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At least 757 records · Page 42

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NASA NTRS1972

Analysis of legged landers for the survivable soft landing of instrument payloads.

Two methods of analysis have been developed for legged planetary landers. The first of these, the Large Displacement Gear Analysis, is a design tool for statically determining the large displacement stroking behavior, energy absorption characteristics, and internal load distributions in a single gear. The second, the Landing Dynamics Analysis, predicts the spatial landing dynamics of a legged lander. Effects of structural flexibility, elastic-plastic gear load characteristics, and soil properties on the loads, motions, and stability of the lander may be determined. Validation of the analytical techniques is accomplished through comparison of predicted results and experimental data obtained during a model test program.

Laurenson, R. M.↗

NASA NTRS1972

Study of buoyancy systems for flight vehicles

The performance potential of buoyant systems and flexible structures used in air vehicles for short-haul passenger transportation is discussed. The study was intended only to determine if sufficient performance potential existed, and to provide a focus for a more extensive design study, if such a study appeared desirable. A relatively conventional helium system was examined along with a more unusual configuration employing hot-air as the buoyant fluid. Both configurations were examined in the VTOL and STOL modes of operation. The helium system appears to have some superiority in the VTOL mode, while the hot-air system has a superiority in the STOL mode. Both configurations exhibit sufficient performance potential to suggest that a much more extensive design study might well be undertaken.

Havill, C. D.↗

NASA NTRS1973

French wind generator systems

The experimental design of a wind driven generator with a rated power of 800 kilovolt amperes and capable of being connected to the main electrical network is reported. The rotor is a three bladed propeller; each blade is twisted but the fixed pitch is adjustable. The asynchronous 800-kilovolt ampere generator is driven by the propeller through a gearbox. A dissipating resistor regulates the machine under no-load conditions. The first propeller on the machine lasted 18 months; replacement of the rigid propeller with a flexible structure resulted in breakdown due to flutter effects.

Noel, J. M.↗

NASA NTRS1976

FLEXSTAB: A computer program for the prediction of loads and stability and control of flexible aircraft

Capabilities of the FLEXSTAB Computer Program System are described and illustrated. Aeroelastic analysis of a wide variety of aircraft configurations is performed. The aerodynamic theory used in FLEXSTAB is applicable to both steady and unsteady, subsonic and supersonic flow for multiple wing-body tail nacelle configurations with a plane of symmetry. For unsteady flow calculations, an unsteady aerodynamic theory is used which is appropriate for the low reduced frequencies associated with aircraft flight dynamics. The aircraft is modeled as either a rigid or flexible structure. The computer trims the aircraft in steady reference flight and computes both static and dynamic stability and control derivatives and the stability behavior about the trim condition. The airplane lifting pressure distribution, aerodynamic and inertia loads and deflected shape are also computed.

Perkin, B. R.↗

NASA NTRS1977

Flap/Lag/Torsion Dynamics of a Uniform, Cantilever Rotor Blade in Hover

The dynamic stability of the flap/lag/torsion motion of a uniform, cantilever rotor blade in hover is calculated. The influence of blade collective pitch, lag frequency, torsional flexibility, structural coupling, and precone angle on the stability is examined. Good agreement is found with the results of an independent analytical investigation.

Johnson, W.↗

NASA NTRS1979

Method for forming a solar array strip

A flexible solar array strip is formed by a method which lends itself to automatic production techniques. Solder pads are deposited on printed circuitry deposited on a flexible structure. The resultant substrate is stored on a drum from which it is withdrawn and incrementally advanced along a linear path. Solderless solar cells are serially transported into engagement with the pads which are then heated in order to attach the cells to the circuitry. Excess flux is cleaned from the cells which are encapsulated in a protective coating. The resultant array is then spirally wound on a drum.

Mueller, R. I.↗

NASA NTRS1980

Attitude control study for a large flexible spacecraft using a Solar Electric Propulsion System (SEPS)

The attitude control performance of the solar electric propulsion system (SEPS) was evaluated. A thrust vector control system for powered flight control was examined along with a gas jet reaction control system, and a reaction wheel system, both of which have been proposed for nonpowered flight control. Comprehensive computer simulations of each control system were made and evaluated using a 30 mode spacecraft model. Results obtained indicate that thrust vector control and reaction wheel systems offer acceptable smooth proportional control. The gas jet control system is shown to be risky for a flexible structure such as SEPS, and is therefore, not recommended as a primary control method.

Tolivar, A. F.↗

NASA NTRS1980

Hardware demonstration of flexible beam control

An experiment employing a pinned-free flexible beam has been constructed to demonstrate and verify several facets of the control of flexible structures. The desired features of the experiment are to demonstrate active shape control, active dynamic control, adaptive control, various control law design approaches, and associated hardware requirements and mechanization difficulties. This paper contains the analytical work performed in support of the facility development, the final design specifications, control law synthesis, and some preliminary results.

Schaechter, D. B.↗

NASA NTRS1981

Application of constrained optimization to active control of aeroelastic response

Active control of aeroelastic response is a complex in which the designer usually tries to satisfy many criteria which are often conflicting. To further complicate the design problem, the state space equations describing this type of control problem are usually of high order, involving a large number of states to represent the flexible structure and unsteady aerodynamics. Control laws based on the standard Linear-Quadratic-Gaussian (LQG) method are of the same high order as the aeroelastic plant. To overcome this disadvantage of the LQG mode, an approach developed for designing low order optimal control laws which uses a nonlinear programming algorithm to search for the values of the control law variables that minimize a composite performance index, was extended to the constrained optimization problem. The method involves searching for the values of the control law variables that minimize a basic performance index while satisfying several inequality constraints that describe the design criteria. The method is applied to gust load alleviation of a drone aircraft.

Newsom, J. R.↗

NASA NTRS1981

Command profile for Galileo scan platform control

A recursive command profile is developed for the control of a two-degree-of-freedom scan platform mounted on a flexible structure. Perfect sensors and actuators are assumed for development and testing, and structural vibrations are minimized by actuator torque commands following a smooth torque-time profile. The integral of the smooth torque profile, the rate profile, is recursively generated by a piecewise constant second derivation, and the torque applied by the closk actuator is divided into three components. Results show that the smooth platform motion in response to the command profiles is what the Galileo control systems needs to avoid stator structural vibrations. Position, rate and acceleration profiles are also presented, and the resulting motion of the scan platform in response to command profiles is illustrated.

Man, G. K.↗

NASA NTRS1981

Tuned feedback damping with application to the Galileo spacecraft

An adaptive controller has been developed which uses phase-locked-loops as the adaptive devices. The controller provides active damping to systems which have their underdamped frequencies known only to within a particular range (e.g. plus or minus 20% uncertainty). The design and analysis of the controller is presented along with an application of such a controller to the scan platform pointing system of the Galileo spacecraft, a system with sensors and actuators separated by flexible structure.

Macala, G. A.↗

NASA NTRS1982

Control technology development

The main objectives of the control technology development task are given in the slide below. The first is to develop control design techniques based on flexible structural models, rather than simple rigid-body models. Since large space structures are distributed parameter systems, a new degree of freedom, that of sensor/actuator placement, may be exercised for improving control system performance. Another characteristic of large space structures is numerous oscillatory modes within the control bandwidth. Reduced-order controller design models must be developed which produce stable closed-loop systems when combined with the full-order system. Since the date of an actual large-space-structure flight is rapidly approaching, it is vitally important that theoretical developments are tested in actual hardware. Experimental verification is a vital counterpart of all current theoretical developments.

Schaechter, D. B.↗

NASA NTRS1981

Rotor systems research aircraft /RSRA/ rotor force and moment measurement system

The two Rotor Systems Research Aircraft (RSRA) are flight vehicles with unique measurement capabilities. The primary goal of the RSRA is direct measurement of rotor forces and moments in flight. This is accomplished through a rotor force and moment measurement system comprised of load cells and/or hydro-pneumatic isolator units which are integral to the aircraft structure. Due to structural flexibility, the aircraft must undergo a physical calibration. A static calibration of the first RSRA has been completed, and data analysis has progressed through determination of a linear calibration algorithm. Design, development, and operation of the RSRA rotor force and moment measurement system and the Static Calibration Facility are described, and results of the calibration are presented.

Burks, J. S.↗

NASA NTRS1982

Fokker-Planck response of stochastic satellites

The present investigation is concerned with the effects of stochastic geometry and random environmental torques on the pointing accuracy of spinning and three-axis stabilized satellites. The study of pointing accuracies requires a knowledge of the rates of error growth over and above any criteria for the asymptotic stability of the satellites. For this reason the investigation is oriented toward the determination of the statistical properties of the responses of the satellites. The geometries of the satellites are considered stochastic so as to have a phenomenological model of the motions of the flexible structural elements of the satellites. A widely used method of solving stochastic equations is the Fokker-Planck approach where the equations are assumed to define a Markoff process and the transition probability densities of the responses are computed directly as a function of time. The Fokker-Planck formulation is used to analyze the response vector of a rigid satellite.

Huang, T. C.↗

NASA NTRS1983

Adaptive control of a flexible beam using least square lattice filters

This paper presents an indirect adaptive control scheme for the control of flexible structures using recursive least square lattice filters. The identification scheme uses lattice filters which provide an on-line estimate of the number of modes, mode shapes and modal amplitudes. These modes are coupled and a transformation to decouple them in order to obtain the natural modes is presented. The decoupled modal amplitude time series are then used in an equation error identification scheme to identify the model parameters in an autoregressive moving average (ARMA) form. The control is based on modal pole placement scheme with the objective of vibration suppression. The control gains are calculated based on the identified ARMA parameters. Before using the identified parameters for control, detailed testing and validation procedures are carried out on the identified parameters. The full adaptive control scheme is demonstrated using the simulation for the 12 foot free-free beam apparatus at NASA Langley Research Center.

Sundararajan, N.↗

NASA NTRS1984

Control of large flexible spacecraft by the independent modal-space control method

The problem of control of a large-order flexible structure in the form of a plate-like lattice by the Independent Modal-Space Control (IMSC) method is presented. The equations of motion are first transformed to the modal space, thus obtaining internal (plant) decoupling of the system. Then, the control laws are designed in the modal space for each mode separately, so that the modal equations of motion are rendered externally (controller) decoupled. This complete decoupling applies both to rigid-body modes and elastic modes. The application of linear optimal control, in conjunction with a quadratic performance index, is first reviewed. A solution for high-order systems is proposed here by the IMSC method, whereby the problem is reduced to a number of modal minimum-fuel problems for the controlled modes.

Meirovitch, L.↗

NASA NTRS1984

Precise control of flexible manipulators

Experimental apparatus were developed for physically testing control systems for pointing flexible structures, such as limber spacecraft, for the case that control actuators cannot be collocated with sensors. Structural damping ratios are less than 0.003, each basic configuration of sensor/actuator noncollocation is available, and inertias can be halved or doubled abruptly during control maneuvers, thereby imposing, in particular, a sudden reversal in the plant's pole-zero sequence. First experimental results are presented, including stable control with both collocation and noncollocation.

Cannon, R. H., Jr.↗

NASA NTRS1984

Tools for active control system design

Efficient control law analysis and design tools which properly account for the interaction of flexible structures, unsteady aerodynamics and active controls are developed. Development, application, validation and documentation of efficient multidisciplinary computer programs for analysis and design of active control laws are also discussed.

Adams, W. M., Jr.↗