An observer-based attitude and nutation control and flexible dynamic analysis for the NASA Magnetospheric Multiscale Mission

Current research with the NASA Goddard Space Flight Center (GSFC) involves the dynamic modeling and control of the NASA Magnetospheric Multiscale (MMS) Mission, a. Solar-Terrestrial Probe mission to study Earth\u27s magnetosphere. Four observer-based attitude and nutrition controllers are designed and evaluated to determine the most effective feedback control system as it applies to MMS. Also, a dynamic analysis of each of the four identical satellites\u27 two Axial Double Probe (ADP) booms is performed to provide an understanding of flexible boom dynamics. The Finite Element method is used in evaluating boom modes of vibration for confirmation of NASA GSFC theoretical analysis and use in flexible model development. The dynamic transient and modal extraction technique are investigated for vibration analysis of constrained and unconstrained bodies. A fully flexible boom and rigid spacecraft model is also developed for vibrational analysis under steady-state rotation and thruster loads. Results indicate, however, the need for future research in numerical analysis of propagating systems through finite element methods and in the stability of the observer-based control system. Linear and nonlinear observers are developed through simulations to estimate satellite attitude and angular body rates without the use of rate sensors. Control systems are then developed assuming perfect state measurements. Euler angles are used to describe satellite attitude in this research. Finally, linear and nonlinear (Sliding Mode Control) techniques are implemented in conjunction with the nonlinear observers to complete the observer-based control system. The results of this research show that, of the methods analyzed, both the Extended Kalman Filter and Sliding Mode Observer implemented with Sliding Mode Control yield the most satisfactory performance. These observer-based control systems both meet NASA design requirements while reducing thruster control effort and reducing the effects of measurement noise and spacecraft uncertainties/disturbances. More simulations, however, are needed to verify performance of the proposed observer-based control system over all possible ranges of operation

Dynamics and control of advanced space vehicles, volume 1

The following studies are reported: (1) Modal analyses of elastic continua for Liapunov stability analysis of flexible spacecraft; (2) development of general purpose simulation equations for arbitrary spacecraft; (3) evaluation of alternative mathematical models for elastic components of spacecraft; and (4) examination of the influence of vehicle flexibility on spacecraft attitude control system performance

The pointing errors of geosynchronous satellites

A study of the correlation between cloud motion and wind field was initiated. Cloud heights and displacements were being obtained from a ceilometer and movie pictures, while winds were measured from pilot balloon observations on a near-simultaneous basis. Cloud motion vectors were obtained from time-lapse cloud pictures, using the WINDCO program, for 27, 28 July, 1969, in the Atlantic. The relationship between observed features of cloud clusters and the ambient wind field derived from cloud trajectories on a wide range of space and time scales is discussed

Control of free-flying space robot manipulator systems

New control techniques for self contained, autonomous free flying space robots were developed and tested experimentally. Free flying robots are envisioned as a key element of any successful long term presence in space. These robots must be capable of performing the assembly, maintenance, and inspection, and repair tasks that currently require human extravehicular activity (EVA). A set of research projects were developed and carried out using lab models of satellite robots and a flexible manipulator. The second generation space robot models use air cushion vehicle (ACV) technology to simulate in 2-D the drag free, zero g conditions of space. The current work is divided into 5 major projects: Global Navigation and Control of a Free Floating Robot, Cooperative Manipulation from a Free Flying Robot, Multiple Robot Cooperation, Thrusterless Robotic Locomotion, and Dynamic Payload Manipulation. These projects are examined in detail

AFWAL space control technology program

An overview of space oriented control technology programs which are applicable to flexible large space structures is presented. The spacecraft control activity is interdisciplinary with activities in structures, structural dynamics and control brought together. The large flexible structures to be controlled have many physical factors that influence the final controllability of the vehicle. Factors are studied such as rigidity of both structural elements and joints, damping inherent in both material as well as discrete dampers located throughout the structure, and the bandwidth of both sensors and actuators used to sense motion and control it. Descriptions of programs both in-house and contracted are given