From the physics of g-force to weightlessness: How it feels to launch into space

What does it take to launch into space?

Other than money, hard work and many moving parts, the answer is science! This summer, NPR science podcast Short Wave is launching Space Camp, a series about all the weird and wonderful things in our universe. We start with how to get to outer space in the first place.

Rockets and Isaac Newton

It mostly goes without saying, but for a person to get to outer space, they need to be in some sort of spacecraft attached to a rocket.

That rocket shoots out exhaust when it leaves the launch pad. That exhaust is shooting towards the launchpad. This is where Isaac Newton's third law of motion comes into action. This law says that "for every action there is an equal and opposite reaction." So, as the exhaust pushes downward, it creates an upward force, letting the rocket shoot skyward.

A good example on a smaller scale is a common physics demonstration where someone holds a fire extinguisher while sitting on something with wheels. Like in this video, as the extinguisher fires, the person goes the opposite direction.

The exhaust from a rocket launching into space does the same thing.

The rocket has to go really fast because it needs to overcome the curvature of spacetime itself. The fabric of our universe, called spacetime, can be thought of as a bendable sheet. The mass of Earth makes the flat fabric of spacetime curve inward in a funnel-like shape. Moving up the funnel — thereby escaping Earth's gravity — is more difficult than moving down.

G-forces and why floating is falling

When those rockets blast off, astronauts experience intense g-forces.

G-forces come from when your body experiences acceleration. When you're just sitting or walking around on Earth, you're probably not noticing them — even though there's always the regular pull of Earth's gravity, which is 1 G.

You're more likely to notice them when you're doing something like going up in an elevator pretty fast. Then, you feel heavier.

But the heaviness of being in a fast elevator is nothing compared to what astronauts experience during a launch. Retired Navy Captain and former NASA astronaut Wendy Lawrence recalled the feeling of intense g-forces to NPR in a recent interview.

"I remember on my first flight thinking, 'Oh, my gosh, somebody just sat down on my chest,'" she says. "I tried to see if I could put my arm out in front of me ... and like, 'Wow, I cannot hold it out there against this tremendous power and acceleration being produced by this amazing space vehicle.'"

Pretty quickly, that experience changes. Once rockets detach from the spaceship, that force pushing the astronauts into their seats is gone. They start to float under their seatbelts.

They feel what is commonly called weightlessness.

But gravity isn't gone. Even on the International Space Station, astronauts experience microgravity.

You can get a small taste of this feeling on Earth. There are amusement park rides that shoot up — causing riders to feel heavy — and then drop riders. During that drop, the riders feel weightless even though they're actually falling. In physics this is called freefall. All the astronauts in the International Space Station are technically falling very slowly, which is why they feel weightless.

Captain Lawrence says it's an amazing experience. "You just relax," she recalls. "You're suspended right there in the middle of the air, and you want park yourself in front of a window and float in front of it and watch the world go by."

To orbit is to fall and miss Earth

It turns out that orbiting, as astronauts aboard the International Space Station do, is falling. Specifically, it's towards Earth.

Newton had a series of thought experiments to explain this idea.

Scenario 1: Imagine you're standing on flat ground. Now imagine that you shoot a cannonball horizontally from your spot on the ground. In this scenario, the cannon ball will travel horizontally for a while before it starts to fall along a curved path. This is projectile motion.

Scenario 2: You shoot this same cannonball horizontally — from the top of a very tall mountain. In this case, the ball would hit the ground even farther away because it had farther to fall and would have been in the air longer. If you shoot the cannonball out at a higher velocity, it would travel even farther. That curved path is getting more and more stretched.

Scenario 3: With a high enough launch speed you can get the cannonball to fall at a curved path that matches the curvature of Earth. Since the curvatures match, the cannon ball keeps missing Earth. This is what it means to have something in orbit. The cannonball falls but never reaches the ground.

Preview of Next Week's Short Wave Space Camp: Pluto

Now if we get out of Earth's orbit and to the end of our solar system, we will pass the beloved once-planet Pluto. Next week we ask: Why are there only 8 planets in our solar system? What does it mean that Pluto was downgraded to a dwarf planet all those years ago? We also explain why Pluto's geology surprised scientists.

Have other space stories you want us to cover? Email us at shortwave@npr.org.

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This episode was produced by Berly McCoy, edited by Rebecca Ramirez and fact checked by Regina Barber, Emily Kwong and Rebecca. Gilly Moon was the audio engineer.