Science & Tech
Rockets: Fuels and Propulsion
Lesson time 20:59 min
Chris explains the pros and cons of different types of rocket fuels including liquid fuel, solid fuel, and ionized gas.
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Topics include: "Getting a Shirt to Mars • Stored Energy, Fuel, and an Oxidizer • Solids vs. Liquids • Ion Rockets • The Rocket Equation • Additional Fuel Variables"
Like all spaceships, rockets are a compromise design. You're trying to take something to space, and you have a finite amount of fuel inside your fuel tanks, you only have so much ability to steer through the atmosphere, and so you really want this thing we're taking up to be as light and as small as possible, because then you don't need so much fuel. The problem gets harder and harder if you're going somewhere, if, say, you're going all the way to Mars, because when you get to Mars, somehow you have to be able to slow down and land. So you're not just bringing the stuff that you need, but you have to bring another rocket ship up here in the end that will be able to take you down to land on the surface of Mars. And you need fuel for that rocket. And every ounce that is carried on the top is going to take pounds and pounds of fuel to get it away from the world and to slow down when you get to Mars. And it gets even worse, because you got to come back from Mars probably. And where does that fuel come from? Unless you can manufacture fuel on the surface of Mars using the raw materials that are there, that means not only are you bringing enough fuel to leave Earth, but you're bringing enough fuel to leave Earth and slow down and stop at Mars, land on Mars, blast off of Mars, accelerate, come all the way back to Earth again, and then land back on Earth. And it just magnifies on the amount of fuel that you need. So what does it really take, say, to put one thing on the surface of Mars? For every pound that we put on the surface of Mars, it takes about 200 pounds of rocket here on the surface of the world. Most of that is fuel. But for every pound that gets to the surface of Mars, it took 200 pounds to get it off the surface of the world, accelerate it out to the speed, and safely there. So every little fraction of a pound, every ounce that you can save on what it is you're putting on Mars will decrease the size of the rocket that you need to leave the Earth. So let's think. I want my T-shirt to be on Mars. Your T-shirt weighs some fraction of a pound. If your T-shirt weighs, I don't know, a third of a pound, then you need a third of 200. You're going to need, like, 70 pounds of rocket just to get your T-shirt onto Mars. So you really want to be efficient in packing, and thinking about what's the minimum amount of stuff that we can bring to Mars so that we can keep the size and the scale and the complexity and, therefore, the cost of the rocket to be as small as possible. What type of fuel do rockets use? It's varied over time. But essentially, it's fairly similar. We have some sort of fuel in a tank or a solid fuel inside a rocket like this, and then we have the oxidizer or oxygen that's stored in a separate tank. On the Saturn V, the rocket that took us to the moon, these first stages couldn't have been simpler. It was just kerosene. That was the fuel. Kerosene and oxygen. It was a pretty good first fuel, just using kerosene, oxygen....
About the Instructor
Impossible things happen. At age nine, Chris Hadfield knew he wanted to go to space. He eventually went there three times, becoming a commander of the International Space Station. In his MasterClass, Chris teaches you what it takes to explore space and what the future holds for humans in the final frontier. Learn about the science of space travel, life as an astronaut, and how flying in space will forever change the way you think about living on Earth.
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