丸 祐介

ISAS/JAXA has been conducting research and development on the reusable sounding rocket with air-breathing engines called New Sounding Rocket. Its propulsion system is Air Turbo Rocket for Innovative Unmanned Mission (ATRIUM) engine, which combines an air-turbo engine and a rocket engine. A three-dimensional supersonic inlet for the rocket was designed for Mach 2.0 based on a Busemann inlet. The flow field and the performance of the designed inlet were investigated at the design and off-design points by conducting wind tunnel tests and CFD simulations. At the design point with a freestream Mach number of 2.0, a shock wave formed near the inlet entrance induced flow separation and reduced the inlet performance. Compared to the theoretical values in the critical state, the mass capture ratio and the total pressure recovery were reduced by about 0.2 and up to 0.41, respectively. As for the off-design characteristics, at Mach number of 1.5, the mass capture ratio was significantly reduced due to larger spillage flow by the shock wave formed near the entrance of the inlet. At Mach number of 2.5, the total pressure recovery became smaller because the total pressure loss due to the terminal shock wave was larger than that at the design point. It was concluded that the flow path of the designed inlet would need to be modified to improve its performance, considering the influence of the boundary layer.

On July 11th, 2019, the Hayabusa2 spacecraft achieved its second touchdown on the asteroid Ryugu with a 0.6 m accuracy. The landing was accomplished based on the newly implemented Pin-Point Touchdown (PPTD) method. It was extended from the former Touchdown (TD) method established by the Hayabusa spacecraft. When changing the point of view, two TDs of Hayabusa2 are regarded as successful autonomous rendezvous-dockings (RVDs) against the artificial landmark in deep space more than 15 minutes of light time from the Earth. This paper proposes the Deep Space Orbital Transfer Vehicle (DS-OTV) concept inspired and driven by Hayabusa2 technology to economically support various future deep space missions. The DS-OTV usually stays in a parking orbit at the boundary of the Earth system and possesses autonomous RVD functionality against the visiting deep space probes. The OTV provides the following services: (1) refueling of chemical bipropellant to the probe enabling it to transfer into the interplanetary trajectory by itself, (2) insertion of the visiting probe into the high-C3 Earth free-return orbit. This paper introduces the background and the concept of the OTV, and the simulation-based feasibility analysis results applying the Hayabusa2's PPTD method to the DS-OTV mission.

When a spacecraft fires its thrusters near the surface of a celestial body, objects on the surface of the body are scattered in the vertical direction and adhere to the cameras and ranging instruments mounted on the spacecraft, degrading their performance. In order to establish a future spacecraft design theory that is less sensitive to the scattering of surface objects, we first investigate the scattering factors and scattering tendencies of surface objects. We predict that celestial surface objects are scattered according to the wall angle of the crater created by the thruster plume. The relationship between the crater shape and the object dispersal angle is not fully understood. Mechanisms of crater formation include viscous erosion, which creates craters with a small wall angle, and bearing capacity failure, which creates craters with a large wall angle. Here, we experimentally clarify the transition point between the two crater formation mechanisms when the thruster plume penetrates soil with various shear strength values. We find that the objects disperse along the crater wall for both mechanisms. Based on the results, we examine measures for preventing the spacecraft from being hit by scattered surface objects.