# Effect of Structural Materials on Monopropellant Thruster Propulsion Performance in Micro Scale
## 2 Materials for Microthruster Fabrication
The thruster was manufactured with a commercial LTCC tape and tested using the monopropellant hydroxylammonium nitrate (HAN), and a DC voltage potential was applied across electrodes in order to initiate decomposition of the propellant, generating approximately 150 mN of thrust for a pulse operation. Despite the occasional structural failure (in the case of rapid ignition), the feasibility of the material in a monopropellant microthruster fabrication was demonstrated. [PERSON] et al. [25] utilized high-temperature co-fired ceramic (HTCC) zirconia tape to fabricate a microthruster, the material of which tends to endure a higher working temperature than that of the LTCC (thelatter softening at a temperature of approximately 800 \({}^{\circ}\)C). Although the yttria-stabilized zirconia (YSZ)-based microthruster was not tested and evaluated with regard to propulsion performance, the established fabrication process was determined to be successful, and its accuracy was evaluated favorably. [PERSON] et al. (2018) also utilized HTCC to manufacture a hydrogen peroxide monopropellant microthruster with an integrated heater and temperature sensors. Despite its limited interest in thruster propulsion performance, the study proved the feasibility of HTCC for hydrogen peroxide monopropellant microthruster fabrication, and it reported that the material was able to endure the working temperature. [PERSON] and [PERSON] (2018); [PERSON] and [PERSON] (2018), reporting on a 50 mN class microthruster manufactured using glass in the photolithography process and tested with 90 wt% hydrogen peroxide as the monopropellant and platinum as the catalyst for propellant decomposition, established the advantages of the insulating effects of glass for the successful decomposition of the propellant. As discussed and summarized in Table 1, various materials have been applied to different micro-propulsion system designs and fabrications, validating their feasibility in the manufacturing process. However, these studies mainly focused on the MEMS fabrication process itself, as well as the compatibility of certain materials with the manufacture of a microthruster, as opposed to the characteristics of the materials themselves and their effects on propulsion performance in the micro scale. The effects of microthruster structural materials on propulsion performance are of particular importance in light of the excessive heat loss experienced by miniaturized propulsion systems, which is due to the large surface-to-volume ratio in the micro scale, and the tendency for greater heat loss as the systems are further downsized. In addition, the monopropellant thruster, which is one of the chemical propulsion systems most conducive to miniaturization, requires a catalyst in its microchamber to effect propellant decomposition, itself affected by the surrounding temperatures, which are generally degraded by the excessive heat loss in the micro scale. Therefore, despite the various studies which have been conducted on the development of micro-propulsion systems using different fabrication processes and materials, further studies are essential to investigate their effects on heat loss and corresponding propulsion performance degradation.