Optimal reconfigurable allocation of a multi-engine cluster for a reusable launch vehicle
Creators: name:  R. MURATA 
name:   L. THIOULOUSE 
name:   J. MARZAT 
name:   H. PIET-LAHANIER 
name:   M. GALEOTTA 
name:   F. FARAGO 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: REUSABLE SYSTEMS
FLIGHT PHYSICS
DYNAMICS

description: The launcher market is highly competitive and complete or partial recovery of rockets appears to be a promising way to reduce operating costs. The development of a Reusable Launch Vehicle (RLV) using a toss-back boost to return to the launch site implies new needs for thrust modulation and control, closed-loop dynamics and engine monitoring. In order to handle these problematics, multi-engine propulsion bays are currently designed in Europe for the next generation of launchers [1]. This work is part of the PIC CNES/ONERA on Reusable Launch Vehicles (RLV). The system considered here consists of a cluster of multiple liquid-propellant rocket engines (LPRE). Each engine disposes of a 2-DOF thrust vector control (TVC) and of a thrust throttling capability. The problem addressed is the coordination of the individual set-points in terms of thrust module and gimbal angles, so as to produce the overall force and torque reference requested by the guidance and control at launcher level. This can be formulated as a constrained optimal control allocation problem for an over-actuated mechanical system [2]. Additionally, to meet fault tolerance requirements and improve the reliability of the propulsion bay, this control allocation module should take into account faults such as the complete loss of an engine, a decrease of thrust efficiency and the stuck gimballing axes. These faults would be identified by a dedicated Health Monitoring System (HMS), out of the scope of this work. The objective of the present paper is to formalize the allocation problem under constraints (minimum and maximum thrust levels, maximum gimbal angle) so as to design a generic control allocation module and validate its behaviour on different propulsive clusters and scenarios. Among several candidate optimization techniques tested (pseudo-inverse, simplex, interior point) [3], an interior point algorithm with an adequate formulation of the optimization problem turns out to be the most efficient strategy which also respects the constraints of the allocation problem. The generic test case addressed considers the simultaneous allocation of thrust module and gimballing angles for each engine according to an objective function that minimizes TVC actuation and the allocation error under physical constraints. To illustrate the performance of the proposed method and provide recommendations for the design of future multi-engine propulsion bays, several simulation results are presented for different cluster configurations (namely 3, 7 and 9 engines) for two test cases (with and without TVC actuation), under various nominal and faulty conditions. Engine and TVC transfer functions are also taken into account to show the overall dynamical performance of the reconfigurable control allocation module. References [1] S. Colas, S. Le Gonidec, P. Saunois, M. Ganet, A. Remy, V. Leboeuf, A point of view about the control of a reusable engine cluster. 2019. In: 8th European Conference for Aerospace Sciences (EUCASS). [2] T. A. Johansen, T. I. Fossen, Control allocation - a survey. 2013. Automatica (49(5), 1087-1103). [3] E. Walter, Numerical methods and optimization. 2014. New York, Springer.