(electronic beeping) (gentle electronic music) - Imagine taking an elevator to space.

Ideas like this are not purely science fiction.

Engineers are actually working on developing these.

Why?

Because we might be approaching the limit of what our chemically-powered rockets can do.

(upbeat electronic music) Rockets are incredible, awe-inspiring feats of engineering.

They launched about 2,500 satellites into space in 2022 and 2023.

SpaceX alone launched a rocket about every four days in 2023.

- [Person] Two, one.

- [Person] Ignition, and liftoff.

- But rockets are also super-expensive, burn massive amounts of fuel, and when things go wrong, they can lead to disaster.

(explosion booming) And if you look at the physics of what requires them to launch, they are also kind of inefficient, and here's why.

Today, most rockets are powered by chemical reactions.

They rely on combinations like liquid hydrogen, LH2, and liquid oxygen, LOX, or rocket-grade kerosene, RP-1.

These rockets have to carry their own fuel, and they need a lot of it to get to space, which adds mass to the rocket.

In chemically-powered rockets, 80% to 90% of the rocket's mass is just the fuel, and you might think, to go farther into space, you'd just need to carry more fuel, but it's not that simple.

The more fuel you bring on board, the more massive the rocket, and the bigger the rocket, the more fuel you need to get off the ground and escape Earth's gravity.

You can see the frustrating relationship in the rocket equation.

This ratio is the limiting factor.

It's the mass of the rockets fully fueled over the mass of it when it was empty.

During the Apollo program, the Saturn V rocket had a mass ratio of 23.

This means that a fully-fueled Saturn V rocket was 23 times more massive than when all its fuel was used up.

Now, there have been advances in chemically-powered rockets since then, though, like SpaceX's Falcon 9.

Part of that rocket separates from the rest and lands back on a landing pad after launching cargo into space, making it the first reusable rocket.

Before that innovation, most rockets that made it to orbit were either destroyed or not recovered at all.

This Falcon 9 rocket has a mass ratio anywhere between 18 to 30 depending on the mission, but even though the ratio might seem low, at liftoff, most of that is still fuel.

- [Person] There it goes, there it goes, there it goes, oh, my gosh.

(rocket roaring) Imagine how much more cargo or scientific equipment we could send into space if the fuel didn't take up so much room, or better yet, if we use less fuel, or none at all.

So some engineers are investigating other methods of space travel, which brings us to space elevators.

The physics could actually work, but there are some challenges.

In theory, a very long cable would extend from the Earth's equator into space, anchored by some type of counterweight at the other end, like an asteroid or a satellite.

The whole structure would rotate with the Earth, and cargo would be hauled up and down without the need for rockets.

But how would the cable stay taught?

A combination of gravity and centrifugal forces.

The counterweight at that far end of the cable would need to orbit in sync with the Earth, and for that to happen, the counterweight would need to be far enough away that the centrifugal force is greater than the gravitational pull of the Earth.

That would happen at about 22,236 miles away from Earth, and if the Earthly end were located in the ocean, it could potentially be moved around to avoid bad weather or space debris.

But one big issue is the material the cable would be made with.

It would need to be built with something super-strong, able to withstand Earth's gravitational forces, atmospheric changes, weather, and potential collisions with space debris, but it also needs to be lightweight, and nothing like this currently exists yet.

But structures called carbon nano-tubes are being explored as a potential material for the tether for their incredible strength.

But don't count rockets out just yet.

NASA is developing engines powered by nuclear fission to send astronauts to Mars!

Nuclear-powered rockets would be more efficient for long-distance space travel, requiring less fuel and allowing faster speeds.

But these engines come with challenges including harmful radiation, high heat production, and complex, costly designs.

(gentle electronic music) From space elevators to nuclear engines, the future of space travel might look very different from the rocket launches we're used to.

Maybe one day, chemical rockets will be a thing of the past, and we'll be launching into space in ways we never imagined.

(gentle electronic music) So what do you think?

Could the future of space travel be rocket-less?

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