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Results for “feedback linearization”

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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Time-controlled descent guidance in uncertain winds

A procedure has been developed for constructing a statistical model of the altitude-dependent mean wind profile from the historical record of wind measurements at particular locations. The model is constructed by fitting a Markov process, with altitude as the stage variable, to the historical wind data. The wind model, together with the aircraft dynamics and the error characteristics of the navigation system, are incorporated in the design of a state estimator, which gives the minimum variance estimate of the aircraft state and the wind vector. The state and wind estimates are used as inputs to a linear feedback law for guiding the aircraft along the nominal trajectory. An example design of a time-constrained (4D RNAV) descent guidance system is presented, showing tracking accuracy, control activity, and probability of arrival time with and without the wind estimator.

Menga, G.↗
NASA NTRS1976

M-ary shift register

Binary devices are used to construct an m-ary linear feedback shift register.

Perlman, M.↗
NASA NTRS1975

Amplification of Reynolds number dependent processes by wave distortion

A system using a hot-wire transducer as an analog of a liquid droplet of propellant was employed to investigate the ingredients of the acoustic instability of liquid-propellant rocket engines. It was assumed that the combustion process was vaporization-limited and that the combustion chamber was acoustically similar to a closed-closed right-circular cylinder. Before studying the hot-wire closed-loop system (the analog system), a microphone closed-loop system, which used the response of a microphone as the source of a linear feedback exciting signal, was investigated to establish the characteristics of self-sustenance of acoustic fields. Self-sustained acoustic fields were found to occur only at resonant frequencies of the chamber. In the hot-wire closed-loop system, the response of hot-wire anemometer was used as the source of the feedback exciting signal. The self-sustained acoustic fields which developed in the system were always found to be harmonically distorted and to have as their fundamental frquency a resonant frequency for which there also existed a second resonant frequency which was approximately twice the fundamental frequency.

Ventrice, M. B.↗
NASA NTRS1976

Control of spinning flexible spacecraft by modal synthesis

A procedure is presented for the active control of a spinning flexible spacecraft. Such a system exhibits gyroscopic effects. The design of the controller is based on modal decomposition of the gyroscopic system. This modal decoupling procedure leads to a control mechanism implemented in modular form, which represents a distinct computational advantage over the control of the coupled system. Design procedures are demonstrated for two types of control algorithms, linear and nonlinear. The first represents classical linear feedback approach, and the second represents an application of on-off control, both types made feasible by the modal decomposition scheme.

Meirovitch, L.↗
NASA NTRS1975

Long frame sync words for binary PSK telemetry

Correlation criteria have previously been established for identifying whether a given binary sequence would be a good frame sync word for phase-shift keyed telemetry. In the past, the search for a good K-bit sync word has involved the application of these criteria to the entire set of 2 exponent K binary K-tuples. It is shown that restricting this search to a much smaller subset consisting of K-bit prefixes of pseudonoise sequences results in sync words of comparable quality, with greatly reduced computer search times for larger values of K. As an example, this procedure is used to find good sync words of length 16-63; from a storage viewpoint, each of these sequences can be generated by a 5- or 6-bit linear feedback shift register.

Levitt, B. K.↗
NASA NTRS1975

Guidance of an aeromaneuvering orbit-to-orbit shuttle through a statistically varying atmosphere

One candidate for a reusable upper stage to be carried by the space shuttle is an aeromaneuvering orbit-to-orbit shuttle (AMOOS). This concept uses the drag of the vehicle during a pass through the atmosphere rather than the propulsion system to slow the vehicle on a return from a high energy orbit. The nature and magnitude of the sensitivity of AMOOS to uncertainties in the properties of the atmosphere are shown. Various guidance schemes for correcting for the effects that the unpredictable variations in the atmosphere have on the trajectory are discussed. For the mission studied here, a payload retrieval from geosynchronous orbit with aerodynamic plane change, a linear feedback guidance scheme was developed. A relatively simple heuristic law was used to demonstrate the concept. Using optimal control theory a feedback law was developed analytically. Testing with a large number of different atmospheres showed this law to be a feasible means of controlling the AMOOS trajectory. Refinements to the technique offer promise of significant improvement, and these are discussed.

Rehder, J. J.↗
NASA NTRS1976

Control of spinning flexible spacecraft by modal synthesis

A procedure is presented for the active control of a spinning flexible spacecraft. Such a system exhibits gyroscopic effects. The design of the controller is based on modal decomposition of the gyroscopic system. This modal decoupling procedure leads to a control mechanism implemented in modular form, which represents a distinct computational advantage over the control of the coupled system. Design procedures are demonstrated for two types of control algorithms, linear and nonlinear. The first represents classical linear feedback approach and the second represents an application of on-off control, both types made feasible by the modal decomposition scheme.

Meirovitch, L.↗
NASA NTRS1979

Control of large flexible space structures using pole placement design techniques

A design approach via the pole placement techniques for the class of large flexible space structures is developed. The numerical problems in pole placement algorithm, arising from large dimension systems and the extremely low frequency eigenvalues which occur in large space structure models are examined. It shows these numerical difficulties may be overcome by properly selecting the sensor/actuator locations and introducing a frequency scaling scheme. The concepts of this paper are illustrated by some numerical studies on the linear feedback control design of a representative large spacecraft consisting of a small rigid core with ten radial booms (five booms 1000 ft long and five shorter booms 700 ft long) lying in a plane.

Wu, Y. W.↗
NASA NTRS1983

On vibration control of tethered satellite systems

The general dynamics of a shuttle supported tethered subsatellite system taking into account the longitudinal and three dimensional transverse vibrations is considered. It is noted that control of inherently unstable dynamics during retrieval of the subsatellite can be carried out by letting the rate of change length depend on the state variables in an appropriate manner. Control laws using linear feedback of inplane state variables and nonlinear feedback of out-of-plane state variables are proposed.

Xu, D. M.↗
NASA NTRS1983

Control of the constrained planar simple inverted pendulum

Control of a constrained planar inverted pendulum by eigenstructure assignment is considered. Linear feedback is used to stabilize and decouple the system in such a way that specified subspaces of the state space are invariant for the closed-loop system. The effectiveness of the feedback law is tested by digital computer simulation. Pre-compensation by an inverse plant is used to improve performance.

Bavarian, B.↗
NASA NTRS1985

A mathematical formulation of the Scole control problem, part 1

A mathematical formulation of the SCOLE control problem in terms of a continuous model described by partial differential equations with delta functions on the boundary is presented along with three techniques of solution. The abstract wave equation approach leads immediately to a linear feedback law that can ensure (strong) stability. The boundary control approach yields an explicit solution, albeit in a simple case.

Balakrishnan, A. V.↗
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.↗
NASA NTRS1986

A simple algorithm for computing canonical forms

It is well known that all linear time-invariant controllable systems can be transformed to Brunovsky canonical form by a transformation consisting only of coordinate changes and linear feedback. However, the actual procedures for doing this have tended to be overly complex. The technique introduced here is envisioned as an on-line procedure and is inspired by George Meyer's tangent model for nonlinear systems. The process utilizes Meyer's block triangular form as an intermedicate step in going to Brunovsky form. The method also involves orthogonal matrices, thus eliminating the need for the computation of matrix inverses. In addition, the Kronecker indices can be computed as a by-product of this transformation so it is necessary to know them in advance.

Ford, H.↗
NASA NTRS1985

Evaluation of performance characteristics for a space antenna system subjected to stochastic disturbances

Control system synthesis for a large space antenna system is investigated based on stochastic linear optimal control techniques and the minimization of a quadratic Gaussian performance index. Parametric studies indicate that suitable combinations of plant and sensor noise characteristics, and state weighting matrices, can be found to meet the mission RMS pointing requirements. Using a combination of the Kalman filter and linear feedback, an optimal control law for the finite element model of the Hoop/Column structural system without damping is obtained. Removing the hoop-mounted actuator resulted in an increase in the RMS errors, an increased control effort, and an increase in the least damped modal time constant. Removing the hoop-mounted sensor resulted in an RMS error increase and estimator performance degradation, with less system RMS performance degradation than noted for removal of the hoop-mounted actuator.

Ananthakrishnan, S.↗
NASA NTRS1985

Single step optimization strategies for constrained retargeting maneuvers

The present consideration of recent advancements in the nonlinear guidance of spacecraft, using feedback linearization and decoupling to generate exact nominal commands, gives attention to the correction of saturation effects and oscillation prevention in saturated operating regimes. In the case of spacecraft maneuvered by momentum-transfer devices, real time command generation is possible by means of pointwise minimization of the sum of the squares of the norms of the 'next state error' for the equivalent system and the linear system input. It is also possible to track a nominal trajectory, such as a critically damped harmonic oscillator response, by minimizing the square of the norm of the error between the actual and the tracked states.

Dwyer, T. A. W., III↗
NASA NTRS1988

Large planar maneuvers for articulated flexible manipulators

An articulated flexible manipulator carried on a translational cart is maneuvered by an active controller to perform certain position control tasks. The nonlinear dynamics of the articulated flexible manipulator are derived and a transformation matrix is formulated to localize the nonlinearities within the inertia matrix. Then a feedback linearization scheme is introduced to linearize the dynamic equations for controller design. Through a pole placement technique, a robust controller design is obtained by properly assigning a set of closed-loop desired eigenvalues to meet performance requirements. Numerical simulations for the articulated flexible manipulators are given to demonstrate the feasibility and effectiveness of the proposed position control algorithms.

Huang, Jen-Kuang↗
NASA NTRS1988

Adaptive guidance for an aero-assisted boost vehicle

An adaptive guidance system incorporating dynamic pressure constraint is studied for a single stage to low earth orbit (LEO) aero-assist booster with thrust gimbal angle as the control variable. To derive an adaptive guidance law, cubic spline functions are used to represent the ascent profile. The booster flight to LEO is divided into initial and terminal phases. In the initial phase, the ascent profile is continuously updated to maximize the performance of the boost vehicle enroute. A linear feedback control is used in the terminal phase to guide the aero-assisted booster onto the desired LEO. The computer simulation of the vehicle dynamics considers a rotating spherical earth, inverse square (Newtonian) gravity field and an exponential model for the earth's atmospheric density. This adaptive guidance algorithm is capable of handling large deviations in both atmospheric conditions and modeling uncertainties, while ensuring maximum booster performance.

Pamadi, Bandu N.↗
NASA NTRS1988

Coprime factorizations in stable linear systems

A block-diagonal linear (not necessarily time-invariant) map P with a right-coprime factorization ND-1 (or a left-coprime factorization D-1N) is considered. It is shown that the individual blocks in P have right-coprime factorizations (left-coprime factorizations, respectively) if and only if the denominator map D has a special block-triangular structure. This condition is applied to the stable linear feedback system S(P1,P2).

Desoer, Charles A.↗