Thanks to Skillshare for supporting  this episode of SciShow Space.

The first 1,000 people to click  the link in the description can get a free trial of Skillshare’s Premium Membership. [♪ INTRO]. It’s August 7, 1971, and the Apollo  15 astronauts are on their way home.

They’ve entered the atmosphere,  fired their control thrusters, and the parachutes have just deployed. And then Mission Control tells them  to, “Stand by for a hard impact.” This is not what you want to hear when  you are on your way home from the moon. You want everything optimal.

Things were not optimal. It turns out, one of their  three parachutes didn’t inflate! Fortunately, the other two did inflate and they slowed them down enough  that everyone was fine.

But almost 50 years later in 2019, both SpaceX and Boeing ran into similar problems. SpaceX had three out of four parachutes  on a Dragon capsule fail to inflate, and Boeing had a chute that  just didn’t deploy at all. Parachutes have one job.

Why can’t we get them to do it? Well, it turns out, parachutes are super hard! They’re such a complex, dynamic  physical system that it’s difficult to predict whether  they’ll inflate at all, let alone whether they can stand up to  the forces they experience when they work.

That’s why we’re still trying to understand them more than 500 years after they were invented. So, when we think of parachutes, we usually think of basically  a half-balloon shape. But when Leonardo da Vinci drew  his parachute design in the 1480s, it was a pyramid, and shapes more similar to hang gliders started showing up around 1615.

These designs were all very academic, with maybe a little bit of testing  but no real development or interest. Likely because we, you know,  couldn’t get up very high. Well that changed in the late 1700s,  when hot air balloons were developed.

The first recorded human jump happened  in 1783 from the top of an observatory using a parachute with an internal  frame, so basically a big umbrella. By the early 1800s, engineers had  gotten rid of the frame at the top, and they also added a vent. Now it might not intuitively make sense to  put a hole in the thing that is meant to catch all of the air, but the  vent was actually crucial.

Without it, there was so much turbulence that parachuters were just whipped around in the air. The vent reduced that turbulence and  allowed parachuters to land safely, and presumably without throwing  up all over the spectators. That design from the early 1800s  is basically what we still use now: a frameless balloon shape with  some venting for stability.

But how we use parachutes has changed a lot. They’re not just for landing humans any more. We’re also using them for landing huge machines.

In fact, the first use of a parachute  with a machine was for a racecar. And while that was testing  a design meant for humans, it eventually became clear that the  right size chute could slow even bigger machines, and from there it was a  hop, skip, and a jump to spacecraft. So let’s talk about that application specifically, because this is where things get sticky.

To land a big machine, you need a big parachute. Parachutes work by catching air as they descend, and the pressure from the air creates  a force distribution called load. Load is a function of surface area.

That means a big parachute carrying  a big spacecraft could catch a lot of force when it deploys.  Maybe more than it can handle. So to get around this, engineers  use a dual-deployment system consisting of a drogue chute and a main chute. Drogues have a smaller area, so  they can slow down the craft enough that the main chutes can deploy.

And they have other benefits as well. A dual-deployment system is  what we’ve been using basically the whole time we’ve been going to space. It’s very effective when everything goes to plan!

But things frequently do not go to plan, which brings us back to SpaceX and  Boeing’s parachute-related setbacks. Part of the issue is that when  launching things into space, we want them to be as light as possible. So we’ve been introducing lighter materials.

But we need to test those materials, and  part of how we do that is through models. This, though, presents a couple challenges. One is that it is super hard to model parachutes.

Air behavior can change super fast  as you move through the atmosphere, and turbulence is extremely  hard for computers to model. So any model we’re working with  isn’t going to be very precise. Another thing is that the assumptions  that everyone has been using to make their models have been… wrong.

For like, a long time. Specifically, they were wrong  about how much load the lines that connect the chutes to the  spacecraft would experience. These assumptions are based on  data from the parachutes used in the Apollo missions, and the  mistakes just happened to cancel out, or at least they got close enough.

But when using the same assumptions  with different materials, you get something called  asymmetrical load distribution. Basically, the parachute experiences  different amounts of force over its area so that it can’t really inflate. …which is bad. So both our models and our parachutes  need to be updated and improved, and some of the ways engineers  are doing that are pretty neat.

One line of investigation looks at reefing, where specific parachute lines  that hold the chute closed are strategically cut in order to  control the rate of inflation. Boeing’s parachutes now use extra  strong reefing lines so that they don’t snap too early, and  NASA engineers have developed high-precision accelerometers that  can measure the rate of inflation and be used to test new reefing systems. Meanwhile, SpaceX is starting  to use a material called Zylon, which is basically super nylon,  and a new stitching pattern that reinforces areas of the parachute  expected to get the highest load.

So they’re basically assuming that  asymmetrical loading is going to happen, and then working around it. Meanwhile, computer scientists  are developing models to understand how fabric  behaves on the microscale. That information could be used to  understand how and why parachutes fail, and for developing or modifying synthetic fabrics to get a fabric that is  extra strong and extra light.

So even though we’re still  working with the same basic plan as we used in the 1800s, it turns  out there is still some work to do to bring parachute technology  into the 21st century. If you enjoyed learning about parachutes, you might want to take a dive over to Skillshare, where people learn about all  sorts of fascinating things from physics and astronomy  to painting the night sky. Skillshare is an online community  curated specifically for learning.

If you’d like to keep your feet on the  ground rather than falling from the sky, you might enjoy Indoor Gardening:. Grow Houseplants, Veggies,  and Herbs with Ekta Chaudhary. And there are tons of other courses too!

The first 1,000 people to click  the link in the description can get a one-month free trial of a  Skillshare Premium Membership. And thank you for your support! [♪ OUTRO].