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<p>minimum-delta-v trajectory corresponds to an ellipse with one focus at the centre of the Earth and the other at the point halfway between the launch point and the destination point (somewhere inside the Earth). (This is the orbit that minimizes the semi-major axis, which is equal to the sum of the distances from a point on the orbit to the two foci. Minimizing the semi-major axis minimizes the <a href="page.php?w=specific_orbital_energy">specific orbital energy</a> and thus the delta-v, which is the speed of launch.) Geometrical arguments lead</p><p>
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