Flight dynamics (spacecraft)
Spacecraft flight dynamics is the science of space vehicle performance, stability, and control. It requires analysis of the six degrees of freedom of the vehicle's flight, which are similar to those of aircraft: translation in three dimensional axes; and its orientation about the vehicle's center of mass in these axes, known as pitch, roll and yaw, with respect to a defined frame of reference.Dynamics is the modeling of the changing position and orientation of a vehicle, in response to external forces acting on the body. For a spacecraft, these forces are of three types: propulsive force (usually provided by the vehicle's engine thrust); gravitational force exerted by the Earth or other celestial bodies; and aerodynamic lift and drag (when flying in the atmosphere of the Earth or other body, such as Mars or Venus). The vehicle's attitude must be taken into account because of its effect on the aerodynamic and propulsive forces. There are other reasons, unrelated to flight dynamics, for controlling the vehicle's attitude in non-powered flight (e.g., thermal control, solar power generation, communications, or astronomical observation).The principles of flight dynamics are normally used to control a spacecraft by means of an inertial navigation system in conjunction with an attitude control system. Together, they create a subsystem of the spacecraft bus often called ADCS.