As they had done with Ymir, they mined ice from the interior volume of Endurance, leaving the outer "walnut shell" as a structural support and as a first line of defense against bolides. But as J.B.F. and other Dump and Run partisans had never tired of pointing out, such a heavy craft lacked maneuverability. When a big rock was seen far enough in advance, they could use her engines to make small course changes that would have large outcomes by the time the rock came close. Doing so was the full-time occupation of most of Endurance ’s complement, which worked at it three shifts a day. But below a certain threshold they could not see rocks soon enough, or maneuver out of their way quickly enough, and then they just had to hope that the bolide would strike Amalthea. Most did, but some hit the icy lower slopes, and of those, some struck with enough power to penetrate and kill.