Sorry I deleted my comment because I had already discovered the answer.
(I asked what the meaning was when an orbit is written as XXXxYYYkm.)
From my reading of both articles together, I'm pretty you're correct - it's the interval that the satellite's altitude moves between (ie the axis's on the ellipse around the Earth, like you say)
(I asked what the meaning was when an orbit is written as XXXxYYYkm.)
From my reading of both articles together, I'm pretty you're correct - it's the interval that the satellite's altitude moves between (ie the axis's on the ellipse around the Earth, like you say)