“You can also see shock diamonds in the F-1A exhaust, another symptom of the stack resonance. At 3.375 seconds the last vapor was visible below the Solid Rocket Boosters and became indiscernible as it mixed with rocket plumes and the surrounding atmosphere. Other vapors in this area were determined to be melting ice from the bottom of the MS-IC or steam from the rocket exhaust in the pad’s sound-suppression water trays…”

The film began to run at normal speed.

The Saturn tipped away from the launch tower, and rolled, as programmed, onto its back. Udet could see, between the four brilliant stars of the Solid Rocket Booster bells, the pale, almost invisible, smokeless fire of the kerosene-oxygen main engines.

Dana went on, “At this point the first indications were received, via telemetry, of a significant reduction in propellant flow to the MS-IC main engines.”

The image froze again. The audience stirred; the sudden cessation of the launch sequence’s hypnotic flow was jarring. An arrow pointed to the five main engine bells.

“The first visible indication of main engine thrust reduction was detected on image-enhanced film at 58.788 seconds into the flight. It is visible in this frame, as a dimming of the plume from the right-hand F-1A bell — just here.

“One film frame later from the same camera, the reduction is visible without image enhancement.” The engine bell had grown dark, and its four brothers were also clearly ailing. “At about the same time telemetry showed a differential between the pressures in the main engine chambers. The right-most booster chamber pressure was lowest, confirming the growing reduction in the flow of propellant.

“At 62 seconds into the flight, the control system was responding to counter the forces caused by the differential thrusts from the main engines…”

The film ran on, slowly; the main engines flickered or died, but the Solid Rocket Boosters still blazed with fire. The stresses on the stack were enormous as the SRBs tried to compensate for the loss of the main engines.

No change in the attitude of the complete stack was visible to the naked eye. Udet knew, however, that at this point his doomed Saturn was already fighting for its life.

Dana cleared his throat, and pushed his glasses against his face; his gestures were small, precise, almost apologetic. “Analysis has shown that the primary cause of the malfunction evident at this point in the flight was the feeder valves set in the underside of the MS-IC’s oxygen tank, which carry oxidizer into the feeders to the main engines. Tests have indicated that under certain circumstances, the valve design could go into a ‘flutter’ regime and effectively shut off the supply of oxidizer, resulting in a total failure of all F-1A engines. As was observed here. The frequency of the possible flutter has been shown to be close to the frequency of the launch ‘stretch’ and to oscillations caused by instabilities in the burning of the Solid Rocket Boosters…”