The six degrees of freedom modeling and simulation of launch vehicles including sensitivity analysis

For the purpose of this thesis, a six degrees of freedom trajectory model was developed and verified for launch vehicle systems and an already operated launcher Minotaur-I was simulated with this tool. Moreover, the same tool was also used for sensitivity analysis for several important parameters of the vehicle. Launch vehicles or carrier rockets are used to transport one or more payloads from Earth's surface to space and launch vehicles are used for both commercial or military satellites, meteorological observation, and experimental researches. From the beginning of the space race, a variety of launch vehicle systems have been developed and operated to reach space, accomplish the assigned mission and gain global prestige. A six degrees of freedom equations of motion model using translational and angular motions was developed with its library functions such as coordinate systems transformation, mathematical operations, Euler and quaternions transformation, atmosphere and gravity models. US Standard Atmosphere Model 1976 and EGM2008 Gravity Model were implemented to use with equations of motion. Nine different check cases data for a simple sphere, brick and two-stage rocket verified by NASA were used for verification of the developed tool. The verification process included gravitational, translational, rotational equations of motion, inertial coupling, integration method of differential equations, rotation of the Earth, ellipsoidal Earth, Coriolis effects, staging and entire atmosphere verification steps, respectively. In addition to verified library functions and equations of motion with rotating oblate Earth, an example mission of Minotaur-I launch vehicle was simulated. For the modeling of Minotaur-I, CATIA for mass and inertia model and Missile DATCOM for the aerodynamic model were used and the desired parameters were achieved at the end of the simulation. The sensitivity analysis of some essential parameters for flight path and performance of launch vehicles were fulfilled after the successful simulation. The analysis parameters involved gross lift-off weight of the vehicle, specific impulse of each stage, pitch-over maneuver initial and final times, each stage ignition time and pitch-over maneuver angle. The analysis showed that the specific impulse of the first stage is the most dominant parameter among the whole variables. Overall results demonstrated that even small modifications in launch vehicle parameters play a substantial role in launcher trajectory, performance and reliability.