Finally, the boarding call came—delivered in person by a shapely, and decidedly mammalian, flight attendant—and we started to make our way through the priority boarding tube. This was a transpex cylinder—scrubbed so clean you could see the walls only by the way they diffracted lights outside—which extended from the terminal building to the first-class passenger door of the suborbital. Twenty meters away was another, similar tube—which suddenly reminded me of those "HabiTrail" things kids use to incarcerate gerbils—used by the declasse from the economy-class holding pen.