The gravity turn

One simple control strategy is to align the thrust vector with the velocity vector. If the initial state is at some altitude with a purely horizontal velocity (as from a circular orbit, for example), gravity will add a vertical downwards component. Continuous braking (or atmospheric drag for that matter) means the vehicle eventually loses its memory of the initial horizontal velocity, and the velocity progressively becomes dominated by the gravitational AV added. The trajectory therefore turns over and becomes vertical (it is readily visualised by throwing a table tennis ball). This type of guidance requires knowledge of the vehicle attitude and its velocity.

0 0

Post a comment