Engineering topics

Chichester, F. D.

Publications and source records attributed to Chichester, F. D..

13 records

NASA NTRS1984

Modular design attitude control system

A sequence of single axismodels and a series of reduced state linear observers of minimum order are used to reconstruct inaccessible variables pertaining to the modular attitude control of a rigid body flexible suspension model of a flexible spacecraft. The single axis models consist of two, three, four, and five rigid bodies, each interconnected by a flexible shaft passing through the mass centers of the bodies. Modal damping is added to each model. Reduced state linear observers are developed for synthesizing the inaccessible modal state variables for each modal model.

Chichester, F. D.↗

NASA NTRS1984

Modular design attitude control system

The problem of applying modular attitude control to a rigid body-flexible suspension model of a flexible spacecraft with some state variables inaccessible was addressed by developing a sequence of single axis models and generating a series of reduced state linear observers of minimum order to reconstruct those scalar state variables that were inaccessible. The specific single axis models treated consisted of two, three and four rigid bodies, respectively, interconnected by a flexible shaft passing through the mass centers of the bodies. Reduced state linear observers of all orders up to one less than the total number of scalar state variables were generated for each of the three single axis models cited.

Chichester, F. D.↗

NASA NTRS1983

Modular design attitude control system

Application of modular control techniques to the attitude control of a prototype flexible spacecraft and a prototype flexible space platform was further developed by determining numerical values for the physical parameters of a four body approximation of the MSFC/hybrid deployable truss incorporated in the space platform model, generating sensitivity coefficients for the model of the flexible spacecraft, evaluating the changes in the digital computer simulation of the flexible spacecraft resulting from the addition of another rigid body to the model and comparing attitude control effectiveness with actuators on more than one rigid body of the model with that for the case in which the actuators were restricted to one body.

Chichester, F. D.↗

NASA NTRS1983

Modular design attitude control system

The problem of applying modular attitude control to a rigid body - flexible suspension model of a flexible spacecraft with some state variables inaccessible was addressed by developing a sequence of single axis models and generating a series of reduced state linear observers of minimum order to reconstruct those scalar variables that were inaccessible. The specific single axis models treated consisted of two, three and four rigid bodies, respectively, interconnected by a flexible shaft passing through the mass centers of the bodies. Reduced state linear observers of all orders up to one less than the total number of scalar state variables were generated for each of the three single axis models cited.

Chichester, F. D.↗

NASA NTRS1983

Comparing attitude control effectiveness for actuators on two bodies of a six body model of a flexible spacecraft with that for actuators restricted to a single body

A ten rigid body model of a prototype flexible space platform was approximated by a six body model to facilitate comparison of attitude control effectiveness for actuators on two bodies with control effectiveness for actuators restricted to a single body of the same model. Actuators and sensors were found to be required on two of the six bodies for effective attitude control.

Chichester, F. D.↗

NASA NTRS1983

Developing sensitivity coefficients for a state variable model of a flexible spacecraft with modular attitude control

The numerical value for the sensitivity coefficient of each scalar state variable with respect to each parameter of a five body model of the rotational dynamics of a flexible spacecraft with modular attitude control is generated. The maximum magnitudes of these sensitivity coefficients are arranged in descending order in one table while the final time (steady state) values of these sensitivity coefficients are arranged in order of descending magnitude in a second table.

Chichester, F. D.↗

NASA NTRS1982

Modular design attitude control system

A hybrid multilevel linear quadratic regulator (ML-LQR) approach was developed and applied to the attitude control of models of the rotational dynamics of a prototype flexible spacecraft and of a typical space platform. Three axis rigid body flexible suspension models were developed for both the spacecraft and the space platform utilizing augmented body methods. Models of the spacecraft with hybrid ML-LQR attitude control and with LQR attitude control were simulated and their response with the two different types of control were compared.

Chichester, F. D.↗

NASA NTRS1982

Modular attitude control of a large space platform

The modular attitude control of a large space platform is studied using a three axis five body model of a flexible spacecraft. Three degree of freedom hinges are considered. A three axis four body model of a truss and a three axis ten body model of a space platform are presented. A state variable rotational dynamics model and a multilevel state variable model are shown. A decomposed performance index and decomposed Hamiltonian are also presented. A subproblem hierarchy for hybrid multilevel LQR attitude control of a three axis model is described.

Chichester, F. D.↗

NASA NTRS1982

Approximating a finite element model of a hybrid deployable truss by a discrete mass model

The NASTRAN finite element model of the MSFC/hybrid deployable truss is approximated by a model consisting of four bodies serially connected by a spring hinge suspension. The truss is decomposed into four serially connected modules determining the total mass and rotational inertias for a rigid body with its mass center on the axis of the truss for each module. A five-body cantilever truss model is developed along with an undamped form of this model. Spring coefficient values are generated to match eigenvalues of the latter model with those of the NASTRAN model. Damping coefficients are then determined that provide n percent of critical damping for the model.

Chichester, F. D.↗

NASA NTRS1981

A multilevel control approach for a modular structured space platform

A three axis mathematical representation of a modular assembled space platform consisting of interconnected discrete masses, including a deployable truss module, was derived for digital computer simulation. The platform attitude control system as developed to provide multilevel control utilizing the Gauss-Seidel second level formulation along with an extended form of linear quadratic regulator techniques. The objectives of the multilevel control are to decouple the space platform's spatial axes and to accommodate the modification of the platform's configuration for each of the decoupled axes.

Chichester, F. D.↗

NASA NTRS1981

Application of Gauss-Seidel multilevel control to a single axis torsional model

An approach to the application of multilevel control techniques for large space structures is presented. Gauss-Seidel second level controls and an extension of standard linear quadratic regulator techniques are applied to a model consisting of a flexible space vehicle comprising three rigid bodies rotating about a common axis. The method incorporates second order derivatives with respect to time, entailing the use of a two level hierarchy of subsystems. Gauss-Seidel second level control formulations were chosen to avoid the necessity of having as many controls as constraints or using gradient techniques in the choice of the Hamiltonian. The modular nature of the resulting control system allows applications for spacecraft with larger numbers of modules.

Chichester, F. D.↗

NASA NTRS1979

Multilevel modeling of the space construction base

A mathematical model representing a flexible space vehicle in terms of interconnected discrete masses is recast into hierarchical form to facilitate the application of multilevel control techniques. The model's state equations are temporarily decoupled by utilization of a set of coordination equations. A hierarchical form of the model is constructed with the set of coordination equations at the top of the hierarchy and the set of decoupled scalar state equations in the bottom level.

Chichester, F. D.↗

NASA NTRS1979

Application of hybrid coordinate modeling and multilevel control techniques to a single axis torsional model

Hybrid coordinate modeling and multilevel control techniques are applied to a prototype flexible vehicle. The original hybrid coordinate model developed for this vehicle is expressed in terms of one rigid body coordinate and two modal vibration coordinates. Multilevel control techniques of decomposition, coordination and construction of the subproblem hierarchy are applied to this model.

Chichester, F. D.↗