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Did you know rockets have to reach 40,000 kilometers per hour? just to break free from Earth's pull?
What?
That's 40 times faster than a jet.
Hello friends and welcome back to Sleep Tight Science a bedtime show that answers your questions about science.
We're continuing our Making and Creating series, where we explore how people build and engineer amazing things, from chocolate bars to machines that can leave the planet.
Tonight's topic was suggested by Ravid, who is eight years old.
Thank you for your questions about space and rockets, Ravid.
In this episode, we are going to try and answer the following question.
How do rockets work?
What makes them powerful enough to escape Earth's gravity and travel to space?
We'll start with the challenge.
Why leaving Earth is so hard.
Gravity pulls everything down.
The atmosphere creates resistance. and you need to go incredibly fast just to break free.
Then we'll explore the solution how rockets work by pushing gas at one end to push themselves the other direction, and why they carry their own oxygen.
Finally, we'll look at the engineering how rockets are built in stages that separate and fall apart, and how engineers test every part to make sure it works.
You don't have to remember every word or every concept we share.
It takes time to understand new things, and sometimes the science we share has big words and ideas.
It's okay.
Try to remember this.
Rockets work by pushing hot gas out the bottom very fast, which pushes the rocket up.
Engineers have to build them strong enough, light enough and powerful enough to reach the incredible speeds needed to escape Earth's pull.
Before we continue, Here are some words to listen for.
Gravity, the force that pulls everything toward Earth's center.
Thrust, the pushing force that lifts a rocket.
Propellant, rocket fuel, includes both the fuel that burns and the oxidizer that provides oxygen.
Combustion, burning fuel to create hot, expanding gas.
Stages, sections of a rocket that separate and fall away as fuel is used up.
Escape velocity the speed needed to break free from Earth's gravity about 40000 kilometers per hour or 25000 miles per hour.
A quiet thank you to Etta and Arlo Paquin, age nine and seven, in Minnesota, for introducing our show.
And to all our wonderful friends who send in questions.
You help us learn together.
And thank you to all our listeners.
Without you, we couldn't make this show.
Take a great big belly breath and imagine this.
A rocket stands on a launch pad, tall and sleek, filled with fuel.
Engines ignite.
Flames and gas explode downward.
The force builds, pushing, pushing, until slowly the rocket lifts.
Gravity pulls down, but thrust pushes up.
The rocket rises faster and faster, climbing towards space.
Ready to explore how humans engineered machines powerful enough to leave Earth?
Let's get started.
Leaving Earth is hard.
Really hard.
And to understand why rockets are built the way they are, you need to understand the challenge engineers faced.
The first challenge is gravity.
Earth pulls everything toward its center.
That pull is what keeps you on the ground, what makes things fall when you drop them.
If you want to leave Earth and go to space, you have to go fast enough that Earth's gravity can't pull you back down.
That speed is called escape velocity.
And for Earth, it's about 40,000 kilometers per hour, or 25,000 miles per hour.
That's a pretty big number.
So to put that in perspective, A car on a highway might go 100 kilometers an hour or 60 miles an hour.
A commercial jet flies at about 900 kilometers per hour or 560 miles per hour.
A rocket needs to go more than 40 times faster than a jet just to escape Earth's pull.
That's super fast.
The second challenge is the atmosphere.
For the first 100 kilometers or 60 miles or so, you're pushing through air.
Air creates drag, which is friction that slows you down.
The faster you go, the more drag pushes back.
This friction also creates heat, which is why rockets glow during launch.
Rockets have to be streamlined, smooth sides, pointed nose to cut through air as efficiently as possible.
The third challenge is that you need continuous power.
A rocket can't just get a running start and coast.
Gravity is always pulling, always slowing you down.
You need engines pushing continuously until you reach the right speed and altitude.
Only then can you turn off the engines and coast.
And here's the tricky part.
Fuel is heavy.
The more fuel you carry, the heavier your rocket is.
The heavier you are, the more fuel you need to lift all that weight.
Engineers had to find clever ways to solve this problem, and we'll see how in the next part.
So if you decided to make a rocket tomorrow, your challenge would be this.
You would need to reach 40000 plus kilometers per hour, push through the atmosphere, carry enough fuel to do all of that and don't make the rocket so heavy that it can't lift itself.
Humans have been dreaming about reaching space for a long time.
The Chinese invented gunpowder rockets over a thousand years ago for fireworks and weapons, but those couldn't reach space.
In the early 1900s, scientists like Konstantin Selkovsky, Robert Goddard and Hermann Oberth worked out the math and science of how rockets could actually get there.
The first object to reach space was a German V-2 rocket in 1944.
In 1957, the Soviet Union launched Sputnik, the first satellite to orbit Earth.
In 1961, Yuri Gagarin became the first human in space.
And in 1969, NASA's Apollo 11 landed astronauts on the moon.
It took decades of work, thousands of engineers and a lot of testing.
Sometimes rockets exploded on test stands or broke apart during flight, but each failure taught engineers what needed to be fixed.
That's how progress happens test learn improve, test again.
In the next part we'll look at the solution, how rockets actually work and the clever science behind getting them off the ground and into space.
So, How do rockets solve the challenge of leaving Earth?
It starts with a simple principle discovered by Isaac Newton over 300 years ago.
Newton's third law of motion.
It says, for every action, there is an equal and opposite reaction.
What does that mean?
Push something one way, and you get pushed the other way.
When you jump off a boat, you push the boat backward and yourself forward.
When you blow up a balloon and let it go, air rushes out one end and the balloon flies the other direction.
Rockets work exactly the same way.
Push gas out the bottom very fast and the rocket gets pushed up.
The pushing force that lifts a rocket is called thrust.
To create thrust, rockets burn fuel.
Burning fuel creates hot gas that expands rapidly and shoots out the bottom of the rocket through a nozzle at incredibly high speeds several kilometers per second.
The force of all that gas rushing out pushes the rocket in the opposite direction.
Up.
But here's a question you might be wondering.
There's no air in space.
Fire needs oxygen to burn.
So how do rockets burn fuel in space?
The answer is that rockets carry their own oxygen.
On Earth, engines in cars and airplanes get oxygen from the air around them.
But rockets can't rely on that, because once they leave the atmosphere, there's no air.
So rocket fuel comes in two parts.
The fuel itself, the thing that burns, like kerosene or liquid hydrogen, and the oxidizer which provides the oxygen, usually liquid oxygen.
Together, these are called propellants.
When they mix and ignite in the rocket's combustion chamber, they burn extremely hot, hotter than lava, and create expanding gas that shoots out the nozzle.
There are two main types of rocket fuel.
Liquid fuel is stored in separate tanks and pumped into the engine.
It's very powerful and can be controlled.
You can turn it on, turn it off, or adjust the flow to change how much thrust you're creating.
Most modern rockets like SpaceX Falcon 9 or NASA's Space Launch System use liquid fuel.
Solid fuel is different.
The fuel and oxidizer are premixed into a solid form, like a giant, powerful firecracker.
Once you light it, it burns until it's gone.
You can't turn it off or adjust it.
Solid fuel is simpler to build and store, but less flexible.
The space shuttle used two large solid rocket boosters on the sides of the main fuel tank.
Now, remember the problem we talked about earlier.
Fuel is heavy and carrying fuel makes you heavier, which means you need more fuel.
Engineers solved this with a brilliant idea rocket stages.
A rocket is built in sections, stages stacked on top of each other.
Each stage has its own engines and fuel tanks.
The bottom stage, stage one, is the biggest and most powerful.
It lifts the entire rocket off the ground.
After it burns through its fuel, usually in just a few minutes, it separates and falls away.
Now the rocket is lighter.
Stage 2 fires and keeps accelerating.
When Stage 2 runs out of fuel, it separates too.
If there's a stage three, it gives the final push to reach orbital speed or head beyond Earth.
By dropping empty stages, the rocket gets lighter as it climbs.
Less weight means you need less fuel to keep accelerating.
It's far more efficient than carrying all that empty metal to space.
The Saturn V rocket that carried astronauts to the moon is a perfect example.
It had three stages.
Stage one had five massive engines and burned for about 25 minutes, lifting the rocket to 61 kilometers or 38 miles.
Stage two burned for six minutes. taking it to 185 kilometers, or 115 miles.
Stage 3 burned twice, once to reach orbit around the Earth, and again later to send the astronauts toward the Moon.
By the time they reached the Moon, about 90% of the rocket's original weight had been left behind.
Rockets also need to steer.
They do this by tilting the direction their engines push.
Some rockets have movable nozzles that can tilt slightly.
Some use small side thrusters.
In space where there's no air resistance, even a tiny push in one direction can change your course.
Tomorrow, you might think about the elegant solution engineers invented.
Carrying your own oxygen, dropping weight as you go, steering by tilting thrust.
Here's what you can notice about rockets and how they're built.
Watch a rocket launch if you get the chance.
You can find videos online or, if you're lucky, see one in person.
Notice how slowly it lifts off at first.
It takes time to build speed against gravity's pull.
Notice the bright exhaust trailing below.
That's superheated gas shooting out at an incredible speed.
If you watch closely, you might see stages, separate pieces, falling away as the rocket climbs and gets lighter.
Think about the engineering challenge A rocket has to be light enough to lift itself but strong enough not to collapse or explode under the forces of launch.
Fuel tanks are surprisingly thin, like a soda can, but they hold thousands of liters of super cold liquid fuel.
Every part is tested repeatedly because rockets are expensive and dangerous, so engineers check everything.
Rockets in Museums.
If you ever visit a space museum, notice how huge rockets are often as tall as a 30-story building.
Notice the engines at the bottom, with large bell-shaped nozzles where gas shoots out.
Notice how the rocket is divided into sections.
Those are the stages that separate during flight.
Tomorrow, at breakfast or at dinner or with your friends, you might talk about what it would feel like to ride in a rocket, or how engineers figured out how to make something powerful enough to escape Earth's gravity.
So back to Ravid's question.
Rockets work by burning fuel and oxidizer together to create hot gas that shoots out the bottom at extremely high speed.
That pushing force, thrust, lifts the rocket up.
To escape Earth's gravity, rockets must reach about 40000 kilometers per hour, so they're built in stages that drop away as fuel is used, making the rocket lighter and faster.
Engineers design every part to be strong, light, and powerful enough to reach space.
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In this episode, we learned how rockets work.
We discovered that leaving Earth is hard because gravity pulls everything down, and to escape it you need to reach about 40000 kilometers per hour, more than 40 times faster than a jet.
We learned that rockets work by Newton's third law push hot gas out the bottom very fast and the rocket gets pushed up.
We found out that rockets carry both fuel and oxidizer so they can burn in space where there's no air, and that they're built in stages that separate and fall away to make the rocket lighter as it climbs.
Engineers spent decades testing, learning from explosions and failures, until they finally built machines powerful enough to reach space.
Take a slow, deep breath in and let it out gently.
Maybe tonight you'll dream of climbing into a rocket, strapping in, feeling the seat beneath you.
The countdown begins.
Ten, nine, eight.
Your heart beats with the numbers.
Three, two, one.
Engines ignite below, a deep, chest-shaking roar.
The whole rocket trembles, then slowly you lift.
Gravity pulls you down into your seat, but thrust pushes harder.
You rise faster, faster, punching through clouds, the sky turning from blue to black.
Perhaps you'll feel the first stage separate beneath you a sudden jolt, then silence for a heartbeat, before the next engine fires and acceleration pins you back again.
You're lighter now, climbing faster.
The curve of Earth appears below, blue and white and impossibly beautiful.
You could float weightless in the cabin after the engines cut off, looking out the window at the planet shrinking below.
Continents drift past, The sun rises every 90 minutes.
Stars don't twinkle up here.
They shine steady and bright in the black.
Maybe you'll ride in the cockpit during re-entry, feeling the atmosphere grab hold, watching orange and pink flames streak past the windows as friction slows you down.
Or you might become the rocket itself a stage separating, tumbling back through thin air engines, firing one last time to land upright on a platform ready to fly again.
You could stand on the moon looking back at Earth, a blue marble hanging in the darkness, knowing that a rocket brought you here across 380000 kilometers of empty space.
Your imagination can take you from launch pad to orbit and beyond.
Thank you for spending this time with us.
From Cheryl and Clark, good night, sleep tight.
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