  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.
