sentences:  SE&I also managed the mass of the vehicle and developed the trajectory and the guidance, navigation, and control algorithms used for vehicle flight.To complete these tasks, wind tunnel testing and computational fluid dynamics (CFD) were used to investigate forces acting on the vehicle in various phases of flight, including lift-off, ascent, stage separation and descent.Once the basic design was understood SE&I provided structural analyses for the system to assure the rocket would behave properly once it was integrated.