Six degrees-of-freedom atmospheric entry characteristics of the NASA sponsored commercial experiment transporter (COMET) recovery vehicle using the program to optimize simulated trajectories (POST)

The purpose of this thesis to to conduct an analysis on the flight dynamic characteristics of COMmercial Experiment Transporter's (COMET) Recovery Vehicle (RV), with no controls. The COMET Service Module will not be considered in this work. The three and the six, translational and rotational, degrees-of-freedom atmospheric entry characteristics are numerically computed using the Program to Optimize Simulated Trajectories (POST). There are two versions of POST three and six degrees-of-freedom, 3D POST & 6D POST, respectively. POST has been implemented using the fourth order Runge-Kutta numerical integration algorithm for both degrees-of-freedom. An oblate spinning earth is considered. A 1976 U.S. Standard Atmosphere is used. All the aerodynamic coefficients used are input as functions of the local angle. It is found that the nominal conditions of entry, particularly the roll rate, greatly affects the behavior of the vehicle at lower altitudes. Oscillatory numerical solutions are discussed. Angular, axial and transverse accelerations are considered. Perturbing the roll rates changes the sensed acceleration on the body. There is a slight increase of the accelerations due to increased roll rates, which is due to increased centrifugal acceleration. Convergence/Divergence of oscillation envelopes is also examined. This vehicle, as all blunt nosed vehicles, such as the Mercury capsule, has been determined to have a divergence of the oscillation envelope after maximum dynamic pressure is reached. This occurs due to the fact that the drag coefficient of these vehicles is relatively larger than the lift coefficient. The roll rate greatly affects the touch down point of the vehicle. The downrange error of the touchdown increases by about thirty percent as the roll rate is increased from two and a half to five revolutions per minute. The percentage of increase is virtually the same from five to seven and a half revolutions per minute. The heating rate calculations are determined by use of the three degrees-of-freedom version of POST.