THEORETICAL MODELING AND COMPUTATIONAL SIMULATION OF ROBUST CONTROL FOR MARS AIRCRAFT

Abstract

The focus of this dissertation is the development of control system design algorithms for autonomous operation of an aircraft in the Martian atmosphere. This research will show theoretical modeling and computational simulation of robust control and gain scheduling for a prototype Mars aircraft. A few hundred meters above the surface of Mars, the air density is less than 1% of the density of the Earth's atmosphere at sea level. However, at about 33 km (110,000 ft) above the Earth, the air density is similar to that near the surface of Mars. Marsflyer II was designed to investigate these flight regimes: 33 km above the Earth and the actual Mars environment. The fuselage for the preliminary design was cylindrical with a length of 2.59 m (8.49 ft), the wing span was 3.98 m (13.09 ft). The total weight of the demonstrator aircraft was around 4.54 kg (10.02 lb). Aircraft design tools have been developed based on successful aircraft for the Earth`s atmosphere. However, above Mars an airborne robotic explorer would encounter low Reynolds Number flow phenomena combined with high Mach numbers, a region that is unknown for normal Earth aerodynamic applications. These flows are more complex than those occurring at high Reynolds numbers. The performance of airfoils at low Reynolds numbers is poorly understood and generally results in unfavorable aerodynamic characteristics. Design and simulation tools for the low Reynolds number Martian environment could be used to develop Unmanned Aerial Vehicles (UAV). In this study, a robust control method is used to analyze a prototype Mars aircraft. The purpose of this aircraft is to demonstrate stability, control, and performance within a simulated Mars environment. Due to uncertainty regarding the actual Martian environment, flexibility in the operation of the aircraft`s control system is important for successful performance. The stability and control derivatives of Marsflyer II were obtained by using the Advanced Aircraft Analysis (AAA) and Athena Vortex Lattice (AVL) programs. The uncertainty based on the stability and control derivatives of Marsflyer II was defined by running these programs. In addition, the comparisons of different trim conditions ascertain the need for gain scheduling about a linear controller system. An controller and H-infinity controller were applied to the design candidate aircraft controller systems. Simulations of the controller show that the H-infinity controller was more robust than the controller. The gain scheduled method was utilized for Marsflyer II inside a flight envelope using a linearized model from two selected trim points. The gain scheduling of Marsflyer II with both no gust and various gusts was achieved between these trim points. The controller derived from each trim point shows stable motion at the same trim condition. Both simulations of high altitude flight in the Earth`s atmosphere and the corresponding low altitude flight in the Martian atmosphere were completed using the robust controller for Marsflyer II. This research incorporates gain scheduling as well as robust control. The flight simulation of Marsflyer II was implemented within the Matlab/Simulink environment.