PBS Space Time | 5 REAL Possibilities for Interstellar Travel | Season 2 | Episode 4

The future of humanity is in the stars.

If we wanted it badly enough, interstellar travel could be achievable in our lifetime.

So what would it take to build a starship?

Why don't we see evidence of galactic empires?

Is our galaxy littered with the remains of single planet civilizations as Elon Musk has asked?

Is it really so difficult to colonize other star systems?

Recently, there's been some pretty wild talk of some crazy ideas for space travel technologies.

We have the non-momentum conserving Em-Drive, the Wormhole from Interstellar, and the Alcubierre Warp Drive.

That last one is extra cool and yeah, we'll get to it.

But let me be clear.

Humanity's first adventure to the stars won't and shouldn't wait for far-off fantastical technologies.

Our first starship would use technologies achievable in our lifetimes.

I'm being optimistic but not unrealistic.

Now building a starship is going to take a huge amount of political cooperation, money, and single-minded focus.

Hell, this thing is so big we're going to have to assemble it in space.

So for argument's sake, let's say humanity's future is at stake, and we just discovered Earth 2.0 in the Alpha Centauri system.

It's only 4.4 light years away, but we have to get there before the Curbles and the impending K1 asteroid that's on its way.

So we have to focus on one design, our best chance.

What do we build?

The key is finding the right balance between speed of the starship and the amount of time it would take us to develop the tech to build it.

No point in launching a slow ship in 20 years if the ship we launch in 50 years overtakes it.

This balance is factored into something we call the Wait Calculation, and we want to get this right.

First, option one.

Traditional rocket fuel.

This is a non-starter, but just to give you an idea, the fastest manned vehicle ever was the Apollo 10 rocket, which reached a speed of nearly 25,000 miles per hour, which would get you to Alpha Cen in nearly 120,000 years.

Uh, no.

Propellant is the big limiting challenge with space travel.

Conservation of momentum sucks.

To learn more, there's some very serious rocket science in this episode about farts.

The rocket equation tells us that maximum speed is based on exhaust velocity, fuel mass, and spacecraft mass.

If you want to get to Alpha Cen in a human lifetime, you need to get to 10% the speed of light.

And to do that with any liquid rocket fuel, you'd need a fuel tank larger than the observable universe.

Not too efficient.

But there are two ways to achieve high velocities, propel a lot of mass backwards or propel less mass at much higher speeds.

So, yeah.

Let's do the second one.

We just want the fuel with maximum energy density.

So direct conversion of rest mass into energy seems like the way to go.

Remember E equals MC squared.

The sun does this pretty well, so let's build an engine that works like a mini star.

I'm talking option two, fusion.

In fact why not choose the most middle option and just explode nukes behind our starship and surf the blasts.

This was a real option considered for the Orion project by Freeman Dyson and others in the late '50s and '60s.

We're going to assume modern thermonuclear devices and launch with roughly 3/4 of our starship's mass being taken up by 300,000 1 megaton hydrogen bombs, blast them behind us one by one over about a month, and we accelerate at 1G to around 10% of the speed of light.

Nice.

We get to Alpha Cen in 44 years, assuming we don't need to slow down at the other end.

Actually, slowing down is a huge issue.

We need to use half of our fuel to slow down at the other end, which unfortunately means we half our speed.

So let's make that 90 years for a one-way trip.

This means we'd need three generations of humans on board that ship and pray that space babies turn out OK.

Still, this tech is perhaps the most achievable in the shortest time.

We already know how to build bombs.

Yay, cold war!

Although the 1963 test ban treaty says no space nukes, maybe we can make an exception for the future of humanity.

There are also some pretty awesome options to running contained thermonuclear reactions on board.

Fusion rockets, either pulse blasts like the Daedalus project or ongoing fusion.

You could push to a bit higher than .1C this way but probably not a lot higher.

It's an awesome option and may actually happen, but the tech for contained fusion is only now emerging, and there are many difficult challenges.

It's rocket science and nuclear physics, so you know, hard.

But fusion turns less than 1% of rest mass into energy.

What if we could get close to 100%?

Well, that's the idea behind option three, antimatter drives.

When matter meets it's antimatter counterpart, both particles are annihilated, liberating most of the rest mass as energy.

This is an extremely efficient fuel.

For example, it would only take around 10 grams of antimatter to fly us to Mars in a month.

The big obstacle here is that harvesting and storing antimatter is incredibly difficult.

We can make in particle accelerators but it's slow and hellishly expensive.

We've only been able to do this with small numbers of antiprotons at a time, not the kilograms we'd need to get to the stars.

Assuming we can scale up production of antiprotons by a factor of say 100 trillion, trillion, then pion rockets may be a possibility.

Annihilate a proton and an antiproton, and you get charged pions moving at near light speed.

Channeled with magnetic fields, these pions provide our thrust.

That's something like 50 times more energy per kilogram of fuel than the best fusion options.

Low fuel weight means our max speed is limited only by how much antimatter we can make.

0.5C is plausible, meaning a trip to Alpha Cen would take nine years.

It may even be possible to push 0.8C, which would be nice, because then time dilation really kicks in, bringing travel time down to 3.3 years from the astronaut's perspective.

OK, rockets a cool and all.

But what if we didn't have to carry any propellant at all?

What if we could sail to the stars on a wind made of light, the light sail?

I'm talking about a kilometer wide sapphire coated sail, riding the beam of a gigantic space laser blasting the power equivalent of 100 nuclear plants.

What the hell, let's do that.

OK, most of the interstellar thinking for light sails has been about unmanned probes.

10% light speed is pretty reasonable with modern materials like a carbon web sail driven by a microwave beam running on a single nuclear power plant.

This is an update to Robert Forward's Star Wisp spacecraft, but it should be scalable.

If we want to take actual humans, we're going to need to a bigger boat, which means a proper visible light laser and a larger sail, coated with advanced, reflective and heat resistant materials like sapphire.

This laser is going to have to be ridiculously large, possibly built on the moon and powered by massive Helium 3 reactors or in orbit around the sun powered by vast solar panels.

How fast does this thing go?

Because we aren't carrying any fuel, maximum speed is only limited by the power and collamation of our laser and the size of our sail.

The longer the effective range of the beam, the higher the speed we can reach.

10% light speed or higher should be doable.

These tech issues need to be factored into the Wait Calculation.

And besides these, slowing down at the other end is a major problem.

There are possibilities for breaking in the stellar wind of our destination star, although that is tricky.

Ultimately, though, the scalability of the light sail means that speeds even greater than .1C are possible.

OK most awesome option for last, the Blackhole Drive, in fact, a Schwarzschild Kugelblitz.

This is an engine powered by an artificial black hole and is one of the fastest options for subluminal travel.

This is a black hole made not from mass but from light.

A sufficient energy density of laser light focused in a small enough region would bend the fabric of space time enough to produce a singularity, the Kugelblitz, German for ball lightning.

A black hole of the right size radiates Hawking radiation like crazy.

The smaller the black hole, the more radiation, and this radiation could drive our starship.

The sweet spot is a black hole of around 600 billion kilograms or two Empire State buildings, which would be roughly the size of a single proton.

Such a black hole would radiate nearly 160 petawatts, which is roughly the equivalent of 10,000 times the world power consumption.

And it would evaporate in around 3 and 1/2 years.

Any smaller and it evaporates too quickly.

Larger and it radiates too weakly and becomes too massive to feasibly accelerate the ship and the black hole.

Assuming we can catch most of the radiation, this amount of power accelerates us to .1C in 20 days and presumably to a significant fraction of the speed of light in the lifespan of the black hole.

There's no question that it ultimately goes faster than the other options.

It's also clearly the coolest of all the subluminal engines.

I mean, even the Romulans use it.

The only drawback is that the lasers creating the black hole would need to be vastly more powerful than even the black hole they created.

This is a possible yet very distant technology.

OK, so lots of ways to get to the stars.

What's the fastest?

Honestly, if we had to colonize in the absolute shortest possible time, then it's nukes, like the Orion project.

We have the tech.

We just have to increase the world's nuclear arsenal by a factor of 200, which we shouldn't do unless it's a question of extinction.

Still, in a super optimistic estimate, we could have boots on the ground in 2120 or so.

Now fusion engines are more sustainable, even if the tech is a minimum of 50 years away.

They land us on Alpha Cen in the latter half of the 2100s, assuming we start now.

Pure antimatter and the Kugelblitz drives, they're the starships of the far future.

Assuming warp drives don't pan out, these are what we'll want to actually explore the galaxy with near light speeds dilating apparent travel time down to human scales.

Let's talk near-term reality.

I'm going to come out and say it.

Light sails.

We'll put our first unmanned probes in the Alpha-Cen system.

It'll take around 45 years from launch, not slowing down at the other end.

And another four and a half years to get the message that we succeeded.

Maybe we could launch a Star Wisp in less than 30 years.

And some kids watching this video might see this to fruition.

Manned light jammers are way off but totally plausible.

Humanity's first attempts to land on other worlds might well have us sailing to the stars.

It's likely between this and pulsed fusion drives.

Either way, pretty epic.

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