Abstract
Mars has been an active planet for space exploration since the 1960s. The future Mars missions, such as searching for life, could be accomplished by the technique up to date, but the Martian aerobots allow a longer range and a lower altitude compared with rovers and orbiters, respectively. Hyperion is an autonomous fixed-wing solar-electrical vertical take-off and landing aerobot proposed based on the previous work to investigate the Isidis Planitia region. The proposed aerobot is a coaxial tiltrotor design with two auxiliary rotors at the wing-tips. This thesis focuses on two topics: aerodynamic design of the coaxial tiltrotor system and robust flight control for transition phases. Due to the limited solar flux on Mars, it is necessary to improve the efficiency of the coaxial tiltrotor system. The vortex based theory has the highest computational efficiency (high computational precision and low computational cost). Two models, the Prescribed Wake Model (PWM) and the Free Wake Model (FWM), are used in this work. The PWM is used in the optimization process; while the FWM is used to provide data to determine the empirical equations and validate the PWM results. The optimal coaxial rotors for both hover and cruise have significant improvement (approximately 10% less power) compared with the baseline design. The final coaxial tiltrotor is obtained by a weighted average of the two optima in hover and cruise conditions. The performance of the proposed coaxial tiltrotor is very close to that of the optima for both hovering and cruise conditions. The flight control system is another important aspect for such a special Martian aerobot, especially for the transition and the conversion between hover and cruise. It is known that the aerodynamic property for an aerobot is difficult to predict, so the aerodynamic coefficients used in this work follow the usual practice that an uncertainty (+-20%) is imposed for the aerodynamic terms. In this thesis, a robust controller based on u synthesis and Divide and Conquer gain scheduling method is proposed to design the controller for transition flight. A 6-degree-of-freedom simulation with aerodynamic uncertainty validates the feasibility and the robustness of the proposed controller. The simulation shows that the transition can be accomplished within 150s. Although the altitude in the simulation shows a acceptable steady state error (+-1m). The other state variables are robustly stablized during the transition flight.