Modelling and control of a balloon-borne stabilized platform

This dissertation is concerned with the development of a balloon borne stabilized platform for the detection of anisotropy in the Cosmic Background Padiation (CBR). The control and design objective is to develop an accurate altitude-azimuth pointing and stabilizing system to keep the targeted celestial source within the beam size of the antenna and detector system. Since the beam has an angular size of 0.33 to 0.75 degree, the pointing error rms should be better than 0.10 degree both in azimuth and elevation.; The experimental setup is described and descriptions of the major hardware used in the experiment are given.; A mathematical model of the azimuth pointing system is derived. Using pole placement technique, the model is used as a basis to structure and to design a proportional{dollar}sb{lcub}-{rcub}{dollar}integral{dollar}sb{lcub}-{rcub}{dollar}derivative (PID) control with constant desaturation of flywheel angular velocity. Model reference adaptive control (MRAC) with constant desaturation of flywheel angular velocity is also developed. Simulation results indicate that both controllers are capable of continuous azimuth pointing with error rms better than 0.01 degree.; The development of software programs to coordinate the experiment is discussed. Software development includes the implementation of computer based PID control and MRAC both with constant desaturation of flywheel velocity, stiction and calibration compensations for the elevation pointing system, strategies for trajectory generations, gyro recovery during flight, data scheduling and other flight operations.; Extensive ground test results verified that the software programs are adequate and functional. Results also indicate that the system is capable of azimuth and elevation pointing with error rms better than 0.02 degree and 0.04 degree, respectively.; The first flight launched from the National Scientific Balloon Facility (NSBF) at Palestine, Texas showed that the hardware functioned properly during the course of the experiment. Tracking results indicate that the azimuth pointing is better than 0.02 degree rms, while elevation pointing is better than 0.04 degree rms. The flywheel angular velocity was also maintained below the saturation limit to provide continuous azimuth pointing.; Problems encountered during the flight are discussed. Recommendations for improvement of the balloon borne stabilized platform system for future experiments are presented.