Science & Tech

Rockets: Orbital Mechanics

Chris Hadfield

Lesson time 23:51 min

Chris uses familiar situations—like driving a car and jumping off a diving board—to illustrate how the laws of orbital mechanics govern spaceflight and navigation

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

Topics include: Launch Site Logic • How to Change Orbits • Changing Orbits With the Hohmann Transfer • Orbital Velocity vs. Escape Velocity • Perceived Weightlessness • Newton’s Law of Universal Gravitation


The first human being to ever leave the earth was, of course, Yuri Gagarin. And then the next was Al Shepard, and then Gus Grissom, and onto eventually John Glenn orbiting the world as well. And they launched from two specific places. Yuri launched from Baikonur, Kazakhstan and the Americans launched from Florida from Cape Canaveral and what became the Kennedy Space Center. So why did they choose those places on board this globe? And it's actually sort of a question of physics. The world, of course, turns. It spins around on its axis once every 24 hours. And at the equator , the world, it's about 24,000 miles around or 25,000, and it goes around in 24 hours. So that's nice, easy math. If you're standing on the equator, you're 24,000 or 25,000 miles around, and you go around 24 hours. You're going about 1,000 miles an hour if you think about it. If you're standing on the equator, you are going 1,000 miles an hour to the east just by standing there. If you're on the North Pole, you're not going anywhere. You're just standing there, and the world sort of turns underneath you. So if you're a rocket designer, you want to get that 1,000 miles an hour for free if you can. So you want to launch as close to the equator as you possibly can. And that's why the Russians got as far south as they could down here into Baikonur right into Kazakhstan so that they could launch and take advantage of the rotation of the Earth. Politics didn't let them go any further south. The Americans did the same thing. They launched as far south down on the east coast as they could, because they're going east. And they launched down here on what became the Kennedy Space Center in Florida for the same reason. Since then, we've built launch sites closer-- even in Brazil has built one on the equator. And we actually have portable launch sites that sometimes get on a barge and get on a launch from the equator just to steal as much of that Earth's rotation as possible. Because every bit of spin you get from the Earth is one less kilogram of fuel that you need to put in your rocket. Sometimes, though, you want to launch into a different orbit for a scientific purpose. Let's say you want to map the whole world and have it turn underneath you. It would be kind of nice if your satellite was orbiting around the world from north pole to south pole, because then the whole world would turn underneath you. If you just launch east out of Florida, then you won't go any further north than Florida or no further south than that as you're orbiting around the equator of the world, and you'll never see the north or the south. And so sometimes, we launch rockets rather than taking advantage of the spin of the Earth, and we launch them straight south or straight north. And then they end up in an orbit. Even though it may not take advantage of the Earth's spin, it does put us in an orbit that serves the purposes of that rocket launch. I like holding a globe. It reminds me of act...

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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Chris Hadfield

The former commander of the International Space Station teaches you the science of space exploration and what the future holds.

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