Accession Number : ADA291803

Title :   Spacecraft Attitude Control System Performance Using Pulse-Width Pulse-Frequency Modulated Thrusters.

Descriptive Note : Master's thesis,

Corporate Author : NAVAL POSTGRADUATE SCHOOL MONTEREY CA

Personal Author(s) : McClelland, Robert S.

PDF Url : ADA291803

Report Date : MAR 1994

Pagination or Media Count : 101

Abstract : Many current satellites employ on-off thrusters to accomplish attitude control tasks which may include initial acquisition, rotational maneuvers, and on-orbit stabilization. This work shows that the use of pulse-width pulse-frequency (PWPF)-modulated thrusters provides several important advantages over conventional bang- bang thruster control methods, including less thruster activity and closer-to-linear actuation. The PWPF modulator is implemented in simulations using the Matrix/System build software package. Simulations assuming a rigid spacecraft are first performed to compare the performance of the PWPF-modulated thrust controller with that of conventional bang-bang and time-optimal bang-bang controllers. The discussion is then extended to the case of a spacecraft with structural flexibility, as is encountered quite often in three-axis stabilized vehicles with large fold-out solar arrays. Simulations for comparison of the controllers are performed using the flexible spacecraft dynamics model. The control loop design in the presence of flexibility and possible interaction with the PWPF modulator nonlinearity are addressed. Using a describing function model of the modulator, stability margin with respect to the structural mode limit cycle is predicted. Simulations are then conducted to verify the predicted stability margin.

Descriptors :   *ATTITUDE CONTROL SYSTEMS, *THRUSTERS, *SATELLITE ATTITUDE, *PULSE FREQUENCY MODULATION, STABILIZATION, COMPUTER PROGRAMS, ORBITS, STABILITY, SPACECRAFT, ACQUISITION, MODELS, DYNAMICS, STRUCTURAL PROPERTIES, COMPARISON, THESES, CYCLES, NONLINEAR SYSTEMS, LIMITATIONS, ARTIFICIAL SATELLITES, MANEUVERS, LOOPS, ROTATION, RIGIDITY, MODULATORS, FLEXIBLE STRUCTURES.

Subject Categories : Radiofrequency Wave Propagation
      Astronautics
      Spacecraft Trajectories and Reentry

Distribution Statement : APPROVED FOR PUBLIC RELEASE