This article will explain why NASA used kerosene fuel and liquid oxygen to blast the mighty Saturn V. The Saturn V rocket’s first stage carries 203,400 gallons (770,000 liters) of kerosene fuel, 318,000 gallons (1.2 million liters) of liquid oxygen needed for combustion. At liftoff, the stage’s five F-1 rocket engines ignite and produce 7.5 million pounds of thrust.
Is Kerosine like Diesel?
Kerosene is not diesel, but they are both organic liquids. The chain length and branching are different. RP1 is what they actually used, which is a very highly refined version of kerosene, so it is very consistent.
| Rocket Stage | Kerosene (gallons) | Liquid Hydrogen (gallons) | Liquid Oxygen (gallons) |
|---|---|---|---|
| First Stage | 203,400 | 318,000 | |
| Second Stage | 260,000 | 80,000 | |
| Third Stage | 66,700 | 19,359 |
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Which fuel was used in Saturn V’s first stage?
kerolox (RP1 or kerosene and liquid oxygen) was used in the first stage as it is a dense fuel source that gives a lot of thrusts. Thrust is very important in the first stage. You need to have more thrust than your mass to get off the ground. But Kerolox is a dirty fuel, with soot clogging up the turbines, pipes, and valves, which limits the burn time and ignition quantities.
| Measurement | Value | |
|---|---|---|
| First Stage | Thrust | 7.5 million lbs. (3.4 million kg) |
| Burn Time | ~2 minutes | |
| Fuel Consumption | 20 tons (40,000 lbs. or 18,144 kg) per second |
When in space for a few hours, the kerosene essentially freezes, limiting operational time. Also, it is less efficient (lower specific impulse) than some other fuels. So RP1 has more power, but it clogs the rocket motor.
That is liquid methane and oxygen. It provides almost the best of both worlds. Relatively high efficiency and fairly high thrust. Also, it doesn’t produce the soot that kerosene does, as the carbon, once stripped of the hydrogen, is elemental rather than essentially small pieces of coal. This is one of the reasons that all the next-gen rockets are going methalox.
Why did they use liquid hydrogen and oxygen?
Hydrolox (liquid hydrogen and oxygen) has less thrust than kerolox, and hydrogen is a low-density fuel, even when liquefied. However, it has very high efficiency (specific impulse). After you effectively leave the atmosphere, thrust is less important, and that leaves efficiency (specific impulse) even more important. Additionally, liquid hydrogen and oxygen don’t practically freeze in space, at least not like kerosene. This makes hydrogen ideal for major burns during flight in space.
Why use Kerosene for Saturn V?
Kerosene has the advantage that it is storable but at the cost of not providing as much oomph (quantified as a specific impulse) when burned with oxygen, as does hydrogen, which is a liquified gas that boils off. Kerosene is also denser than liquid hydrogen, reducing the volume (and hence weight) of the associated tankage, a significant portion of the rocket’s dry weight. Hydrogen is significantly lighter, however. With kerosene, all the extra carbon atoms bonded to the hydrogen atoms make the liquid well-behaved, but they also weigh things down.
How do you sort out the relative advantages and disadvantages of the two?
When introducing liquid hydrogen fuel to a rocket design, the greatest advantage is realized first by using it in the top stage, where every pound saved up top results in many pounds saved in the lower stages. If the most significant advantage comes from using hydrogen (which was sometimes distinguished early on with the term “high energy propellant”) in the upper stage(s), then the lowest stage tends to be most tolerant (in terms of the overall performance of the rocket) of lower energy fuel like kerosene, which had become the conventional fuel in most large rockets in the 1950s.
That’s why hydrogen fuel first made its appearance in a brand new upper stage (the Centaur) atop an Atlas rocket in the early 1960s. The F-1 engine used in the Saturn V (as well as the entire SI-C stage) was a product of that evolution. But the upper two stages, the S-II and the S-IVB, subsequently developed by North American and by Douglas, respectively) took advantage of hydrogen fuel and the new hydrogen-burning J-2 rocket engine.
You see something similar with rockets over the years that use solid boosters (more recently including some variants of Atlas, Delta IV, the Space Shuttle, and SLS), where high thrust but lower-energy solid propellant boosters are used briefly at the beginning of the flight to help get the vehicle going. Still, comparatively higher energy propellants (kerosene/oxygen core stage with a hydrogen/oxygen Centaur upper stage for Atlas, and just hydrogen/oxygen with the other examples I mentioned) are used later in the flight.
Again, lower stages are more tolerant of lower energy propellants in terms of overall rocket performance. For SpaceX’s Starship, methane is a sort of up-and-coming intermediate choice. There are some carbons bound to the hydrogen atoms, but not as much as with kerosene. The boiling point is higher than with hydrogen, so it’s a bit less volatile in terms of boiloff, and the density is higher. Also, considering that methane might be manufactured in situ on Mars, there are some exciting possibilities.
Specific impulse and power. Kerolox is a power mix (great for the first stages). Hydrolox gives you the best possible bang-for-buck (best mileage, so to speak, the highest efficiency) chemical rockets can give you. I think it is worth including that LH was not used for the first stage because the containment mass required for the extra volume (LH having nowhere near the density of RP-1) would have seriously reduced the available payload far too much.
Kerosene and LOX produce more specific impulse or thrust than LH2/LOX burning, which is what you want to get a 4 million pound rocket off the ground. However, in space where it is cold, kerosene fuel would freeze solid, whereas the liquid hydrogen would still remain a pumpable liquid because of its low melting and boiling point.
What did the V-2 rocket use for fuel?
The original V-2 rocket used ethyl alcohol (in essence, grain alcohol, but also known by the nicknames of “torpedo juice,” “moonshine,” and “white lightning”) and LOX, yet later, the U.S. Army switched to RP-1 (an ultra-refined form of jet fuel — JP-3 and JP-4) which yielded a higher thrust than the ethyl alcohol.
Liquid hydrogen, despite being less dense than LOX, provides a higher specific thrust than RP-1 and is useful for upper rocket stages (S-II and S-IVB stages of the Saturn V; the Space Shuttle after SRB separation, the Centaur upper stages used on the Atlas, Titan III/34-D, and Titan IV, and the similar Delta Cryogenic Upper Stage for the Delta IV and Delta IV-Heavy, along with the planned Earth Departure Stage for the Block 2 SLS).
The only drawback of LH2 (as well as LOX) is the “boiling off” of the propellants; not an issue with RP-1 as it can be stored at room temperature. That is, in part, why the U.S. Air Force replaced the Atlas ICBM with the Titan II ICBM (which uses hypergolic propellants that combust on contact, much like when chlorine mixes with ammonia), the U.S. Army replaced the Redstone IRBM with the solid-fueled Pershing missile. The Navy adopted the solid-fueled Polaris SLBM.
If you want to know more about the mighty Saturn v, head over to this article named: Why Was The Saturn V Rocket Painted Black And White?
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