The point in a lunar orbit nearest the surface of the moon is called perilune and the point farthest from the surface is called apolune.

The Apollo 11 spacecraft was placed in an elliptical lunar orbit with perilune altitude .

Apolune altitude .

The radius of the moon is .

The center of the moon is at one focus.

The ellipse equation is .

The point on the ellipse closest to a focus is the closer vertex while the farthest point is the other vertex .

So for this lunar orbit,

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.

Consider .

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Substitute and in .

.

The ellipse equation is .

The ellipse equation is .