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Science & Technology

Rockets: Fuels and Propulsion

Chris Hadfield

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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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....


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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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Comments

Bernardo F.

This was complicated, I have to admit. I knew that working with rockets is not easy stuff, mostly because of how mass changes due to the changes in the volume of fuel, but I'm not sure I've caught everything haha. Gotta watch it again slowly later.

Mary L.

I love this class! I have been telling my friends about experiencing lift off and going into orbit. Chris Hadfield makes it so easy to understand this very complex subject.

Kevin G.

I'm trying to understand the ion rocket part of the lesson. Am I understanding it right that the basic premise is to kinda "magnetize" the fuel and use something like a magnet to push the fuel out faster? The way I'm kinda envisioning this is if I got a bottle of water, held it upside down, and removed the lid. That would be like a normal rocket. But if I was to cut a hole on the bottom of the water bottle (remembering that it's upside down so it's facing up), insert a straw and blow air into it, it would push the water out faster. Am I envisioning this correctly? I'm a very visual learner. I know that's not the scientifically best example, but that's what came to my mind. Thanks!

William D.

Nothing mentioned about the pros & cons of the various types of rockets propellants. No mention about what specific impulse is and how rockets efficiency is rated. Solid fueled rockets can't be stopped once they're started. Yes, Kerosene and Liquid Oxygen is good but Liquid Hydrogen & Liquid Oxygen is much better. Higher specific impulse. While Hypergolic's are mentioned it isn't explained that they explode on contact. This eliminates the need for an ignition source. However; they're extremely toxic. Also, I believe solid boosters were used on Shuttle strictly due to cost. Nothing is mentioned about Nuclear and the NERVA program from the 1960's. NASA was ready for flight testing and it never happened. That would make a trip to Mars last a few weeks instead of months. ION engines are very efficient but have extremely low thrust levels at this time. By the way, the F-1 engine (Kerosene & Liquid Oxygen) produced 1.5 million pounds of thrust. We can build liquid engines to rival solids.

Mário Filipe P.

This might have been the most challenging lesson so far, just because of the amount of new information I'm getting from it. It's really surprising how deeply the design and the capabilities of your spaceship are affected simply depending on the type of fuel you'll be using. We'll definitely need to come up with new solutions to propel our spaceships as we venture ourselves further into deep space.

A fellow student

Great again. I could feel de power on my back and vibrations during acceleration time.....until sudenly peace become present. Incredible. When Chris was talking about Sir Issac Newton, he say, Gravity is a forcé, I thought, that is a lie. Certainly, now we know Gravity is the deformation of the space/time, is not a forcé. But never a lie was so useful

Kaarthikeyan K.

Chris makes it all so accessible. I was just curious when I started the first video, and now I'm hooked!

Alex K.

Pretty captivating stuff. I would appreciate these lessons even more, with some digital modeling to support the information being put forth. I'm a very visual learner.

A fellow student

Hi, I have a question. In the 11:06 from the video, Chris said that you need to change your speed to 6.6 km/s (delta-V). That's right?. The orbital velocity is 7.9 km/s and the escape velocity is 11.2 km/s. Where does the 6.6 km/s come from?

Maddie W.

Very useful to have these concepts presented in such a clear and engaging way. It makes it easy to understand why these things are important and how they affect rocket design. I really feel like we are learning how to see the world through an engineer's point of view. Chris has an excellent ability to explain these tools and convey that perspective.