Chapter 6 - Orbital Maneuvers

Abstract

Orbital maneuvers transfer spacecraft from one orbit to another. Orbital changes can be dramatic as the transfer from a low-earth parking orbit to an interplanetary trajectory can also be quite small, as in the final stages of the rendezvous of one spacecraft with another. Changing orbits requires the firing of onboard rocket engines. This chapter focuses on impulsive maneuvers in which the rockets fire in relatively short bursts to produce the required velocity change. Impulsive maneuvers are those in which brief firings of on-board rocket motors change the magnitude and direction of the velocity vector instantaneously. During an impulsive maneuver, the position of the spacecraft is considered to be fixed and only the velocity changes. The chapter presents the classical, energy-efficient Hohmann transfer maneuver, and generalizes it to the bi-elliptic Hohmann transfer to see if even more efficiency can be obtained. The Hohmann transfer is the most energy efficient two-impulse maneuver for transferring between two coplanar circular orbits sharing a common focus. The Hohmann transfer is an elliptical orbit tangent to both circles on its apse line and helpful in sorting out orbit transfer strategies to use the fact that the energy of an orbit depends only on its semimajor axis.