A survey of automatic control methods for liquid-propellant rocket engines

Abstract

The main purpose of this survey paper is to review the field of convergence between the liquid-propellant rocketpropulsion and automatic-control disciplines. A comprehensive collection of academic works and some industrial developments are summarised and discussed, making the link to the current context of launcher reusability. The main control problem in liquid-propellant rocket engines (LPRE), the target of this survey, generally consists in tracking set-points in combustion-chamber pressure and mixture ratio, their main operating quantities. This goal is attained via the adjustment of flow-control valves while complying with operating constraints. Each aspect of control systems, ranging from modelling to the actual control techniques, is reviewed and subsequently related to the rest of aspects. The comparison of the different approaches points to the general use of linearised models about concrete operating points for deriving steady-state controllers, which in most cases are of PID type. Other more sophisticated approaches present in the literature, incorporating some nonlinear, hybrid or robust techniques, improve certain aspects of performance and robustness. Nevertheless, no fully nonlinear or hybrid frameworks, which may allow the control of a wider throttling domain, have been published. In addition, control during the thermally and structurally demanding transient phases is usually in open loop, and hence with low correction margins. This sort of control enhancements, probably together with more sophisticated monitoring architectures, would serve to extend the life of LPRE, a significant factor in their reusability. Therefore, this survey intends to draw a path for the future control design trends which will certainly be more suitable for reusable LPRE.

Arresting-Cable System for Robust Terminal Landing of Reusable Rockets

“…Thus, quantities of velocity were normalized by gl 0 p , of acceleration by g, and of force by m r g. Then, the equation of motion [Eq. (13)] could be reformulated into another dimensionless form as…”

“…Now, based on well-developed high-precision guidance technologies, the guidance errors have been diminished from kilometers to meters with nearly minimum fuel consumption [10][11][12]. In the second terminallanding step, the current vertical-recovery technique requires not only advanced engines that are capable of multiple restarts and thrust modulation within a large range [13][14][15] but also an accurate control system to prevent the rocket from crashing [16,17]. Moreover, the high heat flux on the base plate [18] and the reconfigured aerodynamic characteristics [17] during the touchdown phase require thermal protection for the structure and accurate landing [19].…”

A Reinforcement Learning Approach for Transient Control of Liquid Rocket Engines

“…Closed-loop control is at most used near steady operating conditions to maintain a desired combustion chamber pressure and mixture ratio [7]. For an extensive overview of the different studied control strategies, which include PI, PID, LQR and robust control methods, the reader is referred to the survey by Pérez-Roca et al [8]. The resulting lower deviations of the controlled variables decrease the amount of extra propellant to be carried, which in turn increases the payload capacity of the launch vehicle.…”

A Two-Parameter Corresponding States Method for Calculating the Steady-State Evaporation Rate of C2–C9 n-Alkane Droplets in Air for Elevated Pressures and Temperatures

“…Methane is the most promising liquid-propellant in the space industry (Pérez-Roca et al 2019). N-butane is popular in spark-ignition engines to improve mixture formation (Jung et al 2017).…”