An attitude controller for a variable-pitch Mars quadcopter with parameter scheduling under varying atmospheric densities

With the continued advancement of Mars exploration, the successful flights of the Ingenuity Mars Helicopter have demonstrated the feasibility of rotorcraft and established aerial exploration as an emerging approach in Mars missions. However, the extremely low atmospheric density on Mars, which fluctuates significantly with seasonal and diurnal temperature variations, affects the dynamic characteristics of flight control model and poses challenges for attitude controller design. To address the issues associated with low and variable atmospheric density, this paper investigates the attitude control of a variable-pitch Mars quadcopter. A flight control model for the quadcopter is first established, followed by the experimental identification of hover operating points and model parameters under different atmospheric densities. Based on the model obtained after a series of processing steps such as linearization and time delay approximation, a hyperbolic tangent integral sliding-mode (TISMC) attitude controller with parameter scheduling is then designed. Flight experiments conducted within a Mars Atmosphere Simulator under varying density conditions show that the TISMC controller achieves average values of 0.01208 for attitude angle fluctuation standard deviation, 1.824^∘ for steady-state error, and 0.2974 s for delay time. These results represent reductions of approximately 47.8%, 40.2%, and 10.6%, respectively, compared with a conventional PID controller. The results demonstrate that combining a variable-pitch configuration with a parameter-scheduled sliding-mode strategy effectively addresses the challenges posed by the thin and time-varying Martian atmosphere, offering a viable control solution for future Mars quadcopter missions.