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Distances are expressed centre to centre.
Earth-Moon laser travel time measurement will be surface to surface but the distance will still be expressed centre to centre i.e. radii added back in.
Consider the Sun. The planets orbit the Sun in an elliptical path with the Sun at one focus. The furthest a planet is from the Sun is a+f, where a is the semi-major axis and f is the Sun's offset from the ellipse's centre. The closest a planet is from the Sun is a-f. The average of the two is (a+f+a-f)/2=a, which is the semi-major axis.
Regards, Rob.
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