Stone said, “Thirty-five thousand feet. Going through Mach one point nine. SRB combustion chamber pressure down to fifty pounds per square inch.”

“Copy,” John Young said from the ground. “You are go for SRB separation.”

“Rog.”

She heard a faint, muffled bang; the cabin shuddered, rattling her against her restraints. Separation squibs had fired, pushing the exhausted solid boosters away from the main stack. She felt a dip in the thrust; but then the acceleration of the MS-IC’s central liquid boosters picked up again, and she was pressed back into her seat.

“Roger on the sep,” Young said.

“Smooth as glass, John.”

The solid boosters would be falling away like matchsticks, dribbling smoke and flames. The strap-on solid boosters were the most visible enhancement of the VB over the core Saturn V design; with their help the VB was capable of carrying twice the payload of the V to Earth orbit.

“Five thousand one hundred feet per second,” Stone said. “Thirty-three miles downrange.”

She glanced at the G-meter. Three times the force of gravity. It wasn’t comfortable, but she had endured a lot worse in the centrifuge.

Cool air played inside her helmet, bringing with it the smell of metal and plastic.

With the SRBs gone, the ride was a lot easier. Liquid motors were fundamentally smoother burners than solids. She could hear the mounting, steady roar of the MS-IC’s engines, the continuing purr of the Command Module’s equipment.

Everything was smooth, ticking, regular. Inside the cosy little cabin, it was like being inside a huge sewing machine. Whir, purr. Save for the press of the acceleration it was unreal: as if this was, after all, just another sim.

“Three minutes,” Stone said. “Altitude forty-three miles, downrange seventy miles.”

“Coming up on staging,” Gershon said. “Stand by for the train wreck.”