Software design of 6DOF guidance approximations in 3DOF ascent simulations

Methods are being developed for approximating 6DOF (degrees of freedom) motion characteristics in an operational 3DOF trajectory simulation. The optimizable 3DOF and the nonoptimizable 6DOF simulations are used for launch planning and operations for a current U.S. launch vehicle program. A previous paper discussed the derivation and impact on the 3DOF in terms of vehicle attitude and angle of attack time histories. This paper continues by developing the methodology within the simulation and optimization software framework. It must take into account both the frequency and the sequencing of calls to various FORTRAN subroutines that model vehicle flight mechanics. These calls and the routines must be planned so as not to violate assumptions upon which the nonlinear programming algorithms used to shape the trajectory are based. Discussion is included on the steps that must be taken to sufficiently simplify the 6DOF booster guidance scheme. In order to do this, a careful review is made of how the trajectory is described and propagated. This description is developed wtihin the context of the various required reference frames and the vehicle attitudes specified with respect to those frames.