Chapter 7 of 29 from Chris Hadfield

Rockets: Fuels and Propulsion


Chris explains the pros and cons of different types of rocket fuels including liquid fuel, solid fuel, and ionized gas.

Topics include: "Getting a Shirt to Mars • Stored Energy, Fuel, and an Oxidizer • Solids vs. Liquids • Ion Rockets • The Rocket Equation • Additional Fuel Variables"

Chris explains the pros and cons of different types of rocket fuels including liquid fuel, solid fuel, and ionized gas.

Topics include: "Getting a Shirt to Mars • Stored Energy, Fuel, and an Oxidizer • Solids vs. Liquids • Ion Rockets • The Rocket Equation • Additional Fuel Variables"

Chris Hadfield

Chris Hadfield Teaches Space Exploration

In 28+ lessons, the former commander of the International Space Station teaches you the science of space exploration and what the future holds.

Learn More


Explore the unknown

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.

Learn about the past, present, and future of space exploration with astronaut Chris Hadfield.

Download the workbook for lesson recaps, assignments, and photocopies of handwritten notes that Chris took to space.

Upload videos to get feedback from the class. Chris will also answer select student questions.


Students give MasterClass an average rating of 4.7 out of 5 stars.

Really quite amazing! I took the class just to learn something new and different. Chris Hadfield is a brilliant teacher and commentator. He is able to explain extremely complex ideas, scenarios, and theories in a simplistic fashion for anyone to follow and understand. I thoroughly enjoyed the course!

Amazing and inspiring. The most interesting course I've ever taken. Thanks to Chris for sharing his wisdom with us.

I find Chris really inspiring. I'm not only super excited about space exploration now that I've heard him talk about it, I'm also thrilled by him as a person. The way he takes his life and his line of work as an example for everything else really gave me a lot of positive incentive to think about what I'm doing. One of my absolute favorites

Chris Hadfield is very well spoken and is very knowledgable. He is also excellent at explaining complex subjects at a beginners level.


Larry R.

This is as close as I've had someone come to making math (especially this level of math) fun for me. Thank you!

Bill M.

The math is so far over my head, but still fascinating. Still, I wish there were more videos and graphics explaining the lessons.

Jim S.

Nice summary of this topic. The fuel is really the limiting factor in many ways. I wonder if astronauts pack lightly in their earthly trips?

A fellow student

First, use a white board with black marker for seeing clarity on a home PC. Second, use graphics with real numbers for clarity of explanation of equations. Third, stop drawing on notebook for explanation use graphics. Fourth, use archive footage to illustrate points during lecture. Being an astronaut does not make you a good teacher to non astronauts.

Jerry R.

Since we have unmanned traffic to Mars, the question is not getting there but how do to carry more and greater weight of stuff there. Maybe we could make a giant slingshot and slingshot it all there?? Have to have something I suppose to magnetically attract it to the right spot or a good slingshot thrower.


I actually understood all of this. Very interesting subjects. It's amazing this will constantly change and evolve to be more efficient as the programs grow.


I think that the problem with nuclear powered thrust is the weight of the fuel. The whole purpose of interplanetary vehicles (or any vehicle, for that matter) is to carry a payload. Nuclear reactor fuel is heavy. On the McDonnel-Douglas 88 airliner, the landing gear doors had skid pads attached to them in case the doors did not retract during landing. These blocks of metal were made from spent nuclear fuel waste (someone once told me they were spent blocks of plutonium, but I really don't know) and were extremely dense, and really heavy. Compared to nuclear fuel, plasma weighs nothing. And magnetic acceleration has been around for a long time, with the potential to accelerate ions almost to infinity. I don't know, man. Ion powered thrust seems pretty desirable when compared to nuclear powered engines. In our workbook, the link is very interesting.

Cynthia K.

I would like to submit another rocket engine design, and one which I have a personal connection with: Beside Solid, Liquid, and Ion, a fourth type that has been very successfully tested and demonstrated is nuclear. My uncle (now deceased) worked on the Nuclear Engine for Rocket Vehicle Applications (NERVA). NERVA met or exceeded all NASA and DoD design requirements, and was thoroughly tested in Area 21 at the Nevada Test Site, with the Kiwi engines They are throttle able, with a very high Specific impulse power. There are films you can see on You tube of the Kiwi tests. President Kennedy was present for a Kiwi test firing, and was accompanied by my uncle at the test site . If we go to mars, the nuclear engine is likely the best engine to do so. The issue that must be worked out is crew shielding using relatively light weight materials. They have to be shielded from both Gamma and Beta from the reactor. The best approach is chemical or chemical/solid to boost out of the atmosphere and nuclear for the long trip to Mars. Due to its high ISP, the trip to Mars is shortened. I don't think the old fears of firing a rocket with fissile materials which might have to be destroyed by range safety are as valid as they used to be, due to the increased reliability of rockets today. The old days of the Atlas boosters lack of reliability are now far behind us. The nuclear candle would only be lit after TMI (Trans Mars Injection) . I would very much appreciate Cmdr. Hadfields comments/thoughts on this.

Myroslav R.

Maybe it sounds stupid, just trying to figure out how it works. So - in order the spaceship to dock ISS the spaceship needs to overtake the station by going lower orbit, then catch up with it by speeding up, going to higher orbit and slowing down because of that at the same time? Did I get it right?

Maurice Y.

So we just need a new type of power source to give that ion engine some kick. A - Z.P.M.


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....