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In this answer the following graph is displayed:
It shows two slight increases in altitude (after 1st peak g and at the end of the blackout). For me, it looks like zoom climbs (trading kinetic energy (velocity) for potential energy (altitude)) made to slow down the space craft, but I cannot find any evidence.
What is the purpose of these climbs? Is it to slow down the spacecraft? Is it a common maneuver used during reentry (i.e. is the Apollo spacecraft the only one performing such maneuver)?
Certainly trading kinetic energy for potential energy is an inevitable part of the process. In general this is important in controlling heating and g-forces. A fully ballistic re-entry would have only one (high) max g-force. Attempting to "pull-up" to achieve this is pretty universal. Its worth noting that there is nothing special about an ever-so-slight inflection of the trajectory, its all a spectrum.
That said, its unlikely that bobbing is ever the truly optimal solution, but the causes to do so range from: adding scope for altering trajectory, to being conservative on risking dipping too deep too soon and having too high peak g-force or heating.
As the actual trajectory is a result of all these competing factors, and the (in-)accuracy, of implementing them its unlikely you'll get a short and accurate answer for exactly "why" a particular path was taken.
