# An MPC Approach to Transient Control of Liquid-Propellant Rocket Engines

## TL;DR

This paper presents a nonlinear MPC-based control strategy for improving the transient start-up phase of liquid-propellant rocket engines, focusing on pressure, mixture ratios, and operational constraints.

## Contribution

It introduces a novel control approach combining nonlinear preprocessing with linear MPC for enhanced robustness and accuracy during engine start-up transients.

## Key findings

- Achieved precise end-state tracking of pressure and mixture ratios.
- Verified operational constraints during transient phases.
- Enhanced robustness through minimax optimization with perturbation scenarios.

## Abstract

The current context of launchers reusability requires the improvement of control algorithms for their liquid-propellant rocket engines. Their transient phases are generally still performed in open loop. In this paper, it is aimed at enhancing the control performance and robustness during the fully continuous phase of the start-up transient of a generic gas-generator cycle. The main control goals concern end-state tracking in terms of combustion-chamber pressure and chambers mixture ratios, as well as the verification of a set of hard operational constraints. A controller based on a nonlinear preprocessor and on linear MPC (Model-Predictive Control) has been synthesised, making use of nonlinear state-space models of the engine. The former generates the full-state reference to be tracked while the latter achieves the aforementioned goals with sufficient accuracy and verifying constraints for the required pressure levels. Robustness considerations are included in the MPC algorithm via an epigraph formulation of the minimax robust optimisation problem, where a finite set of perturbation scenarios is considered.