And, of course, that sense of awe was piqued on this occasion by his foreknowledge of the fate of Booster AS-5B04, just a few seconds later.
Udet glanced around. Joe Muldoon, up on the stage with Dana, was moderating the meeting, and much of NASA’s senior management appeared to be in attendance; there were staff from Marshall and Houston and NASA Headquarters, including aides of Tim Josephson, and a heavy representation from the contractors responsible for the system components under scrutiny today.
The presentation was to be a summary of NASA’s preliminary internal report into the problems encountered during the launch of Saturn VB stack AS-5B04, three months earlier. Depending on the reaction of this audience, and on the NASA hierarchy as a whole to the content of the report, a draft would be finalized and published within the week.
There was an air of tension, anxiety, weariness.
Coming so soon after the Apollo-N tragedy, nobody in the Agency wanted to face up to another disaster, the first loss of a Saturn. Udet had heard the muttering. Who the hell can we blame for this one?
Dana was speaking, in his thin, frail voice. Udet drew a little more upright in his chair.
“At 6.6 seconds before launch, the Saturn’s kerosene-fueled F-1A main engines were ignited in sequence and run up to full thrust, while the entire structure was still bolted to the launchpad. The thrust of the main engines pushed the Saturn assembly upward, against the restraint exerted by the pin-down bolts anchoring it to the pad. When the Solid Rocket Boosters’ restraining bolts were explosively released the stack’s ‘stretch’ was suddenly relieved…”
On the screen behind Dana, clouds of smoke and steam billowed up around the base of the Saturn stack. Then the four Solid Rocket Boosters ignited, and yellow-white fire plumed from their engine bells. The camera shuddered, as testimony to the acoustic energy spewed out by the stack — but the film was without sound, and the brilliant launch sequence worked through in eerie silence.
The image froze. Billows of smoke stopped their evolutions, and became mounds of gray and white, solid-looking, like dirty ice cream.
Around Udet, rows of lined faces were illuminated by frozen rocket light.
An arrow pointed to a blurred patch of white near the base of the MS-IC; it was just below the “A” of the red-stenciled “USA” on the wide hull of the booster.
Dana said, “At 0.687 seconds into the flight, photographic data shows a strong puff of vapor spurting from the lower casing of the MS-IC, just above the engine fairing.” Dana glanced over his shoulder, wrinkling his nose. “As you can see here. The two pad cameras that would have recorded the precise location of the puff were inoperative. Computer graphic analysis of film from other cameras indicated the initial vapor came from that level of the MS-IC where the feed from the oxidizer tank exits the propellant tank.”
The MS-IC contained two huge cryogenic tanks. The oxygen tank was uppermost, and the fuel lower. Fat suction lines carried liquid oxygen through the kerosene tank for combustion in the five huge F-1A engines at the base of the stack. Dana was implying that there had been some kind of problem with that feed.
The film started again, in extreme slow motion; the smoke evolved around the Saturn with glacial slowness. White arrows continued to prod at the offending vapor patches at the base of the MS-IC.
“Six more distinctive puffs of vapor were recorded between 0.836 and 2.501 seconds. The multiple puffs in this sequence occurred at about four times per second, approximating the frequency of the structural load dynamics and resultant stack flexing…”
The wretched “stretch”!
“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…”
Udet massaged the bridge of his nose, trying to control the irritation that flared within him. We know this. My team at Marshall, and the contractors independently, determined this root cause of the fault within an hour of the malfunction. The Saturn had already been vibrating, from the “stretch,” at three or four cycles a second just after launch. Then one of the Solid Rocket Boosters had started vibrating lengthwise, at about the same frequency. Such oscillations had been observed before. But the coincidence of frequency was unfortunate, for that frequency, as it turned out, had been just right to set up standing waves in the valve system carrying liquid oxygen into the main engines…
We know all this, and we are already working to correct the problem. Have you no more wisdom to add than this, Dr. Dana?
But Dana was continuing; he was describing how some preliminary tests, carried out during the MS-IC’s design stage, had indicated the possibility of a resonant flutter — although no change in the stage’s design had resulted — and he even referred to the problems encountered with the Apollo-N flight, when similar resonance problems had caused that stack to pogo.