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The physics of launching into space -- and crashing back down

JUANA SUMMERS, HOST:

Now is an exciting time for space exploration. NASA has approved missions to the moons of Jupiter and sent a probe to touch the sun. SpaceX wants to one day put people on Mars. That could fundamentally change our relationship with space as we know it, and Short Wave, NPR's science podcast, wants listeners to be ready. Their series, Space Camp, is a journey through a changing universe combining basic physics with the latest science research. Host Emily Kwong starts with the physics of launch, how to send something up and how it can come crashing back down.

EMILY KWONG, BYLINE: Navy captain and NASA astronaut Wendy Lawrence is very familiar with going into orbit. Her first launch was in 1995 on the space shuttle Endeavour. Once the rocket reached space, that's when the fun really began.

WENDY LAWRENCE: It's just awesome. You're just perfectly suspended right in the middle of the air and watch the world go by.

KWONG: While it feels like astronauts are floating, in physics terms, they are actually falling very slowly back to Earth. Think about the Tower of Terror in Disneyland.

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KWONG: You feel weightless for that moment when you drop, even though you are actually falling. In physics, we call that free fall, and it all starts with projectile motion. Here's Wendy again.

LAWRENCE: I think pretty much every kid has thrown a ball. Gravity pulls it eventually back down to Earth, so, you know, that ball kind of has an arc shape as it travels. So in general, that's happening to my spacecraft. It literally is falling back to Earth.

KWONG: Isaac Newton described orbit through this thought experiment. Imagine a cannon aimed horizontally. If you were to shoot the cannonball, it would travel for a while, then start to fall in this curved path. Now imagine this cannon was on top of a giant mountain so high and the launch was so strong that the cannonball's curved path matched the curvature of the Earth so that it kept missing the planet, never hitting the ground because the cannonball was moving that fast. That is orbit.

But things in orbit don't always stay there. Take space junk. Low Earth orbit is becoming a junk yard for orbital debris generated from satellite collisions and stuff that just breaks down, falls apart and occasionally falls back down to Earth.

LAWRENCE: Even a fleck of paint off an old satellite can do damage because we're talking about a tremendous rate of speed to stay in orbit. The space station right now is probably going 5 miles a second, 8 kilometers a second to stay in orbit - same with the orbital debris. So it doesn't have to have a high amount of mass to do a lot of damage.

KWONG: There are over 45,000 objects in space that we know of. Most of it is nonoperational. It's just junk. Earth's gravity can pull a piece of junk back into the atmosphere over time. The vast majority of it burns up or falls into the ocean, but not always. In 2019, a pseudo satellite launched by Samsung fell on a farm in Michigan. Nancy Welke posted about it on Facebook.

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NANCY WELKE: This baby fell out of the sky and landed in our yard.

KWONG: Then, in March of this year, part of an old battery pallet from the International Space Station pierced the roof of a home in Naples, Fla. Currently, there is no international treaty that limits space junk nor sets standards for negligence if a country creates more. Astrodynamicist Moriba Jah wants to see space become a much more sustainable place.

MORIBA JAH: Countries, governments need to incentivize their industry to say, you're going to get some kind of incentive or tax cut or whatever if you design, build and operate reusable and recyclable satellites.

KWONG: But until that future comes to pass, we're going to see more things in orbit, yes, but also more space junk littering the sky.

Emily Kwong, NPR News.

SUMMERS: Special thanks to our friends at the U.S. Space and Rocket Center, home of Space Camp.

(SOUNDBITE OF T C LONG'S "UNIVERSAL SPIRALS") Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

Emily Kwong (she/her) is the reporter for NPR's daily science podcast, Short Wave. The podcast explores new discoveries, everyday mysteries and the science behind the headlines — all in about 10 minutes, Monday through Friday.