The Earth-Mars distance ranges from 56 million to over 400 million kilometers, depending on where the two planets sit on their orbits. One might assume that this distance is what determines the cost of a trip. That is false, or nearly so: what costs energy is not crossing interplanetary space, but tearing free from the bottom of a gravity well, or plunging back into one. This distinction, gravity rather than distance, runs through the entire Deimos-II / Eagle-One architecture