Now thrust could be generated (for “free” again) at periapsis, progressively increasing the altitude of apoapsis.

这时可以「免费」在近心推力，渐渐将心的高度。

The repeated thrust applications at apoapsis would raise periapsis from inside to outside the stationary orbit.

复在心施以推力，会将近心由同步轨道内到同步轨道外。