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

这时可以「免费」在近产生推力，渐渐将远的高度提升。

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

复在远施以推力，会将近轨道内提升到轨道外。