Ongoing Research
Observation of the metal combustion for micropropulsion
Small propulsion vehicles are especially required to be safe for launch to the ISS and release from the ISS. The use of safe propellants and mechanisms is a prerequisite for small propulsion vehicles. For this reason, chemical propulsion using chemical reactions is rarely used. We are searching for a propulsion system, such as a metal-water hybrid rocket, that is very safe when loaded, but can generate a large amount of propulsive force when used. Metal flames can reach temperatures as high as 3000 K, but the boiling point of metal oxide is above that, and "condensation and combustion products" (CCPs) are quickly formed.
Facility effect on micronozzle performance
In ground tests, a high vacuum of about one-millionth of an atmospheric pressure is created to simulate space. However, this vacuum is not equivalent to the actual space environment. This pressure difference affects the performance of the micro-thrust nozzle, and a gap appears between the ground test and space operation. This research aims to quantitatively clarify this gap and to construct a correction system that links ground tests and space performance. This research is conducted using experimental and numerical methods.
Facility effect on ion thruster
Ion thrusters, a type of electric propulsion system, are characterized by high specific impulse of 1000-10000 s among electric propulsion systems. Facility effects are also an issue for ion thrusters, including (1) CEX ion formation due to high background pressure, (2) changes in the ion plume neutralization process due to 0 V ground test equipment, and (3) backspatter from the ejected ion beam. We will simulate the operation of ion thrusters on the ground to understand the phenomena occurring on the ground and to quantify the differences between the ground and space. This research is conducted in collaboration with the University of Illinois, USA.
Past Research
Rarefied gas flow of saturated water vapor inside micronozzles
Water is attracting attention as a propellant for ultra-small spacecraft. Water is also expected to outperform conventional propellants in smaller sizes because of its safety and its low-pressure, liquid nature, which reduces the structural mass required to carry it onboard. Water stored in liquid form is released in a gaseous state after evaporation, but because of its low vapor pressure (~1 kPa) and near boiling point, the supersonic flow at the nozzle does not follow an idealized prediction equation. Experimental thrust measurements and one-dimensional CFD calculations, including condensation, will help to understand the phenomena caused by supersonic flow and to predict and improve the performance of water thrusters.
Water droplet vaporization under microgravity condition
As mentioned above, water is not only attracting attention as a propellant for micro spacecraft, but its affinity with human life makes it a promising propellant for future manned space activities. In addition to gas jet propulsion, its use in various chemical and electrical propulsion applications is also being considered. On the other hand, the microgravity environment of space in particular affects water evaporation and its impact on flow control, especially the ability to properly separate vapor from liquid, is critical. Droplets that are suddenly subjected to a low-pressure environment evaporate through a form of nucleate boiling and are dispersed in the evaporation chamber. In a microgravity environment, where surface tension is apparent, the dispersal of droplets has the effect of increasing the contact between the liquid and the walls of the evaporation chamber, thereby accelerating evaporation.
