Design and optimization of RBCC powered suborbital reusable launch vehicle

In response to a demand for fast access to near space, a horizontal take-off and horizontal landing Suborbital Reusable Launch Vehicle (SRLV) concept powered by Rocket Based Combined Cycle (RBCC) engine is proposed in this research. This SRLV is designed to deliver a 20,000 kg payload to an altitude of 50km and a velocity of Mach 8, and to be able to fly back to the launch site. Compared with classical rocket launch vehicles and cruise vehicles, this vehicle applies unconventional configuration, flight path and propulsion working mode, and interactions between disciplines are very distinct. As there is scarce knowledge and data to refer to, we are faced with challenges in conceptual design. In this article, a two-phase design methodology is developed for RBCC powered vehicles. In the first phase, a sequential design flow with several design steps is utilized to find a feasible or near-feasible baseline. The methods used in this phase include: 1) a simplified trajectory for weight and sizing, 2) a multi-point optimization for aerodynamic shape design over a wide range of speeds, 3)a multi-point optimization for RBCC engine design to meet requirements of all working modes, 4) an integrated analysis process for aerodynamic/propulsion performance calculation, 5) a gauss-pseudo spectral based trajectory optimization to find the optimal flight path, 6) a structural design and sizing method, and 7) an automatic thermal protection system concept selection and sizing method. Also, considering the features of the vehicle, interactions between these steps are considered. With these methods and several iterations between them, the baseline of vehicle concept is created. In the second phase, Multi-Disciplinary Optimization (MDO) is applied to improve baseline for a feasible and better design. During this phase, optimization problem of SRLV, including design variables, constraints, and objectives, is created. The disciplinary high-fidelity models of and couplings between them are set up. By applying an asymmetric MDO architecture, the synthesis MDO model is integrated. Response Surface Method and Sequential Quadratic Programming algorithm are used in this architecture to find a closure and optimal solution. The application results from presented SRLV show that for a given launch task, the optimal design with all constraints satisfied can be found by this two-phase design methodology. We also find that this methodology is almost knowledge independent and suitable to conceptual design of unconventional vehicle like RBCC powered SRLV.