At this moment the noise and tremors reach the first of the million or so spectators who have made the pilgrimage to Cape Canaveral. The shock wave from the Saturn V literally shakes them to the core. The pressure blows the glass panes out of a building 10 miles away. Even in New York City—1,500 km as the crow flies from the launch site in Florida—where about 10,000 people have gathered in front of a massive television screens in Central Park, seismometers registered the tremors. During the rocket’s first test flight two years earlier, the launch knocked ceiling panels to the floor in the press center located 5 km from the launch pad.
It could have been even more extreme. The engineers could have gotten more thrust for the rocket by combining liquid hydrogen cooled to -253°C with liquid oxygen. But this technology was considered too risky and not mature enough in the early 1960s, when the main engines were designed. In any case, a brand-new assembly had to be developed. One that is still today—more than 50 years later—considered the most powerful single engine ever built. Instead of relying on volatile hydrogen, the Saturn V engineers turned to a proven solution with a little less thrust: They combined ultrapure kerosene with liquid oxygen—a blend that the Soviets used to safely launch Yuri Gagarin, the first human to go into outer space.
13 tons fuel consumption per second
Kerosene held another advantage for the American engineers. Because it is denser than hydrogen, a smaller tank could be used that was also easier to design. The tank was gigantic nevertheless: To make room for almost 600 tons of kerosene, the tank had to be 13 meters high—taller than a single-family house.
And the oxygen tank right on top of it was even bigger. At 20 meters long, it held 1,250 cubic meters of the liquid gas—enough to fill a 50-meter swimming pool. Because pure oxygen is extremely reactive—even a single fingerprint left on the walls of the tank can cause an explosion—it had to be perfectly clean: The tanks were first rinsed, then treated with acid, rinsed again, milled, air dried, and finally chemically treated again.
The tanks could only be so big, and with 13 tons of fuel per second forced into the five engines, their contents last for only a short time, even as they created an exhaust plume almost 300 meters long soon after launch. The Saturn V reaches an elevation of 70 km and can still be seen easily with a pair of binoculars after only 2 minutes and 41 seconds, but time is already up for the first stage.
This early finish is entirely intentional. A single rocket would be too heavy to ever reach the speed needed to transport a 50-ton spaceship to the moon, so the Saturn V consists of three stages—basically, three stacked rockets, each smaller than the previous one. After the first stage—with its enormous tanks and five engines—burns out, it is separated and falls back to Earth. The remaining rockets, now with only one-third the original launch weight, continue the journey.
Saturn V – one of the safest rockets to this day
The three men in the cramped capsule later report in their log that the stage separation feels like a train crash. The astronauts are hurled forward as the engines of the first stage, which had been pressing the crew down into their seats with four times their body weight, fall silent. Only their seatbelts prevent the astronauts from crashing into the capsule’s instrument panel. The second stage ignites, and they’re pushed back as the rocket accelerates again.
Since lighter rockets require less thrust, the engines for the second stage do not have to be as high powered or complex as the first stage. So, the rocket scientists led by German engineer Wernher von Braun took a risk and used hydrogen instead of kerosene.
They obviously weighed the dangers carefully: The Saturn V is considered to this day to be one of the safest spaceships ever, with 13 launches, include 10 with people, without a catastrophic error. But the flight of the biggest, heaviest, and most powerful of all the rockets yet launched was not without its problems: The mixture of fuels, which was forced at 60 bar through the more than 3,000 holes in the engines’ combustion chambers, often burned in an unstable manner. Some engines exploded on the test stand. The solution was simple: Technicians bored additional holes in the head of the combustion chambers in a random pattern, effectively reducing the oscillations, and the problem disappeared.
A new problem emerged during the first test flight, one that especially affected Apollo 13: The fuel began to vibrate and the whole rocket hopped like a pogo stick. For safety, the middle of the five engines shut itself off. Luckily, the on-board computer, which was capable of only 12,190 operations per second, more than a million times slower than a modern processor, let the other engines run longer. The mission would come up against more problems later in outer space, but the Saturn V launch was saved.