Understanding Today’s Rocket Propellants
You generally don't want to be blasted to space atop a 200-foot metal cylinder filled with 549,000,000 grams of “some type of” highly explosive propellant. So let's get to know it a bit.
Space Agencies can’t be using jet fuel to propel their rockets … right??
Well, they definitely don’t just go to jet fuel suppliers and use that for their rockets, but what they do use is something very similar. They use RP-1, or Rocket Propellant 1. Both Jet [Fuel] A and RP-1 are highly refined kerosine, but technically RP-1 is understandably more refined, as you would hope.
So, the rocket is just a big chunk of fuel in a tank? No, and yes. There is another type of propellant needed to power the rocket, which is liquid oxygen (LOX). LOX is used as an oxidizer because on earth, all fires need is fuel because the oxygen is in the atmosphere. In space, there is no oxygen, so the rockets need to carry it up themselves, hence, liquid oxygen.
There’s more to rocket propellant than RP-1 though. The other common methods are hydrogen and methane. There are many many more, but they are not as common in the rockets we see today. To the ones I did name, they work very similarly.
The Engine
To understand the fuel, we need to understand the engine. The most common engine is the open cycle rocket engine. An example of this is the SpaceX Merlin engine. Essentially, the way this works, is fuel and oxidizer are pumped and thrown into a combustion chamber. Those pumps are powered by a turbine connected to a shaft that is also powered by a mini combustion chamber, AKA the preburner. The exhaust of the preburner is sent out on the side of the engine. (see the above graphic) Additionally, if you are wondering about the environmental cost of all this check out this article.
How much?
Now, how much fuel is in a rocket? One of the best rockets out there is the standard Falcon 9 SpaceX rocket. It has the capacity for 362,600 kg of Liquid Oxygen and 155,800 kg of kerosine RP-1. Next, Saturn 5, the rocket that carried the Apollo missions to the Moon. This one, larger with more power (understandably) has the capacity for 2,100,000 kg of kerosine in the first stage (versus the 155,800 kg of kerosine from Falcon 9).
Solid!
Solid rocket boosters (SRBs) are extremely powerful but are unique from propellants like RP-1. As you may have guessed, it’s solid fuel, meaning that it’s like a firecracker. There’s also a motor, which propels the fuel down. They are always used in the first stage and help with the atmospheric ascent. In the space shuttles, the SRBs provided about 71% of the thrust. They consist of a lot of different chemicals, but the main components are ammonium perchlorate, the oxidizer, and aluminum, the fuel.
Creation
Ok, so how is it made though? Going back to liquid fuel, the main ones were: RP-1, methane, and hydrogen. I’ve already touched on RP-1 a bit, but to repeat myself, it is highly refined kerosine, very similar to jet fuel. It has a lower specific impulse than hydrogen but is much cheaper, and desnser. Hydrogen is really great. It has the lowest molecular weight of any known substance and burns at extremely high intensity. It also has the highest specific impulse and efficiency out of all known rocket propellants. The issue is that it is cryogenic, meaning that it is a gas that can only be liquified at extremely low temperatures. This obviously poses an issue in space, where the sun produces enormous heat. Methane is used in SpaceX’s BFR aka Starship. It is argued by some to be the fuel of the future because it is much cheaper to produce and efficient at the same time. It is also easier to produce than other fuels, like RP-1 which must be highly refined.
For more info, check out this article for the future of space travel.
Key takeaways:
- Liquid fuels and SRBs need an oxidizer to ignite in space.
- There are many fuels for rockets, but for SpaceX’s Starship that will go to Mars, it uses methane fuel.
- Hydrogen is the most powerful propellant.
