[♪ INTRO] We’ve probably all had that tragic experience of losing a balloon as it floats up into the sky.

But sometimes we want balloons up there. Like, way up there.

In space. Because balloons, for all their round, innocent floatiness, can be really helpful for space science. So here are 5 uses for balloons in space that really pop.

Satelloons of NASA’s project Echo Before satellites were floating boxes with solar panel wings, they were balloons. In the late 1950s, NASA engineers were working on a sate-lloon of sorts called Project Echo. The Echo satellite was something like a giant metallic birthday balloon the width of three school buses capable of holding more than 18 thousand kilograms of air inside.

Originally, researchers wanted to use the balloon to measure how dense the air in the upper atmosphere is, so that they could design more efficient aircraft and spacecraft. But it ended up essentially being a guinea pig for future satellite communication instead. See, back then the world depended on a massive network of under-sea cables and microwave transmitters to send phone or TV signals from one place to another.

But those systems could only send so much information at a time, and demand was starting to grow beyond what the system could handle. So engineers at Bell Laboratories suggested that instead of cables, we should bounce transmissions from one point on the globe to another using satellites. And thanks to this big shiny balloon, engineers were able to show it was possible.

On August 12, 1960, Echo was shot into space. A few hours later, it relayed a message from President Eisenhower from a ground station in the deserts of California to Bell Labs in New Jersey. And in the weeks that followed, it bounced telephone messages and eventually even a live television broadcast.

Now, these transmissions were passive, meaning radio signals would hit the sate-lloon and, like a kid running full tilt at an exercise ball, they would just bounce right back off again. That was possible because the sate-lloon skin was made of super thin layers of aluminum foil and plastic. That made iit not only super shiny but also extra tough to withstand pressure, temperature, and meteor punctures.

But the Echo project wasn’t without its hiccups. As balloons are sometimes known to do, an early version of Echo popped as it was inflating up in space and ended up as a spectacular fireworks show. But with some extra calculating and tinkering, Echo ended up carrying out its scientific missions.

And it paved the way for other impressive science-y space balloons. Like in 1996, when NASA launched an inflatable antenna experiment aboard the shuttle Endeavor. This antenna was the size of a tennis court, some 14 meters across, making it visible from Earth.

It kind of looked like a massive, puffed up pop socket with struts connecting to a measurement system. But this blow-up science experiment wasn’t your ordinary party balloon. One half of the antenna was made from a heavy-duty plastic called Mylar, the same stuff lots of coffee or food packaging is made from.

And the other, reflecty side was made from Mylar infused with aluminum. Much like the Echo sate-lloon, this antenna was tasked with showing that even more precise inflatable space antennas were possible. See, Echo’s bulbous shape meant that the incoming radio waves spread out when they bounced off.

So several stations received a little bit of the reflected signal, but no-one got a really good signal. The inflatable antenna aboard Endeavor, on the other hand, had a much more typical dish shape, so it could focus those incoming signals better. And a more focused signal would mean better telecommunication.

And one of the best parts is that scientists didn’t need to get a massive, rigid, heavy dish on board a space shuttle and then launch it up into orbit. The inflatable antenna, along with its collapsible struts, inflation system and measurement system folded down to a package the size of a desk, making it relatively easy and cheap to launch and deploy. Now, the inflatable antenna was never actually used to transmit signals, but making and sending the antenna up into space showed that it was possible to unfurl more complex inflatable structures up there.

Pretty soon engineers were finding all sorts of uses for balloons in space, and taking those balloons further afield too. Shortly after the inflatable antenna experiment, another set of balloons was sent all the way to Mars. These were the airbags surrounding the Pathfinder lander and the Sojourner rover.

The rover’s mission was to collect data about what Mars’s rocks and soils were made of, take pictures of the surface, and measure the red planet’s atmosphere. But to do that, it had to get to the surface in the first place. Now, NASA had landed on Mars before, but those previous missions had relied on rockets to fire and slow the lander down before it reached the surface.

Which is fine, except that the fuel from those rockets could contaminate the soil. And if your mission is to analyze the elements in that soil, then rockets weren’t such a stellar idea. So instead, engineers decided to surround the lander on all sides with 24 human-sized airbags and drop it with a parachute.

The total balloon bouquet was almost the size of a giraffe in every direction. Each balloon was made from a tough, spacesuit-like fabric called Vectran, built to resist popping when the balloons touched down on the jagged Mars surface. Several of the initial balloon designs didn’t survive the testing phase.

But after a redesign, engineers built Pathfinder’s airbag balloons from multiple, thin layers of Vectran rather than a single thick one. The outer layer acted as a buffer against any rocks so that the inner layer holding all the air was protected. Which all added up to the airbags’ success on the red planet.

And ok, so the airbags themselves weren’t doing the science per se. But without these balloon clusters, the rover that was studying the surface of Mars may never have made it to its planetary lab in the first place. Following that success, scientists were eager to take the whole balloons-on-Mars thing even further.

Instead of just surrounding a rover with balloons for a landing, researchers thought… why not make the entire thing inflatable? See, researchers want to be able to study large sections of the Martian terrain, but most of the planet is made up of steep cliffs and jagged rocks. That makes it tough going for even the most adventurous and high tech of dune buggies.

So to get around, or rather over, this issue, NASA engineers in the early 2000s came up with a concept for an inflatable Mars rover based on a tumbleweed. They figured if the balloon was big and light enough, it could easily roll over obstacles and propel itself with just a light wind. If you’ve ever tried to chase a massive beach ball that got away from you, you’ll understand the concept!

Here’s how it works: Any scientific instruments, say something for measuring magnetic fields or detecting water, are suspended by cords at the center of the balloon. Those instruments are surrounded on all sides by one giant, 6-meter-wide balloon made of the same material as the Pathfinder airbags. On opposite sides of the balloon are two weights that help the tumbleweed roll in a relatively straight line, since the balloon will tend to roll with the heaviest part down.

Once the rover reaches a spot researchers think is interesting, the balloon can be deflated to stop it from rolling away and the scientific instruments can get to work. And when it’s time to get the ball rolling again, you just inflate the ball! Engineers calculated that, on Mars, a 20 kilogram ball could travel at up to 10 meters per second, even uphill.

And the tumbleweed ball isn’t the only concept for an inflatable rover. Another version looks similar to a cartoon tricycle with oversized wheels, and could theoretically cover 99% of Mars’s terrain. And a group of Swedish scientists have proposed a beach-balloon rover to tumble alongside other, more complex vehicles.

Some researchers have even proposed taking the tumbleweed ball to explore other windy terrain like Neptune’s moon, Triton and Jupiter’s moon, Io. Now none have been built yet, but I’d like to encourage engineers to consider the entertainment potential of a bouncing, tumbling rover and get on it. The last item on our list takes the idea of space balloons to the extreme.

Not only is it the biggest balloon on this list, but it doesn’t even need gas to keep it inflated. I’m talking about an interplanetary blimp, also called a vacuum airship. This 80 meter wide craft could float over rugged Martian terrain, the watery planes of Saturn’s moon Titan or the violent volcanic surface of Venus.

Unlike regular balloons, a vacuum airship has a rigid outer structure and is filled with, well, a lack of air… a vacuum. It needs that rigid structure to keep it from collapsing under the pressure of the atmosphere. See, ships or balloons float because they displace, or push away, the air around them with something less dense.

Technically, a vacuum has a very tiny density; somewhere in the range of 6.5 times ten to the minus twenty-seventh power kilograms per meter cubed. Take my word for it… that’s not much. So vacuum balloons could theoretically work on Earth, since the vacuum inside is less dense than the air around it.

The problem is, the pressure of our atmosphere pushes back on the balloon, and no amount of support structure would be enough to keep it from collapsing. But with the right design, these balloons might just work on other worlds, like Mars. Engineers have proposed a space blimp design with an inner shell that contains the vacuum, connected to a lattice of lightweight but rigid beams that make up the outer shell which stops the balloon from buckling..

Plus, it doesn’t hurt that the Martian atmosphere is about 160 times less pressurized than Earth’s is. Which means the vacuum balloon wouldn’t have to withstand such crushing atmospheric pressures. And the reason space blimps are so appealing to scientists is that they’re really energy-efficient.

For one thing, the vacuum airship wouldn’t need to carry any extra gas for refueling, meaning it can carry more important stuff like scientific instruments. And it wouldn’t need any massive engines like planes on earth do, since all the lift comes from its air-deprived core. But maybe the best reason scientists are trying to build space blimps is that surveying a planet or moon from on high means you can cover wide areas, fast.

Basically, you’re not having to fight your way over rocks and hills, and you can see more of the landscape at a time. Wildest of all, the vacuum airship was actually first imagined way back in the 17th century! Yet, four centuries later, we still don’t have a prototype airship.

But both NASA and the European Space Agency are investigating whether it's feasible. Balloons in space may seem too whimsical to be taken seriously. But with what engineers have learned so far, it’s clear that with some experimentation and proper materials, it’s possible for these ideas to really take off.

And I guess we were feeling a little whimsical when we made this episode, so we decided to turn it into a bunch of stickers. Because that seventeenth century vacuum airship was too good to pass up, so we made this extremely fun and floaty sticker sheet! And that’s not all.

The month of April is almost over, and that means your time is almost up to pre-order this month’s rocket-themed SciShow Pin of the Month before it flies away forever… like a balloon drifting into the sky. Like all of our monthly pins, this one’s a pre-order and we’ll stop taking orders and start filling them as soon as the month ends. But we’ve got another great pin coming up next month, so you can look forward to seeing that.

To get your sticker sheet or your pin, you can get started at dftba.com or check out the links in the description, and thank you for watching. [♪ OUTRO]