A gray curtain started closing in on her vision, as if sweeping in around her head. It was the first symptom of blacking out. There was an array of colored lights on a panel in front of her so she could tell how far gone she was. When she relaxed, the gray curtain was prominent; when she tensed herself up the curtain would disappear. She tried to ignore the pain in her chest; but every time she raised her arms or moved her head she felt giddy. That was the Coriolis force — the sideways force associated with fast rotation.

York was in the middle of a series of simulated reentries from Earth orbit. This particular exercise, the worst of the set, was modeling a high, steep trajectory, as if her Command Module were cutting into the layers of Earth’s atmosphere too rapidly, and so undergoing terrific deceleration.

When she reached eight Gs, she found she couldn’t raise her arms anymore. She could only lie in the cage and endure it.

Then the gray curtain around her eyes was thickening, and it wouldn’t go away.

Of course it’s worse than a real mission. The damn doctors design it that way.

Her vision started to blur. She found it hard to read her instruments. Twelve Gs; far higher than anticipated during a real mission. Enough to flatten her eyeballs. Her head was being battered against the inside of her pressure-suit helmet. The lights of the lab beyond the cage whirled past the mock-up cabin’s small windows.

Fifteen Gs. She couldn’t breathe at all. She became sure she was going to black out. But I’m only halfway through the run. And the doctors were watching her, every twitch of her flattened face, on closed-circuit television.

At last the load began to drop away; the pressure eased from her chest, and she sucked in great gulps of air.

Of course, nobody would complain about being subjected to high-tech torture in instruments like the Wheel, or query the relevance of all these exercises to actual spaceflight, or — still worse — admit that he or she had any problems with the routines. Because if you complain, it’s bound to get back to Muldoon, and a note will go into whatever damn system he uses to select his crews, and you’ll never get off the ground.

And that was the name of the game at the moment. Joe Muldoon, in his new role as head of the Mars program, had also assumed unto himself the old, separate function of director of Flight Crew Operations.

It was Muldoon who assigned crews to missions. And everyone knew that Muldoon was in the middle of drawing up his crew rota for the first flights in the new program, leading up to the Mars mission itself; the only thing that mattered in life right now — the only thing — was getting a berth in that rota.