On a closed loop from Marshall, a warning was whispered to Mike Conlig. “The S-IC is pogoing. The accelerometers are showing plus or minus eight Gs.”

Conlig was sitting at the left-hand end of the Trench — the front row of the MOCR at Houston — working as the Booster controller for this launch, with special responsibility for the new NERVA stage. The pogo had to be occurring because the natural vibration of the thrust chambers of the F-1 engines was close, somehow, to the structural vibration of the stack as a whole. Christ, he thought. But we put in absorbers to de-tune the vehicle, this shouldn’t be happening. Evidently those assholes at Marshall hadn’t done enough resonance testing on the new Saturn VN stack, with its nuclear third stage. We could lose the mission because of this.

He prepared to report to Flight.

But the whisper from Huntsville came through again. “Amplitude diminishing.”

Conlig held his breath and waited.

The pogoing faded, as suddenly as it had begun.

By comparison, the steady pressure of three or four Gs on Dana’s chest was a welcome relief.

He saw the mission clock, hovering before him. Ten seconds. That’s all it was. Ten seconds.

He turned his head to see the others; there was a zone of blackness around his vision. He focused on Chuck Jones’s face. “Chuck? Ben? Are you okay?”

Jones’s hand was closed tight around the abort handle; Dana wondered what effort of will it had taken to keep from turning it. Jones said, “Houston, we’ve been a-pogoing. But we is still here, like three dried peas in a tin can.”

“Roger.” Natalie York sounded puzzled. It was possible the Houston people didn’t know, yet, what the crew had gone through. They didn’t see the accelerometer readouts. Dana just hoped they were watching the rest of the telemetry.

But then the events of the launch sequence came rushing on them. “Three minutes,” Jones called. “Get set for staging, boys.”

Dana shook his head, and the darkness at the edge of his vision began to disperse. He thought uneasily of the additional stress the staging would place on the pogo-rattled S-NB.

Rolf Donnelly had not enjoyed the pogoing. He had also not enjoyed not knowing about it until the crew’s verbal report came through.

At this stage of the flight, the Marshall people were more or less in control; they had the best understanding of the status of their bird. But I don’t know why we didn’t abort during that damn pogo. They must be really keen to get their nuclear stage into orbit.