The F-1 Engine: Aerospace Engineering Marvel
How was the Apollo program nearly brought shakingly to a halt?
When Kennedy set the challenge to get to the moon by the end of the 1960s, engineers had to figure out how to build a rocket that could produce the 7.5 million pounds of thrust necessary to lift 3 astronauts and two spacecrafts into space without blowing up. It was a tall task without any instruction manual. Enter, the most powerful rocket engine ever developed: the F-1.
The Saturn V rocket was developed by Wernher Von Braun, a former Nazi rocket scientist recruited by the US to build rockets for our military and space program. He was considered the father of rocket science and he led the team of propulsion engineers at NASA’s Marshall Spaceflight Center (MSFC) in Huntsville, Alabama and Rocketdyne, who would develop the F-1 engine. Von Braun had already built a successful rocket for Germany in World War II, the V2, but the Saturn V required a much bigger engine.
The development process was long and difficult with plenty of trial and error. The early F-1 prototypes burned a volatile mixture of liquid oxygen and kerosene and suffered from combustion instability, or uneven burning of the rocket fuel. The first several times they tested the engine it blew up. Sonny Morea, project manager for the F-1 engine at NASA, recalls what was at stake: "If we couldn't solve the combustion instability problem, we would have stopped the program. It could not have gone forward, we would not have gone to the moon, It was too risky. We would have killed a bunch of astronauts trying to make that work."
The first Saturn V launches, Apollo 4 and 6, were unmanned and a bit shaky (literally). The rocket experienced severe shaking known as pogo oscillation, like a pogo stick, caused by the combustion instability problem. Engineers threw everything but the kitchen sink at the problem and finally adopted a fix inspired by Von Braun’s V2 engine called baffles, which separated the fuel flow and calmed down the engine. This was critical as during the 2.5 minutes the Saturn V's five F-1 engines would burn 15 tons of fuel per second to get the rocket to the 6,000 mph speed necessary to reach the right orbit for a moon voyage.
The heart of the engine was the thrust chamber, which mixed and burned the fuel and oxidizer to produce thrust. A domed chamber at the top of the engine supplied liquid oxygen to the injectors, which directed fuel and oxidizer into the thrust chamber for mixing and combustion. An incredibly volatile chamber that had to be tested to perfection. While the Apollo 6 launch was a bit shaky, when they launched the rocket again with its first human crew on Apollo 8, they had fixed the pogo problem.The crew of three made it safely to the moon and back. By the time Apollo 11 launched to the moon in July of 1969, the Saturn V was flying smoothly. During the remaining Apollo missions and subsequent launches the Saturn V and F-1 engines never experienced a failure. It was perfect, and the F-1 engine still holds the record as the largest single-chamber, single-nozzle liquid fuel engine ever flown.
Eric Tepool, a second generation propulsion engineer at NASA MSFC today is amazed at what engineers were able to do with limited technology 50 years ago: "I definitely marvel at what they did back in the day -- they didn't have personal computers sitting on their desks, they used slide rules – they didn't have they modeling capability that we have today so I'm really amazed at what they were able to accomplish with the tools they had in their tool box versus what engineers have today."
As NASA looks to manned missions to the moon and mars, they are developing a new rocket called Space Launch System (SLS). It will require a modern version of the F-1 and NASA engineers have even pulled an old F-1 engine out of storage to learn how to build the next big thing even better by studying this incredible engine with a perfect flying record.