# Effect of Structural Materials on Monopropellant Thruster Propulsion Performance in Micro Scale
## 4 Results and Discussion
### Chamber Pressure and Thrust
Figure 15 indicates that the propellants with higher weight percentage (i.e., higher enthalpy) lead to more degradation with regard to the two normalized performance parameters in all material cases considered except the adiabatic one and that they are more sensitive to the variation of structural materials. Based on the result, it is predicted that other monopropellant alternatives, such as ammonium dinitramide (ADN) or hydroxylammonium nitrate (HAN)-based propellant with higher decomposition temperature, are likely to have higher sensitivity on materials with a greater difference in propulsion performance between materials and more degradation of propulsion performance in actual cases compared to the adiabatic case. The effect of the materials on microthruster performance clarifies how much performance degradation is expected depending on the fabrication materials used for a micropropulsion system with different propellant enthalpies. The performance degradation characteristics reported through this analysis were obtained focusing on the effect of materials on propulsion performance and are limited in terms of a simulation model without considering the case of insufficient catalyst reactivity under the working temperature lowered by the thermal energy loss. However, as can be found in relevant studies [13; 16; 41], which reported experimentally tested results of a 50 mN class thruster with an amount of thrust generation in the range of approximately 28 mN [16] to 48 mN [13], there is an influence of the catalyst on propellant decomposition efficiency affected by operating temperature in microthrusters. Thus, further degradation of propulsion performance is anticipated to occur due to the catalyst effect in thrusters in the micro scale, in addition to the structural material effect reported in this study. This is expected to provide a useful \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Parameters** & **wt\%** & **Adiabatic** & **Glass** & **LTCC** & **Stainless Steel** & **HTCC** & **Silicon** & **Copper** \\ \hline \multirow{3}{*}{Thrust (mN)} & 95\% & 82.12 & 78.81 & 77.86 & 76.90 & 76.79 & 76.51 & 76.48 \\  & 90\% & 77.16 & 74.19 & 73.35 & 72.51 & 72.41 & 72.17 & 72.14 \\  & 85\% & 72.03 & 69.42 & 68.70 & 67.96 & 67.88 & 67.66 & 67.64 \\ \hline \multirow{3}{*}{Heat transfer coefficient \# (W m\({}^{-2}\) K\({}^{-1}\))} & 95\% & N/A & 281.91 & 292.31 & 311.41 & 313.63 & 319.52 & 320.31 \\  & 90\% & N/A & 261.80 & 273.48 & 292.40 & 294.52 & 300.14 & 300.89 \\  & 85\% & N/A & 246.13 & 258.56 & 276.86 & 278.86 & 284.10 & 284.80 \\ \hline \multirow{3}{*}{Temperature outside surface * (K)} & 95\% & N/A & 553.27 & 622.81 & 691.45 & 698.73 & 718.04 & 720.64 \\  & 90\% & N/A & 510.00 & 567.04 & 623.92 & 629.96 & 645.98 & 648.13 \\  & 85\% & N/A & 469.23 & 514.94 & 560.95 & 565.84 & 578.82 & 580.56 \\ \hline \multirow{3}{*}{Temperature nozzle \# (K)} & 95\% & 1144.00 & 1042.00 & 1022.7 & 1007.2 & 1005.8 & 1002.1 & 1001.6 \\  & 90\% & 1021.40 & 932.83 & 916.71 & 903.84 & 902.65 & 899.63 & 899.23 \\  & 85\% & 898.69 & 825.96 & 812.96 & 802.58 & 801.62 & 799.19 & 798.87 \\ \hline \multirow{3}{*}{Temperature nozzle \# (K)} & 95\% & 1026.6 & 951.48 & 931.41 & 911.73 & 909.66 & 904.2 & 903.47 \\  & 90\% & 908.55 & 845.64 & 829.01 & 812.52 & 810.78 & 806.19 & 805.57 \\  & 85\% & 795.75 & 744.52 & 731.06 & 717.56 & 716.14 & 712.4 & 711.9 \\ \hline \multirow{3}{*}{Temperature nozzle \# (K)} & 95\% & 831.55 & 757.99 & 738.37 & 719.09 & 717.01 & 711.60 & 710.89 \\  & 90\% & 730.29 & 669.17 & 653.08 & 636.82 & 635.12 & 630.61 & 629.98 \\ \cline{1-1}  & 85\% & 634.83 & 585.48 & 572.50 & 559.32 & 557.93 & 554.33 & 553.83 \\ \hline \hline \end{tabular}  
* area averaged/* theoretical decomposition temperature as a reference.  
\end{table} 
Table 5: Summary of the simulation results in regard to the different materials and propellant weight percentages.