Modeling and Control of a Balloon Borne Stabilized Platform

Abstract

A balloon borne stabilized platform has been developed for a remotely operated altitude-azimuth pointing of a millimeter wave telescope system. A modeling and controller design of the azimuth point system of the platform is presented. Simulation results show that the system is capable of continuous operation with pointing rms to better than 0.01 deg. Ground testing results show continuous operation with pointing rms to better than 0.02 deg; while results of the first flight from the National Scientific Balloon Facility (NSBF) at Palestine, Texas show pointing rms better than 0.02 deg.

Modeling and stability of balloon-borne gondolas with coupled pendulum-torsion dynamics

“…The azimuth pointing control of balloon-borne gondolas is most often designed solely with a model of the torsion of the flight train [7][8][9][10][11][12][13][14][15]. However, in presence of a coupling between the gondola's azimuth and the pendulum oscillations of the system, the azimuth control can excite and even destabilize the pendulum modes.…”

“…Two types of dynamics are generally distinguished in the modeling of balloon systems. About the vertical axis, the torsion of the flight chain is traditionally modeled as a mass-spring system [7][8][9][10][11][12][13][14][15]. Although the stiffness is generally experimentally determined by system identification, which requires to deploy the whole system and process in-flight data, the bifilar pendulum model allows to analytically derive the stiffness of balloon flight chains [16,17].…”

Modeling of stratospheric balloons and robust line-of-sight pointing control

“…The earliest dynamical models of stratospheric balloonborne systems are found in 1975 in a technical report from NASA [10] motivated by the attitude determination for the LACATE experiment, and developed further by the same authors [11][12][13]. About the vertical axis, the torsion of the flight chain is traditionally modeled as a mass-spring system [14][15][16][17][18][19][20][21][22]. Although the stiffness is generally experimentally determined by system identification, which requires to deploy the whole system and process in-flight data, the bi-filar pendulum model allows predicting analytically the stiffness of balloon flight chains [23,24].…”

“…To the authors knowledge, there exists no general model-based methodology for controller synthesis in the literature, and, more critically, experimental ground-based setups are not representative of the dynamics of the fully deployed system in flight (which cannot be obtained in laboratory due to the dimensions of the system), whereas flight experience proves that the lineof-sight control is essentially limited by the rejection of the natural pendulum-like modes of the flight chain [2], excited by wind disturbance. Although some more advanced control techniques were investigated (pole assignment [2,15], LQR synthesis [14], adaptive control [16], sliding mode control [21,45], Lyapunov stability theory [26]), they provide very few insight on the achievable performance. The third contribution of this paper is a general methodology to address the line-of-sight pointing control of an optical instrument onboard a stratospheric balloon as a robust structured H 2 ∕H ∞ problem.…”