[♪ INTRO].

A lot of our ideas about the future come from popular works of science fiction, like how the Star Trek communicators of the 1960s became the cell phones of the ‘90s. But go back to the 1800s and some of the most important stories about space travel had nothing to do with rockets, like you’d think they should.

Instead, authors like Jules Verne and H. G. Wells thought we’d get things into space with… guns.

Really big guns. If you think about it, it makes a lot of sense. Things need to go very fast to reach space, and bullets are very fast.

So, voila! Unfortunately... the physics don’t really work that way. But that definitely hasn’t stopped us from trying to build space guns of our own.

Obviously, guns differ from rockets in a bunch of important ways. They’re an example of what’s called ballistic flight, which means that, once a projectile’s launched, only external forces like gravity and drag can affect its trajectory. Guns are an advanced form of creating ballistic flight, but the basic idea goes back to the days of things like trebuchets and, you know, just, like, throwing rocks.

All of that is different than something like a rocket, which can be steered in flight. What guns have going for them, though, is simplicity. We’ve been using the same basic design for hundreds of years and, by now, we understand pretty well how to build something efficient and reliable.

They’re also pretty cheap, since you get to reuse the barrel and just replace the propellant, like gunpowder, after each shot. Still, guns do have some major downsides as a launch tool. To get to space, you need to go really, really fast, and the payload in a gun just gets one shove to get it going that quickly.

So the acceleration experienced is incredible. We’re talking about thousands of times more g forces, or thousands of times the regular force of Earth’s gravity, than when riding on a rocket. Which is not great if you’re an astronaut who suddenly doesn’t have a skeleton.

Reaching those speeds so quickly also really heats things up, meaning your payload needs to be basically fireproof. The real kicker, though, is all the pesky physics. At the end of the day, it’s actually impossible to fire something from the surface directly into orbit around the Earth.

See, you can think of an orbit like a closed loop around the planet. If you fire a projectile from the surface, that loop is guaranteed to intersect the Earth, meaning your projectile will crash into the ground. Meanwhile, after a rocket launches, it fires its engines to creates a new loop, and an orbit, that doesn’t intersect with the surface.

Because they don’t have a propulsion system of their own, ballistic projectiles just can’t do that. Of course, none of this has actually stopped us from building enormous guns to try it out. Because, pff, who needs science?

In the 1960s, Project Harp, or the High Altitude Research Program, was our first attempt to reach space with a gun. The U. S. military was racing to improve early intercontinental ballistic missiles, and they needed a cost-effective way to test how designs reentered the atmosphere.

With Project HARP, they aimed to reuse the leftover barrels of battleship cannons to launch payloads high into the sky. These massive guns were eventually built in Arizona and Barbados, and they were used to fire more than 200 payloads, each weighing about 180 kilograms. At peak efficiency, a HARP gun launched one of these objects at more than 2100 meters per second, fast enough to reach an altitude of about 180 kilometers.

That’s about the same height as Alan Shepard’s historic Mercury mission and is definitely into space. But that gun also had a heck of a kick. The payload experienced around 25,000 g’s at launch, so its electronics had to be encased in solid plastic blocks to avoid breaking apart.

Unsurprisingly, it wasn’t a sustainable idea, but these guns did help us study the Earth’s upper atmosphere, so it wasn’t a complete waste. Some tests released objects that left smoke trails and that helped scientists track the movement of high-altitude air currents. After that, the space gun idea was continued in California in the ‘80s with Project SHARP, or Super HARP.

The regular HARP guns used gunpowder, but Project SHARP was a light gas gun, meaning it propelled objects using hydrogen compressed by a piston. Its goal was to launch small projectiles into space, for real this time, but the projectiles only got about a quarter of the velocity they needed. Still, that was good enough for them to plan the final version, which would’ve had a barrel about 3.5 kilometers long.

Unfortunately, the planned gun cost more than a billion dollars and was never approved. And, although some companies have tried to resurrect the idea over the years, we never really got serious about trying again. With enough money, determination, and propulsion systems, maybe someday we could build a functioning space gun.

But all told, ballistic flight just hasn’t proven to be an effective way to get to space, and its opportunity might be gone forever. The great promise of a space gun has always been that it launches things cheaply, but with the advent of reusable rockets like SpaceX’s Falcon 9, even that advantage is disappearing. Modern rockets can carry more stuff, do more kinds of missions, and offer a gentle ride to space, all without breaking the bank.

So space guns might be out. But hey, we’ll never stop shooting for the stars. Thanks for watching this episode of SciShow Space!

Over the years, people have thought up all kinds of wacky ways to get to outer space, including space guns and even giant elevators. And believe it or not, we’ve looked at the science behind that one, too. You can learn all about space elevators, and whether they’d work, over at the main SciShow channel. [♪ OUTRO].