Experimental investigations of hydrogen peroxide monopropellant thrusters in order for design optimization were studied in this paper. The paper describes design methodologies of thruster in view of optimum sized thruster at a continuous mode and fast response characteristics at a pulse mode.
Firstly, a reactor sizing problem was focused. It should decompose the monopropellant completely for producing the design thrust. So, its size should be enough bulky for full decomposition of $H_2O_2$, but it is desirable to be minimized at the same time. Therefore, the critical size of a reactor was investigated. For this, the catalyst capacity (the ratio of reactant flowrate and reactor volume) was defined instead of mass flux because it can represent the catalyst reactivity directly. Mass flux did not denote the catalyst reactivity because it presents two-dimensional problem although it was generally used for designing the $H_2O_2$ thruster at literatures. The critical point of catalytic capacity was measured at a small scale test reactor, and then scale up process to 50 N was performed. The process was verified for performance evaluation at a scaled-up thruster.
Secondly, thrusters to be used at attitude control system require fast response times at pulse mode operations. It was assumed that a number of unknown parameters determine the pulse response times, so that parametric study was performed systematically. The possible factors to response times were classified into three groups - thruster component design (such as propellant tube, manifold, injector, catalyst volume, L/D ratio of a reactor, chamber volume), operating conditions (such as concentration of $H_2O_2$, feed pressure), active materials of catalysts. Seven different thrusters having 50 N were designed for these purposes, and the effect of each parameter on fast response was investigated experimentally.
Finally, design procedure of monopropellant was proposed at the end of this paper and additional considerations in designing process of the thruster were also discussed.
단일추진제 추력기의 설계 최적화를 실험적으로 연구하였다.
설계 추력을 만족시키기 위한 촉매 반응기 크기를 결정하는데 있어 기존 문헌에서 사용한 설계변수인 mass flux 대신 contact time 개념을 기반으로 하는 catalyst capacity라는 변수를 정의하고 이에 따른 추력기 사이징 방법을 제안하였다. 촉매대 압력 강하를 결정하는 주요 변수인 mass flux는 반응성능을 대변하지 못하므로 2차원 개념의 mass flux가 아닌 catalyst capacity를 반응기 부피를 결정하는 단계에서 설계 변수로 사용하였고 3차원 반응기 사이징 문제에 현실적으로 활용할 수 있었으며, mass flux는 정해진 반응기 부피에서 형상(L/D)을 결정하는데 적절하였다.
자세제어를 목적으로 하는 추력기는 빠른 펄스 응답 속도가 요구되지만, 매우 광범위한 요소들이 응답 속도에 영향을 미치게 되므로 체계적인 파라미터 연구를 통해 응답 특성을 고찰하였다. 응답 속도에 미치는 요인을 1) 추력기 설계 형상 인자, 2) 추력기 작동 조건, 3) 촉매의 특성으로 분류한 후, 세부 항목들이 응답 속도에 미치는 여부를 서로 다른 설계를 가지는 50 N 급 추력기 7기의 응답성 측정을 통해 각 요소들이 응답성에 미치는 정도를 확인하고 원인을 고찰함으로써 빠른 응답성을 위한 추력기 설계의 방향을 제시하였다.
