Saturn-V for Dummies Part-3: Engines The Dynamic Frequency
Inside the F-1 engine

Hey again everybody, in our journey about studying the mighty Saturn-V, till now we saw the history of its development and got a basic overview of the rocket if you haven’t read them yet, I highly recommend going through them now as the previous blogs play a vital role in setting up the context of this blog. But what is this blog really about? As is evident from the topic mentioned above, we’ll be learning about the engines today. A vehicle can only be called a rocket if it has a rocket engine, rocket engines are reaction engines meaning that spew out fluid that propels the rocket as a result of the reaction of that spewing. Now the engines need to spew out fluid with a certain velocity to produce force/thrust. The force shall be able to lift the rocket off the ground. From all that we know about the Saturn-V till now, just try to imagine the enormity of the engines that it would have required. Now let’s dive in without much further ado.


The Engines: Or how the Rocket flew to the Moon ?

There were 2 types of engines used throughout the rocket stages. Let’s see them one by one in detail;

F-1 engine:

Saturn-V for Dummies Part-3: Engines The Dynamic Frequency
The F-1 engine on display at the INFINITY science center

The F-1 engine was developed by Rocketdyne as one of the 2 engines (F-1 and E-1) to meet a 1955 U.S. Airforce requirement for a large rocket engine. The E-1 engine however was scrapped as it was seen as a technological dead end. The development of the F-1 engine continued further as NASA appreciated its usefulness.

The engine used RP-1 as the fuel and Liquid Oxygen (Lox) as the oxidizer. Both oxidizer and fuel were mixed in a 2.27:1 ratio and were burnt in the combustion chamber.

Many rocket engines use turbo-pumps to suck the fuel and oxidizer from the pressurized tanks and inject them into the combustion chamber, to spin the pump, the F-1 engine followed a gas generator path in which a small amount of fuel and oxidizer is burnt in a pre-burner chamber which spins the turbine, the exhaust is usually dumped on board. Then the fuel and oxidizer mixture is burnt in the combustion chamber and expelled through the bell nozzle. This mechanism is similar to the one we see in SpaceX’s Merlin Engine but the difference is, the merlin dumps the exhaust onboard whereas the F-1 uses the “cooler” pre-burner exhaust as a heat exchanger to stop melting of the nozzle by over-heating. The “hotter” pre-burner exhaust is then dumped with the main exhaust! Name a more ingenious cooling technique used in any other rocket engine, I’ll wait.

Saturn-V for Dummies Part-3: Engines The Dynamic Frequency
Gas-Generator cycle Engine (F-1 & J-2)

The F-1 produced 6770kN of thrust at sea level and 7770kN of thrust in vacuum. It had a thrust-to-weight ratio of 94:1 (the thrust-to-weight ratio is a performance measure of a rocket engine obtained by dividing thrust by the weight of the vehicle), specific impulse (specific impulse is the ability of an engine to produce an acceleration of 9.81N of force for a certain duration of time for 1kg of fuel and is usually measured in seconds, it is like the mileage of the rocket engine) of the engine was 263s at seal level and 304s in vacuum.

This makes the F-1 engine the most powerful gas-generator cycle engine ever made. In the Saturn-V vehicle, 5 F-1 were used in the booster (S-IC) stage and operated for a total of 150s-163s which propelled the vehicle to the first 61km of its ascent.


J-2 engine:


Saturn-V for Dummies Part-3: Engines The Dynamic Frequency
The J-2 engine on display at London Science Museum

The J-2 engine was a vacuum engine meaning that its performance was better at higher altitudes (outside the earth’s atmosphere) than when operated inside the atmosphere. As a result of which the primary objective of the engine was upper atmosphere manoeuvres and Earth Orbit Insertion or Trans Lunar Injection, hence the engine was designed to be restartable.

The engine burned liquid hydrogen (LH2) as fuel and liquid oxygen (LO2) as the oxidizer with a 5.5:1 oxidizer to fuel ratio in the combustion chamber. The engine’s turbopump cycle is the same as that of the F-1 engine i.e., closed gas generator cycle where the cooler pre-burner exhaust was used as a heat exchanger for the nozzle and then was dumped with the main exhaust.

The engine produced a thrust of 1033.1kN of thrust in vacuum and 486.2kN at sea level. In a vacuum, the engine had a specific impulse of 421s and at sea level, it was 200s which makes sense as it was never made to be used as a sea-level engine. The thrust-to-weight ratio of the engine was 73:18.

In the Saturn-V, 5 of J-2 engines were used in the S-II second stage and 1 J-2 was used in the S-IVB 3rd stage. In the 2nd stage, the engine was burnt for about 360s propelled the vehicle to an altitude of 185km, and provided a near orbital velocity of about 25000km/h. In the 3rd stage, the J-2 burnt for about 165s and made the EOI and TLI maneuvers.

Saturn-V for Dummies Part-3: Engines The Dynamic Frequency
The J-2X engine

The J-2 engine was one of the most reliable engines NASA ever had. The next-gen J-2 (J-2X) engine was considered for the Earth Departure Stage of the Space Shuttle program.

As we saw the stats of the engine used in the Saturn-V vehicle are incredible and straight out insane. Well, then you might be wondering what was the purpose of the vehicle? Why did we need such incredible power? We already know it’s the Apollo program, yes, but was the vehicle only used for taking humans to the moon? Well, no. So, this sets up the context for our next article. In the next article, we’ll be learning about the missions and accomplishments of this beast of a launch vehicle. Once it is published, the link will be available here.

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To know the basics of the quantum world, astronomy and space exploration you can check out the book "Through the wormhole" on amazon kindle by Ratnadeep Das Choudhury.

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                                                                             -Ayushman Dash

                                                             Chief Space Exploration Writer
The Dynamic Frequency