Analysis of Momentum Exchange in Spacecraft Attitude Dynamics and Control, National Science Foundation, 1999-2001. The principal goal of this research is to develop a complete understanding of the dynamics and control of momentum exchange in spacecraft. While these problems have received significant attention in the literature, many of the results have been developed for linearized equations of motion. Recent global analysis of nonlinear equations of motion has led to significant new results, and suggests new lines of research for previously intractable problems. The equations of motion describing these systems are expressed in noncanonical Hamiltonian form, with several perturbing torques considered. One objective is to characterize completely the relative equilibrium motions of spacecraft with internal energy dissipation, with special attention to those asymptotically stable equilibria corresponding to a stationary platform. This will be applied to the nonlinear control of rotational maneuvers, including optimal control maneuvers and sub-optimal stationary-platform maneuvers. Stationary-platform maneuvers are based on a simple feedback law, and have the useful property that the platform angular velocities remain small throughout any maneuver. Global analysis of other problems, such as escape from resonance trap states, resonance capture avoidance, dual-spin turn, and flat spin recovery will complete the basic understanding of momentum exchange in gyrostats. This will require extensions of standard tools in perturbation and bifurcation theory, and will yield results with definite applications to spacecraft design. Additional investigations will analyze the effects of various realistic perturbations, where improved understanding will lead to improved designs of attitude control systems. A unique element of the research is the investigation of the historical development of momentum exchange in spacecraft. We will characterize the relationship between the academic developments as reported in research literature and the developments that have taken place in the satellite industry. This effort will identify the critical events in the development of this technology, including both elegant mathematical results and catastrophic attitude control system failures.

Virginia Tech Ionospheric Scintillation Measurement Mission, Universities Space Research Associates, FY99-00. This project supports the interaction of Virginia Tech students with students at Utah State University and The University of Washington, on the design, manufacture, test, integration, deployment and operation of the Ionosphere Observation Nanosatellite Formation (ION-F). See http://www.aoe.vt.edu/~hokiesat for further details.

Virginia Tech Ionospheric Scintillation Measurement Mission, AFOSR/DARPA, FY99-00. This project is part of Air Force Research Laboratory's University Nanosatellite Program. Students at Virginia Tech will design, build, and fly a 10-kg "nanosat" that will be launched on the space shuttle in 2001. See http://www.aoe.vt.edu/~hokiesat for further details.

Modeling and Simulation of Formation Flying, NASA Goddard Space Flight Center, FY99. We are investigating the dynamics and control problems associated with flying a formation of remote sensing satellites. Both orbital and attitude dynamics and control are considered, with emphasis on attitude dynamics and control. Since orbit dynamics is simpler and is usually more closely related to mission design, it is covered first. Attitude dynamics and control depends on the orbit and on the mission performance requirements. For a formation of free-flying telescopes, the orbit dynamics problems are associated with the fact that any particular noncoplanar configuration of satellites cannot be maintained indefinitely without station-keeping. Therefore, the formation must be designed to meet basic mission requirements, and the station-keeping control must be designed to provide the formation stability required for the mission. Ideally, a formation would minimize the amount of station-keeping required, and the optics post-processing system would maximize the accuracy of the images obtained. We will carefully evaluate the tradeoffs between altitude, inclination, relative spacing, and number of telescopes in order to maximize performance while minimizing the station-keeping costs. This will include the effects of Earth oblateness (J2), which may provide some capability to maintain the formation and reduce station-keeping costs.

Rotational Dynamics and Control of Magnetic Bearing Systems, Oak Ridge Associated Universities, FY99.

Formations of Free-Flying Gyrostat Telescopes, AFOSR, FY98-00.

Spacecraft Simulator, ASPIRES Grant, FY98.

Using Satellites in Teaching Undergraduate Astrodynamics, Center for Excellence in Undergraduate Teaching Grant, FY98.

Satellite Tracking Laboratory, SCHEV, FY98.

Reorientation of Flexible Space Structures Using Momentum Exchange Devices. Air Force Office of Scientific Research, FY97 (at AFIT).

Satellite Applications Laboratory. Air Education and Training Command, FY97. Co-PI with Professor D. Goldizen (at AFIT).

Rotational Dynamics Laboratory. Air Education and Training Command, FY97 (at AFIT).

Integrated Power and Attitude Control of Spacecraft with Electro-Mechanical Flywheel Batteries. Phillips Laboratory, FY97–98 (at AFIT).

Techniques and Applications of Multivariable Nonlinear Control. Air Force Office of Scientific Research, FY96–98. Co-PI with Professor D. B. Ridgley (at AFIT).

Asteroid Mitigation and Spacecraft Maneuverability. Air Force Space Command, FY96. Joint research project with Professor I. Michael Ross of the Naval Postgraduate School (at AFIT).

Steady Motions of Rigid Satellites in a Central Gravitational Field. Air Force Office of Scientific Research, FY93 (at AFIT).