The first of those burns happened about thirty minutes after she was christened, and yielded a delta vee of four meters per second. The acceleration was so mild that most of the crew could not even sense it. For the combined thrust of eighty-one arklet engines was nearly powerless against the bulk of Endurance, with her roughly equal masses of iron and ice. Nonetheless it was enough to boost her apogee, which occurred some forty-six minutes later, by 14.18 kilometers. And forty-six minutes after that, another burn during another scrape with the atmosphere gained them another four meters per second that, at the ensuing apogee, added 14.21 kilometers on top of that. The result of Endurance ’s first day of operations was a boost in apogee altitude of more than one hundred kilometers, enough to get them clear of the expanded atmosphere except during the few minutes each orbit when they swung through perigee.