Sealed inside a dummy spacecraft he was slammed into deep pools so that he could practise unhooking his harnesses, opening the hatch, swimming to the surface and activating his survival systems. He was sent up in the Vomit Comet, a converted transport plane which followed elaborate parabolic loops through the sky so that, falling freely inside the aircraft, he could experience weightlessness for twenty or thirty seconds at a time. During the first he was made to sit still, to find out how it was going to feel: like, it turned out, going over the lip of the world’s biggest roller-coaster, and never coming down. On the second loop he was allowed to move around, floating from ceiling to floor, wall to wall. At the end of every loop he had to make sure his feet were on the floor before the plane went into its recovery. He practised moving large masses, throwing a medicine ball to Geena, feeling the reaction as he was pushed backwards. Henry learned how to brace himself, to get the reaction he needed, and to judge the centre of mass of a complex object, to learn to shove and control without sending it rolling.

Then he was put through another flight where he had to do the whole thing again, but wearing a spacesuit.

The next day Geena flew him to Johnsville, Pennsylvania, to the Navy’s Acceleration Laboratory, for a ride in what the technicians here called, cheerfully, the County Fair Killer. It turned out to be a centrifuge, a cage with a seat and other equipment which got spun around inside a circular room. During the launch he would be given a protective G-suit to wear, but for now he had nothing to protect him, save exercises on tensing his muscles and holding his breath, to make his blood pressure well up.

When you thought about it, he realized, a centrifuge was a symbol of the high frontier. Only pilots of high-performance aircraft and astronauts would be accelerated to the rates that kind of centrifuge could provide. He found out later that NASA didn’t even have any centrifuges of its own any more. The Shuttle ride to orbit was so gentle the astronauts were subjected to no more G than you’d suffer on a moderate switchback ride.

On the other hand, during the most crucial stages of launch and reentry, Henry would not be in the hands of NASA.

It didn’t seem so bad when it started. A mix of fairground ride and James Bond torture chamber. But the force was eyeballs-back, as the pilots called it, an intense pressure on his chest, as if a ton of bricks was being piled on there. Breathing got more difficult, and he could feel his face distending. He felt oddly self-conscious; there was a closed-circuit TV camera fixed on his pancaked face through the whole experience.