This episode is sponsored by Wren, a  website with a monthly subscription that helps fund projects to  combat the climate crisis.

Click the link in the description to  learn more about how you can make a monthly contribution to support projects  like rainforest protection programs. [♪ INTRO] Since the 1950’s, humanity has gotten  really good at putting stuff up into space. But we haven’t had as much success  at bringing in back down again.

What goes up doesn’t always come  down as fast as we want it to, and we’re now facing the growing problem  of space junk cluttering the skies. But finally, in a long overdue  effort to clean up after ourselves, space researchers are considering  a nifty little accessory called a drag sail that could transform  the life cycles of orbiting stuff. Ever since Sputnik, thousands of  rocket launches have put satellites, space stations, rocket parts, and other  assorted junk into the skies above our planet.

NASA reports that there are about 23,000 chunks  of space junk larger than a softball, half a million pieces larger than a marble, and 100  million fragments one millimeter or more across. All of them are traveling at up  to 28,000 kilometers per hour, so they have a lot of potential to do serious  damage to anything that might get in their way. In fact, with so much going on up there,  scientists have warned of a catastrophic chain reaction of collisions  known as Kessler Syndrome.

In this scenario, one space junk collision  generates more, smaller pieces of space junk. They may be smaller, but they’re  still fast and capable of destruction. So more pieces lead to more space junk  collisions, to more space junk, and so on.

Eventually, low Earth orbit becomes  inhospitable to the stuff we want there, from communications satellites to the ISS. Basically, we drown those orbits in space garbage. A UN report in 2013 projected that catastrophic  space junk collisions might occur at least every nine years, and as we put more stuff  into space, that chance only gets higher.

And it’s not a problem that  will resolve itself easily. Some dead satellites and rocket parts  do drop down low enough to experience atmospheric drag, slow down, and burn up. In fact, eventually all of our  space junk will meet this fate.

Even in orbit, there’s always some drag  from the very top of the atmosphere. But eventually isn’t good enough. Stuff will come down, but in many cases  it’ll take decades, or even longer.

Typical humanity, right?. Pollute space first, think about it later! Well, we’re in the second part now  because more and more engineers are looking for solutions  to the space junk problem.

Many proposals have suggested ways to  deal with the junk that’s already there, like firing lasers from Earth to  change the trajectory of pieces, or sending up trash collection missions  to scoop up as much as possible. These are all… a bit of a challenge to pull off. Whether it’s costs, or  risks, or some other reason, no one has come to a decision about  the best way to dust bust the skies.

But there is a potential solution that  would help avoid making any more space junk, by providing spacecraft with  a way to deorbit much faster. Ironically, these new accessories were  first developed to help spacecraft to fly farther into space,  rather than to bring them home. Solar sails offer an economical  alternative to traditional fuel when it comes to long-term missions  and deep space exploration.

By spreading out huge thin sheets, they  allow spacecraft to fly like a glider, pushed along by the pressure of  photons radiating from the sun. The push is very small, but the force  acting constantly on the solar sail could help it accelerate gradually up to  very high speeds, with no fuel necessary. It’s a technology that’s already been proven too.

Lightsail2 is a spacecraft about  the size of a can of tennis balls, but it’s fitted with a paper-thin  solar sail about 32 meters square. Using nothing but the light from the sun, it’s been cruising around in low Earth  orbit, maintaining its altitude since 2019. Lightsail2 has been the inspiration for  other solar sails on future space missions, but the technology has also inspired an  approach to Earth’s space junk problem.

Because while huge sheet-like  sails are good at catching light, they’re also not picky about what else they scoop. When these sails, with their massive surface  areas, encounter even the thinnest air at the very top of Earth’s atmosphere,  they’ll experience a huge force of drag opposing their flight,  relatively speaking, anyway. In theory, a sail would be enough to rapidly slow  down a spacecraft or satellite, so that it can drop out of orbit quickly and not spend  any more time as space junk than necessary.

So, engineers are looking to incorporate these  drag sails into future satellite flights. Made of a foil that’s just one tenth the  thickness of a human hair, they can vary in size depending on the size of the object  they’re meant to bring down to Earth. The smallest are about three and a half square  meters, and can deploy in just 0.8 seconds, while the largest are about 100 meters  square and take 45 minutes to extend fully.

The bigger the sail, the more  drag, and the faster the descent. The developers believe that this  technology could bring down satellites weighing up to 1500 kilograms! The idea is that the sail would be  stowed throughout an orbiter's mission, but when the mission concluded they  would be released and would unfurl.

After deployment, they’d be completely passive, and wouldn’t need any extra guidance or control. They’d exploit simple aerodynamics to do  their job of bringing the spacecraft home in a blaze of glory! Drag sails have already been tested successfully  on several missions in the last few years, and the European Space Agency are looking to  incorporate the technology into more flights.

Even if we can’t rid ourselves of smothering junk, we may finally have a way of  at least slowing its growth. Who’d have thought that the way to  slow stuff down and bring it home was to use technology we’d developed for  speeding it up and keeping it in space! Both in orbit, and on the  ground, we’re learning more about how to make the future more sustainable.

And you can make a contribution  with today’s sponsor, Wren. Wren is a website where you can  calculate your carbon footprint, then offset it by funding  a wide variety of projects, from community planting trees in Kenya  to mineral weathering in Scotland. All you have to do is answer a few  questions about your lifestyle, then you can sign up to make a monthly  contribution to help offset your carbon footprint.

And they’ll send you monthly  updates so you can see where your money is going and how it’s helping. And we’ve partnered with Wren  to plant 10 additional trees for the first 100 people who  sign up using our referral link! So, you can find that link in the description,  and thank you for supporting SciShow. [♪ OUTRO]