When Will We Travel Interstellar?

Les Bossinas (Cortez III Service Corp.) [Public domain], via Wikimedia Commons

Les Bossinas (Cortez III Service Corp.) [Public domain], via Wikimedia Commons

Spaceships are cool. But, starships are cooler. I’ve always dreamed of hopping aboard a ship and sailing into the stars, whizzing by nebulae on my tea break, crash-landing on hostile planets, and buying mysterious trinkets at intergalactic bazaars. I want to see humans spread to the stars.

Interstellar travel is the core of space opera and science fiction. Early sci-fi presumed travelling between the stars would be as easy as popping to the shop in your car. But we’ve barely made it off planet: the more we look at it, the harder it seems to get.

Where are my starships?

Interstellar Travel Is Hard

It’s those pesky laws of nature. The basic physics of escaping the gravitational pull of the Sun – it’s hard enough for rockets these days just to escape the Earth. It’s hard enough to get off Earth, we struggle to get people to the moon.

The problem comes down to this: to escape gravity you need fuel (such as rocket fuel), the more fuel you carry, the heavier your rocket is and the more fuel you need to lift it. This is bad enough when getting the Soyuz capsule up to the ISS; most of the rocket is just fuel to carry the fuel to launch the rocket. It’s just ridiculous when you start talking about escaping the gravity of our own sun.

Physicists sling around the term delta-v when talking about this. This comes from something known as the rocket equation. Delta-v is the change in velocity required to escape a gravitational body such as the Earth, Moon or Sun.

How Close Are We To The Stars Now?

VOYAGER 1, nasa [Public domain], via Wikimedia Commons

VOYAGER 1, nasa [Public domain], via Wikimedia Commons

The moon is as close as humans have got. We’ve scattered our robot servants from Mercury, to Mars, to Pluto and beyond (thanks for the photos Cassini). But, have any of our spaceships escaped the gravitational pull of the Sun?

No. Unless you count Voyager 1, the man-made object that has travelled furthest from the Earth. It has achieved escape velocity and is zooming fast enough to overcome the Sun’s gravity. Voyager 1 crossed the heliopause in 2012 – where the solar winds meet the interstellar medium. It’s officially interstellar by some definitions.

Now, it wanders through the Oort Cloud, the sparse shell of icy lumps responsible for long period comets (see Halley’s comet). It will take thousands of years to reach a nearby star, and that’s presuming it’s lucky enough to be on the right trajectory. Its mission continues until 2025 when the last vestiges of power drip away.

Voyager 1’s path out of the solar system, Tom Ruen [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], from Wikimedia Commons

Voyager 1’s path out of the solar system, Tom Ruen [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], from Wikimedia Commons

I wonder what it would be like to be Voyager 1 – to experience the lonely spiral into the interstellar medium. But, that’s probably a speculation for another blog post.

On the 5th November 2018, Voyager 2 joined Voyager 1 and became officially interstellar.

As for humans getting into interstellar space, the outlook is bleaker still. We’ve not even returned to the Moon, let alone got humans to Mars. We’re leagues from getting humans to another star system.

We just don’t have a fuel that gives us enough energy. Even if we worked out how to produce antimatter, even though antimatter-matter annihilation is 100% energy efficient, we would require fuel tanks dwarfing the rest of the craft to have any hope of reaching our stellar neighbours.

We’re going to need to reinvent propulsion, discover new laws of physics or be content stuck in a single star system.

If you’re anything like me, that answer won’t satisfy you. Yes, we know the limits; we know the challenges; we know it’s a distant future. But, we’d be morons if we didn’t give it a good old try.

How Might We Get To The Stars?

Robots like Voyager 1 would be our first pioneers. Perhaps we might send swarms of starwisps or other slow-motion explorers to spread through the cosmos, gather data and test new theories of propulsion. There’s a chance of interplanetary travel such as a Mars or Moon mission – or even the idea of capturing asteroids.

To make getting to the stars easier, we’d first need to make escaping the Earth’s pull easier. For that, we’d probably need to unlock nuclear fusion or build launch assist structures like a space elevator, orbital ring or even the more obscure ‘space mountain’.

With fusion or matter-antimatter annihilation, we may have a hope of powering a ship to the stars. The big problem is propellant. As I mentioned before, the rocket equation can’t be avoided. Like Voyager 1, we might be able to escape the Sun’s gravity well; but, like Voyager 1, it’d take hundreds of thousands of years to reach another star system. So, unless we invent cryogenics or build generation ships, we need to rethink or get better tech.

What Might Make Interstellar Travel Possible?

Kevin Gill from Nashua, NH, United States [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

Kevin Gill from Nashua, NH, United States [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

One commonly touted idea is “lightsails”, or the lesser-known “magsails”. The sails capture the light or magnetised particles from the solar wind and use that to propel them into space. To get interstellar, the sails would have to be giant sails the size of Texas; It would take a long time, but ships such as these, with their age-of-sail feel, would easily reach half of light speed and beyond – fast enough that time would contract with a process known as time dilation – so the journey would feel shorter for the travellers.

Though we’d have to turn the sails round mid journey so we could use the light from the star we want to visit as a break. Man the rigging Mr. Hornblower!

As humanity’s burgeoning space civilisation grows, we might build entire networks of giant lasers that guide and push lightsail spaceships along. We could have a lightrail network (probably with the same extortionate ticket prices of standard rail networks).

With the vast space and time between the stars, human civilisation would be fractured but connected.

Want something bigger than a lightrail network? Have you considered a Shkadov Thruster? I first discovered the concept as a part of Isaac Arthur’s excellent Megastructures series. It’s essentially a half Dyson sphere with mirrors wrapped around the Sun. The light is focused into a laser that pushes the entire star system through space. It also doubles as a weapon.

Now that’s a starship.

What About Faster Than Light Travel?

I know. We’d all like wormholes to be real, we all want the warp drive, we all want hyperspace networks. But the more we look at these options, the more unlikely they become and the more we’d need to play with parts of spacetime we simply don’t understand. It’s an Outside Context Problem.

But, what about the Alcubierre drive you say? That warps the fabric of space, so the spaceship can stand still while moving at faster than light speeds. Perhaps if we got our hands on something known as “negative matter”, a completely different thing to antimatter. It has negative mass (whatever the fuck that means).

And since negative matter would gravitationally repel normal matter, it’s not going to be anywhere nearby for us to mine. To top that off, there’s a chance that the maths for the Alcubierre drive predicts a singularity (read “black hole”) in the middle of the spaceship. So, you might just get crushed into an infinitesimal dot.

Porte des étoiles, Eric Heunthep [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

Porte des étoiles, Eric Heunthep [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

Surely there’s wormholes though. Couldn’t we build a bunch of stargates and send them aboard rockets to further and further stars? I, like you, want to take a shortcut through spacetime and step through onto a forest planet full of suspiciously human-shaped people. It’s called a magic door.

Opening a magic door needs a magic ingredient. You guessed it: our buddy, negative matter. You’d probably need a whole Jupiter’s worth to open the wormhole big enough to get a person through. Have you got a spare Jupiter made of negative matter?

That’s what I thought.

Aha! You say. You’ve not considered hyperspace. We can simply jump into another layer of reality where the laws of nature are different and take shortcuts ignoring the pesky irritations of relativistic travel like time dilation.

Fair point. Sounds like a doddle. Enter a reality where the rules are different from ours? Sure. Them’s godlike powers. I wouldn’t even know where to begin. To paraphrase Orson Scott Card, no-one can even agree what hyperspace is. It’s just a word we use to suspend the laws of reality.

And, if we could do it, we’d probably need a buttload of negative matter.

When Will We Stop Wasting Time And Start Building Starships?

It’s happening. We’ll need a few moonbases, Mars colonies and interplanetary trade routes before we get serious.

Faster than light may be impossible. Building lightsails networks might be a long shot. But more ridiculous things have happened: a few billion years ago, some molecules started replicating, those molecules came to life and became single celled organisms and multicellular organisms: plants and animals. And one of those animals was us. Who went from the caves to the cosmos in less than hundred million years.

Given time, nothing can stop humanity’s upward march. We will own the stars.