They were in a highly eccentric orbit now, a pair of hairpin turns welded together by straightaways a third of a million kilometers long. Earth nestled deep in the crook of one of those hairpins. Endurance ’s perigee hadn’t changed in three years; on every one of the thousands of orbits they had made, they had screamed across the top of Earth’s atmosphere while running their engines full blast. On the last such pass, which they’d made about five days ago, they’d topped out at more than eleven thousand meters per second of velocity. The visual symmetry of the orbit was deceptive; at their current location, the opposite hairpin, now slightly beyond the old moon’s orbit, they were crawling along at a speed that could have been matched, back in the day, by a wheeled vehicle on a salt flat. They were like a car on a roller coaster that had been towed all the way to the top and that was creeping along in that moment before it begins the plunge down to the bottom. The Earth was the size of a ping-pong ball at arm’s length. Soon they’d begin falling toward it, building back up toward eleven thousand meters per second during their next perigee pass, five days from now.