Peter M. Bainum, Ph.D.
Distinguished Professor of Aerospace Engineering

Phone: 202-806-6612
Email: [email protected]

Research Topics
Structural/control optimization of large space structures; control of flexible expendable launch vehicles; formation flying of orbiting satellites

Summary of Recent Research
This work deals with the simultaneous structural/control optimization of a large space structure (LSS) in low Earth orbit (LEO) subject to the gravity-gradient. The objective from the structural viewpoint is to attain a low weight structure satisfying constraints on the first natural frequency, on the side constraints, and on the damping from the control. Simultaneously the optimal control is to be reached for the structure with the same constraints. It is also desired to confirm the possibility to optimize such a structure by taking the damping factor as input from the control designer. The effect of the coupling between the elastic vibration and the pitch attitude motionon the transient response and on the control effort is analyzed. The control system objectives are the elastic vibration suppression and the attitude control (pitch motion). The LSS orbit is assumed to be circular and the motion is confined on the orbital plane. The NEWSUMT-A and the OPT software are integrated with the ORACLS control package to solve the simultaneous optimization problem. NEWSUMT-A stands for a new sequence of unconstrained minimization techniques to reach the structural optimization. While this software implements the indirect optimization approach, the OPT program solves the structural optimization by using the Genearlized Reduced Gradient (GRG) methods. ORACLS computational package implements the Linear Quadratic Regulator to optimize the control cost function. One executive program has been developed and implemented to integrate the three software packages to obtain the integrated structural/control optimization. The result shows relevant reduction in the structural weight with respect to the initial given structure. From the control side the control performance and the damping factor is better than that for the initial given structure. The result shows also that in this case it is possible for the control designer to give some input in the structural design.

A strategy for maintaining separation distances between four satellites in a coplanar elliptical orbiting constellation is developed. A possible scientific application of such a system would be in measuring the curl of the Earth's magnetic field by taking simultaneous measurements along the elliptical orbit. The strategy involves maneuvers which would cause small shifts in the direction of the four semi-major axes. With this approach for Keplerian type orbits, the separation distance between adjacent satellites remains within a few percent of the nominal separation distance. Simulations based on MATLAB and the BG-14 orbital propagator (including various perturbations) show that most of the control energy would be used to compensate for these non-Keplerian perturbations.

Based on a general review of the dynamics and control as well as relevant references for launch vehicle systems, a simplified mathematical model suitable for subsequent control design has been established. The model considers the attitude, lateral transverse motions coupled with flexible bending modes, the sensor and actuator dynamics and the wind gust loads. There are three gyros in the system, one is for rotational orientation the other two are for rotational rates. According to requirement of the grant sponsor the problem of sensor redundancy is studied. It has been suggested that an accelerometer collocated with the orientation gyro be added to the system as an additional sensor for redundancy. The effect of the accelerometer on the system dynamics and stability is also studied, especially in the situation where one or two gyros fail.

Recent Publications
Ericsson-Jackson, Aprille J., Bainum, Peter M., and Xing, Guangqian, "Application of a Singular Value Decomposition Method to Digitally Controlled Large Orbiting Platform," Journal of Guidance, Control, and Dynamics, Vol. 21, No. 4, July-August 1998, pp. 551-557.

Tan, Zhaozhi and Bainum, Peter M., "Study of Sensor Redundancy and Effect of Accelerometer Feedback for Control of Flexible Expendable Launch Vehicles," accepted for publication in Special Theme issue: Space Systems, Phil. Trans. A, Royal Society, 1999.

Fonseca, Ijar M., Bainum, Peter M., and Lourencao, Paulo, T.M., "Structural and Control Optimization of a Space Structure Subject to the Gravity-Gradient Torque," 49th International Astronautical Congress, Melbourne, Australia, Sept. 28 - Oct 2, 1998, Paper No. IAF98-I.2.03.

Tan, Zhaozhi, Bainum, Peter M., and Strong, Avaine, "A Strategy for Maintaining Distance Between Satellites in an Orbiting Constellation," AAS/AIAA Space Flight Mechanics Meeting, Breckenridge, Colorado, Feb. 7-10, 1999, Paper No. AAS 99-125.

Bainum, Peter M., Fonseca, Ijar M., and Laurencao, Paulo, T.M., "Structural/Control Optimization of a Large Low Orbit Structure," Proc. 6th Pan American Congress of Applied Mechanics and the 8th International Conference on Dynamic Problems, Applied Mechanics in the Americas, Vol. 8, Ed. D, Pamplona et al, Riode Janeiro, Branl, Jan. 4-8, 1999, pp. 1127-1130.