Mixture-Ratio Control to Improve Hydrogen-Fuel Rocket Performance

The rocket equation of motion, in the absence of gravitational and aerodynamic forces, is integrated by considering the propellant mixture ratio as the problem control variable. The theory of optimal control is applied to obtain the control law, which maximizes the payload for an assigned velocity increment when the tank mass is assumed to be proportional to the propellant volume. The control strategy, which minimizes the rocket dry mass for assigned payload and velocity increment, is also investigated. For a low-velocity increment, the mixture-ratio range required by the optimal control is not ample, and the improvement with respect to the constant mixture-ratio operation is small; however, large differences in the mean mixture ratio are present, depending on the performance index. The optimal control law is almost independent of the considered index for the most demanding missions, whereas the mixture ratio exhibits a large variation: in this case the control of the mixture ratio can significantly improve rocket performance with respect to the constant mixture-ratio operation. (Author)