This chapter deals with the definitions and basic relations for the propulsive force, exhaust velocity, and efficiencies related to creating and converting energy; comparisons of various propulsion systems and the simultaneous performance of multiple propulsion systems are also presented. The basic principles of rocket propulsion are essentially those of mechanics, thermodynamics, and chemistry. Propulsion is achieved by applying a force to a vehicle, that is, accelerating it or, alternatively, maintaining a given velocity against a resisting force. The propulsive force derives from momentum changes that originate from ejecting propellant at high velocities, and the equations in this chapter apply to all such systems. Symbols used in all equations are defined at the end of the chapter. Wherever possible, the American Standard letter symbols for rocket propulsion (as given in Ref. 2–1) are used.
The total impulse It is found from the thrust force F (which may vary with time) integrated over the time of its application t:
For constant thrust with negligibly short start and stop transients, this reduces to
Total impulse It is essentially proportional to the total energy released by or into all the propellant utilized ...