Application of Multidisciplinary Design Optimization to the Development of an Unmanned Suborbital Spaceplane by Industry-Government-Academia Collaboration

Development of suborbital spaceplanes with rocket engines is in progress under the industry-government-academia collaboration with the initiative of a Tokyo University of Science's start-up, SPACE WALKER Inc. This paper presents the progress and the last result of the preliminary design of an unmanned suborbital spaceplane called FuJin, from April 2019 to September 2021. FuJin performs vertical take-off and horizontal landing, and its mission is to transport 100 kg payload to the apogee altitude of 120 km. In the preliminary design of FuJin, multidisciplinary design optimization (MDO) techniques have been utilized. Detail design analysis models for propulsion, structure, and electrical/mechanical equipment are developed and updated by industries, and the integrated optimization of vehicle design and trajectory design are conducted using MDO. It makes it possible to obtain the design solution with the minimum lift-off mass while taking complicated design constraints into account. For this purpose, MDO methods and tools that are suited to the industrial application are newly implemented. During the preliminary design, system-level design has been revised 24 times according to the updates of the design analysis models. Especially, the vehicle size and aerodynamic planform have changed considerably. Since the structure mass estimated at the beginning of the preliminary design was too small, the first design had the total length of 9.3 m and the lift-off mass of 7.8 t, while the last design has the total length of 13.4 m and the lift-off mass of 18.6 t. Because the estimated position of the center of mass has moved backward as the preliminary design proceeded, the aerodynamic planform has been modified in order to satisfy the longitudinal trim and static stability throughout the trajectory.