山田 和彦

One of the most important goals in aerospace engineering applications is the creation of new “flyable” systems. In a flight demonstration using the sounding rocket S-520-34, we show the first successful operation of a bipropellant cylindrical rotating detonation engine using liquid ethanol and liquid nitrous oxide, Detonation Engine System 2 (DES2), in a space environment. From the pressure and temperature histories, the combustion was finished before all propellants were consumed because nitrogen was supplied earlier than the ideal depletion time due to spin stabilization of the sounding rocket. Therefore, the combustion pressure decreased from the nitrogen-supply start time. The short-time Fourier transform result indicated that the deflagration mode, two-wave mode, and single-wave mode occurred in sequence. This was attributed to the locally lower liquid temperatures, wall temperature, and mixture ratio at ignition near the wall, where the rotating detonation wave propagated. A comparison of the filling mass and consumption indicated that the mass flow rate estimated using control surface theory reflects an actual phenomenon. As for the propulsive performance, the experimental characteristic exhaust velocity was almost the same as the ideal value. Moreover, a specific impulse efficiency of more than 90% was achieved throughout the rotating detonation engine operation.

A thin aeroshell capsule can decelerate from high altitude, which reduces aerodynamic heating, and can land without a parachute due to its low ballistic coefficient during entry, descent, and landing. However, the characteristics of its attitude are unclear, leading to capsule design issues. The Rubber Balloon Experiment for Reentry Capsule with Thin Aeroshell was conducted to confirm the stable flight of a capsule with a thin blunt nose at low speeds and demonstrate a low-cost balloon experiment with few constraints on the balloon launch. The capsule, with a mass of 1.56 kg and a diameter of 0.8 m, was released at an altitude of 25 km using a rubber balloon. The capsule experienced low-attitude oscillation and landed without becoming unstable. In balance with the air drag, the flowfield during flight had a maximum Mach number of 0.15 and Reynolds number of [Formula: see text], which is similar to the flowfield around an actual deep space sample return capsule descending at low speeds. The translational oscillation in the drag direction and rotational oscillations in pitch and yaw were dominant. The experiment suggested that the capsule of deep-space sample return capsule has the potential to undertake a dynamically stable flight in the low-speed region.

As a new atmospheric-entry technology, the research and development of atmospheric-entry vehicles with flexible aeroshells has been rapidly expanding. A lightweight and large-area flexible aeroshell enables a low-ballistic coefficient of flight and an efficient aerodynamic deceleration, thereby reducing aerodynamic heating and communication blackouts. Aerodynamic forces deform flexible aeroshells, altering their aerodynamic characteristics. However, the manner in which the attitude characteristics change when the aeroshell undergoes significant shape deformation is not well understood. In this study, the attitude and aerodynamic characteristics of a flexible aeroshell were clarified using wind tunnel tests at a given angle of attack and corresponding fluid–structure interaction (FSI) analysis. The FSI analysis method is based on a partitioned coupling method for large-scale parallel computers that use open-source software. The FSI analytical model reasonably explained the aeroshell deformation and aerodynamic coefficient behavior, and its validity was confirmed by wind tunnel experiments. The shape deformation of the flexible aeroshell weakened its restoring motion, thus exhibiting attitude instability compared with those prior to deformation.