5 - The drivers for the approach strategy

Summary

The major natural and technical features and constraints which (along with trajectory safety) are the driving forces behind the design of the approach strategy will be discussed in this chapter. The consequences on trajectory elements and approach strategy for the various natural and technical issues will be indicated. Trajectory safety remains the over-riding requirement; this always has to be kept in mind when discussing all other potential design drivers. Three examples of approach strategies with different constraints are discussed at the end of the chapter, for which, within the context of a complete approach scenario, a detailed explanation of the rationale behind the choice of trajectory elements of the different rendezvous phases is provided.

Overview of constraints on the approach strategy

The most important disturbance which has to be taken into account in the launch strategy is the drift of nodes due to the J₂-effect, described in section 4.2.2. Because of the difference in orbital altitude, this drift will be different for chaser and target over the duration of the approach. The difference will therefore have to be compensated for by corrective measures during launch and phasing. The phasing strategy is mainly driven by the difference in position between the target station and the chaser vehicle after launch and by the required arrival time at the target.