are presented, and attention is given to the limitations of this technique along with its applicability to other types of digital control systems. A technique for performing open-loop frequency response analyses of a flight program implemented in a 'flight-type' digital computer and interface hardware with vehicle dynamics simulated on an analog computer is described.
A comparison of prints from ERTS photography revealed significant differences in the image quality produced at GSFC, the EROS facility at Sioux Falls, and Eastman Kodak in Rochester. Based on this survey photographic quality was improved significantly at Sioux Falls, and improvements were suggested for optical and contact printers at the GSFC. Based on a test in which 365 meters of Eastman Electron Recording Film (ESTAR Base) SO-438 were processed the 1-sigma variation in process control from all sources is about + or - 0.04 at a density of 1.0. Variations from film and from processing were approximately equal contributors to the overall tolerance. Distortion produced by the Kodak Colorado printer at GSFC covers a range of about 0.04%, a small value compared to that caused by other factors in the ERTS system. The edge fringing inherent in the color film materials used at GSFC also seems to be a small factor in the unsharpness of ERTS color prints. MTF and granularity measurements were made on processed film samples supplied by GSFC. MTF values were above 0.70 out to 42 cycles/mm for all stages of contact printing in the ERTS system.