2017.B.3.2. Development of green propellant microthrusters at KAIST
Jeongmoo Huh (1)
Juwon Kim (1)
Sejin Kwon (1)
- Korea Advanced Institute of Science and Technology (KAIST), South Korea
Microthruster, Green propellant, Photosensitive glass
This work reports green propellant liquid micro scale propulsion systems at KAIST. Using photolithography procedure, several monopropellant microthrusters were fabricated for approximately 50 mN class thrust generation. To achieve sufficient propellant decomposition and to overcome excessive heat loss stemmed from large surface to volume ratio of micro scale device, a low thermally conductive material was considered in this work. Photosensitive glass with lower thermal conductivity than that of generally used MEMS fabrication material; silicon, was used for the microthruster fabrication. Five glass layers with each component of the thruster composed the microthruster. In addition, to increase decomposition efficiency of a propellant by a catalyst, a catalyst was made with large reacting surface area and robustness in high temperature and pressure condition. As an active material of the catalyst, platinum was chosen and coated on an alumina support. The catalyst was directly inserted into the microthruster chamber and then total glass layers were integrated. We tried to test the microthruster using three different propellants; pure hydrogen peroxide, hydrogen peroxide blended with a small amount of ethanol, and Ammonium dinitramide(ADN). The fabricated photosensitive glass microthruster successfully operated using pure and blended hydrogen peroxide, and performance comparison between two microthrusters showed improved specific impulse and more stable average thrust generation by propellant blending. These test results presented not only feasibility of use of the photosensitive glass as the fabrication material for a microthruster with more insulating effect, but also good performance of platinum/alumina catalyst for sufficient propellant decomposition. For the microthruster using ADN propellant, however, experimental thrust test result showed burned out catalyst and cracked glass structure indicating the need of catalyst and structure improvement in terms of robustness to thermal stress. Enhancement of catalyst durability in high temperature and structure with the cooling channel is currently considered for performance improvement. Although several things are needed to be improved, liquid microthrusters were fabricated using photosensitive glass MEMS process, and performances were successfully experimentally tested using green propellants, the advantage of which is safety and low development cost without expensive safety gear. The result is expected to further liquid micro propulsion technologies safely at low cost for cube satellite applications including orbit transfer, attitude control and drag compensation.
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