Rate control system algorithm developed in state space for models with parameter uncertainties

Adilson Jesus Teixeira

doi:10.5028/jatm.2011.03033511

Abstract

researching in weightlessness above the atmosphere needs a payload to carry the experiments. To achieve the weightlessness, the payload uses a rate control system (RCS) in order to reduce the centripetal acceleration within the payload. The rate control system normally has actuators that supply a constant force when they are turned on. The development of an algorithm control for this rate control system will be based on the minimum-time problem method in the state space to overcome the payload and actuators dynamics uncertainties of the parameters. This control algorithm uses the initial conditions of optimal trajectories to create intermediate points or to adjust existing points of a switching function. It associated with inequality constraint will form a decision function to turn on or off the actuators. This decision function, for linear time-invariant systems in state space, needs only to test the payload state variables instead of spent effort in solving differential equations and it will be tuned in real time to the payload dynamic. It will be shown, through simulations, the results obtained for some cases of parameters uncertainties that the rate control system algorithm reduced the payload centripetal acceleration below µg level and keep this way with no limit cycle.

Highlights

The microgravity environment to perform experiments can be obtained in several ways
Rate control system algorithm developed in state space for models with parameter uncertainties
1 0 -1 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 get the desired low gravity level, the rate control system (RCS) control algorithm created one segment for the switching function, according to the error measured during the transition B and generated another command to the negative actuator to drive the payload state vector to the origin of the state space

Summary

INTRODUCTION

The microgravity environment to perform experiments can be obtained in several ways. One of them uses a sounding rocket that carries a payload out of atmosphere influence and the experiments are performed during the payload ballistic phase. It was observed that the final conditions of the switching function for the RCS algorithm needed to be changed a little bit and had to to be added some inequality constraints (Bryson et al, 1997) to compensate the simulation step and to reduce the limit cycle amplitude, when angular velocity of the payload mathematical model is close to zero. These inequality constraints and the switching function compound a decision function that will generate the conditions to turn on or off the actuator. The control law must use the following tests, according to each area: 1. Red Area: Actuator ON p < Sf (p') U p < -pMax (6)

White Area

Findings

CONCLUSION