YMIR ’S COMMAND MODULE WAS ARKLET-SIZED. OF COURSE, THAT went for almost everything now in space, since an arklet was just the biggest object that could be launched into orbit on the top of a heavy-lift booster. Some arklets were "tunnel," meaning that they were laid out in a "horizontal" orientation, meant to lie flat, as it were, like railroad tank cars, with a single long floor running from end to end. This was good if you wanted a large open space, but tended to be a less efficient use of available volume. The command module of Ymir, like that of New Caird, was "silo," meaning that it was oriented in a "vertical" way, diced into a number of round stories—typically four or five—joined by a ladder. Each story was a fat disk of space about four meters in diameter, big enough for one room that would be considered large by space travel standards, but more often divided into smaller compartments.