Citation: Cha, J.; de Oliveira, É.J.
Performance Comparison of Control
Strategies for a Variable-Thrust
Solid-Propellant Rocket Motor.
Aerospace 2022, 9, 325. https://
doi.org/10.3390/aerospace9060325
Academic Editors: Mikhail
Ovchinnikov and Dmitry Roldugin
Received: 20 May 2022
Accepted: 11 June 2022
Published: 16 June 2022
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Article
Performance Comparison of Control Strategies for a
Variable-Thrust Solid-Propellant Rocket Motor
Jihyoung Cha
1,
* and Élcio Jeronimo de Oliveira
1,2
1
Department of Computer Science, Electrical and Space Engineering, Luleå University of Technology,
RYMDCAMPUS 1, 98192 Kiruna, Sweden; elcioejo@innospc.com.br
2
INNOSPACE Brazil, Av. São João 2375, São José dos Campos 12242-000, Brazil
* Correspondence: jihyoung.cha@ltu.se
Abstract:
This paper deals with a performance comparison of the control algorithm for a variable-
thrust solid-propellant rocket motor (VTSRM). To do this, we develop a simulation model of a
VTSRM considering characteristic changes in the combustor and design control systems for pressure
and thrust. We use three types of control algorithms for the pressure control: classical PID control,
feedback linearization control, and fuzzy PID control, and two control algorithms for thrust control:
classical PID control and fuzzy PID control. Finally, we compare the performance of each control
system through a numerical simulation using step responses. Through this work, we check that
feedback linearization is better in pressure control, and fuzzy PID control is more appropriate in
thrust control. Especially using fuzzy PID control, we can get fast settling with a small undershoot
even if the system is a nonminimum phase system.
Keywords:
variable-thrust solid-propellant rocket motor; pressure control; thrust control; nonminimum
phase system; performance comparison
1. Introduction
Solid-propellant rocket motors (SRMs) have simple structures and are suitable for
long-term storage compared to other types of propellant systems, so they have been used
for various applications [
1
–
5
]. However, once the specifications of an SRM, including
propellant and nozzle throat area, are determined, the thrust level of the system is generally
fixed and hard to control [
1
]. In the recent two or three decades, to overcome the weakness
of the system, the studies related to a variable-thrust solid-propellant rocket motor (VTSRM)
using the special nozzle with a pintle valve have been progressed [
6
,
7
]. The pintle nozzle is
a special nozzle with a movable pintle to change the nozzle throat area. It causes chamber
pressure and nozzle exit pressure to be adjusted, so the thrust control becomes available by
the effects, as shown in Figure 1.
Furthermore, these days, using these characteristics, the ramjet or scramjet system,
called dual-mode ramjet (DMRJ) or solid-fuel rocket scramjet (SFRSCRJ), has been devel-
oped and studied as in Figure 2 [
8
–
11
]. The fuel-rich combustion gas, generated from the
solid propellant system, is controlled by the pintle, and it makes variable thrust in the ram
combustor. Therefore, the characteristics of the system drive are one of several challenges
in the DMRJ, and SFRSCRJ is the accurate control of combustion gas flow rate using a
control valve such as a pintle valve.
However, although pressure or thrust will be controlled by a pintle accurately and
straightforwardly, there is a limited position to move the pintle, as shown in Figure 3. If a
pintle moves closer to the nozzle throat pass over the limited position, a severe accident
can occur, such as an explosion, because of the unbalance of pressure and exit mass flow
rate. Therefore, the pressure and thrust control by appropriate pintle position with stability
is the main subject for single-nozzle VTSRPM and thrust distribution by pintle position for
the multi-nozzle with stable pressure. For the design control system, a dynamic simulation
model of a VTSRM is required, and modeled as a nonlinear differential equation with
Aerospace 2022, 9, 325. https://doi.org/10.3390/aerospace9060325 https://www.mdpi.com/journal/aerospace
