In sharp contrast to satellites in LEO, trajectory design for interplanetary missions is important to the extent that it sometimes provides the main impetus for the mission itself (eg Voyager I & II in 1977, Mars Express in 2003). It is a nontrivial targeting problem the solution of which determines key mission parameters such as launch window time and duration, mass of consumables, mission duration and, through all these, project cost.
In the course of this talk I will discuss the various approximations that one can take in solving for a trajectory between two bodies in the solar system.
I will show that a standard Hohmann transfer, commonly used for small manoeuvers in LEO, is not rigorous enough to be used in inteplanetary trajectory design as the coplanar circular orbit boundary condition breaks down.
I will introduce the Gauss method for producing transfer trajectories between any two keplerian ellipses and discuss briefly the concept of patched conics.
With the aid of results I have obtained in the cases of Earth->Mars and Earth-> Venus trajectories I will discuss the strategies and quantities relevant to the overall feasibility analysis of such missions in the next 10 years.