That figure—the distance separating the Earth and the ship at the top of her orbit—was directly related to how much velocity she had at the bottom. Because Ymir had "fallen" in from an extremely high apogee, far beyond the moon’s former orbit, she had come in screaming hot for her skip off the atmosphere. Every bit of velocity that was killed by the huge nuclear retro-rocket burn, or by friction with the air, translated into a lower altitude at the succeeding apogee, which—depending on how the numbers had worked out—would occur weeks, days, or hours later.