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Environment

Outside/In[box]: How sustainable is space travel?

50410171581_861b32ea87_k.jpg
Patrick Black
/
NASA
Antares Rocket Launch Oct. 2, 2020

Every other Friday on Morning Edition, the Outside/In team answers a question from a listener about the natural world. This week, we encounter a question about space. Jazmine Castro-Diaz asked on Instagram:

“What does the future of space travel look like in terms of environmental sustainability? Like fuel, effects of launches, et cetera?”

When SpaceX or Blue Origin launches a rocket, you can’t help but notice the massive plumes of fire and smoke that get belched out of the bottom of the rocket. But when we talk about the big contributors to climate change, we tend to focus on fossil fuels, cars and planes… even methane emissions from cows get more attention than space travel.

And that’s for good reason.

“IT’S THE PARTICLES, STUPID”

According to Dr. Martin Ross, a scientist with the Aerospace Corporation, a typical rocket launch burns about the same amount of fuel that a day-long flight across the globe burns. But CO2 emissions from airplanes (per kilogram of fuel burned) are seven times greater than rockets. Plus, there’s just way fewer launches than there are flights to begin with. If you add it all up, the rocket industry burns just 0.001% of the kerosene that the aviation industry burns.

But Ross says there is something to be concerned about.

“We don't care about a rocket's carbon footprint. That's irrelevant. It's the particles, “ Ross says. “Remember the old saying, it's the particles stupid.”

If you haven’t heard this exact phrase, you’re not alone. But if you lived through the ‘90s, you may remember the political slogan it’s derived from: “It’s the economy, stupid."

Plume of smoke from NASA space shuttle launch
Trey Ratcliff (CC BY-NC-SA 2.0)
/
https://bit.ly/3wdluAg
Plume of smoke from a NASA space shuttle launch

Regardless of how you want to phrase it, the point is that a rocket engine emits hundreds of times more soot particles than a jet engine per kilogram of kerosene burned. It emits those particles while traveling towards space, and even after it’s reached orbit that material can still re-enter the atmosphere and burn up, where it turns into even more soot particles. And those little bits of burnt fuel are collecting high up in the stratosphere.

“These particles scatter and absorb sunlight. They change the temperature and circulation of the stratosphere,” Ross says.

Whereas a lot of the pollution that winds up in the troposphere (that’s where most of the clouds are) eventually gets rained out, we don’t know too much about soot particles that get trapped higher up. Pollution in the stratosphere is so new, Ross says, we don’t have the data or models to predict exactly what consequences it might have.

So are there good alternatives? Ross says hydrogen could make for a better, cleaner rocket fuel, but the technology isn’t quite there yet because of the extremely low temperature required to fuel a rocket with liquid hydrogen.

That said, there are some other pretty wild ideas that could help lower emissions from rocket launches.

COULD WE SPIN OUR WAY TO ORBIT?

If you were looking to lower emissions from rocket engines, you might think about trying to increase their efficiency or filter the particles or something. But why not just try and do away with the rocket engine altogether?

The company Spinlaunch is aiming to revolutionize satellite launches by basically hucking rockets into space using centrifugal force, at up to seven times the speed of sound.

They’ve got a slick video that shows how this might work in practice, and you can see a small rocket being attached to what looks like a gigantic fan blade, which is housed in a big chamber that sits at a steep angle and is pointed towards the sky.

The blades start to spin incredibly fast, and then at exactly the right millisecond the spinning fan blade releases the rocket and it’s hurled into space.

Once the rocket is high enough, an actual engine will fire for a brief time to achieve orbit, but if all goes to plan the cost and emissions of launching satellites could go way down.

The video is CGI, but the company did do a practice test of a smaller, suborbital system in 2021.

NO SILVER BULLETS TO SPACE

Whatever space technologies we dream up in the future, there’s always the possibility that lowering the barriers to space travel will actually increase net emissions.

This effect is sometimes referred to as Jevon’s paradox, which basically states that consumption increases when the cost goes down and efficiency goes up.

And we may be already seeing that in action – after all, reusable rocketry has dramatically lowered the financial burden of launching rockets, which is at least partially why the number of rockets being launched per year has more than doubled in the past decade.

But if we’re going to be hurling things up into space, we might as well come up with cleaner ways of doing it anyway, right?

If you’ve got a question about the natural world, send it as a voice memo to outsidein@nhpr.org, leave a voicemail on our hotline at 1-844-GO-OTTER, or share it with us on Twitter or Instagram.

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