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Saturday, 10 September 2016

Starship drives part 5: Have engine will travel(ish)...

An artist's conception of LightSail - a technology that could be developed into a simple stardrive - in low Earth orbit. Image credit: The Planetary Society
In this post:

A stardive and a destination isn't a space mission, its just the early stages of very fast shower of wreckage. That's because, at starship speeds, even hitting the ultra thin stuff between the stars is like having someone blowtorch your ship's front end (although it's a lot more expensive). But every problem has a solution*...

* Although occasionally it's 'give up'

Starship drives part 5: Have engine will travel(ish).

Ask yourself this: What makes a bullet lethal?

Because, if you look at one sans gun, all you have is a teeny piece of metal. What makes that dangerous? Many handgun calibres you could even swallow without choking - it’s not the bullet that kills, it’s the speed. 

To prove I know stuff and should be trusted on that, here’s an equation*:

K.E. = ½ x M x V x V 

Where K.E. is kinetic energy, M is the objects mass, and V is its velocity.

… and that’s not just any equation - that’s the equation that tells us something’s kinetic energy (how much energy it contains because of its speed). Velocity is in there twice, which means that it’s a much bigger part of the equation than anything else. So if you want something to transfer more energy to a thing it hits (and hence do more damage) it’s easier to pump its energy up with extra speed than extra mass.  

That's how bullets work, and it's also why just pointing a starship at your destination and flooring it will result in a very fast cloud of wreckage: Starships will need to travel very, very fast. Even the slowest of slowboat starship concepts needs speeds of tens of kilometres per second, and any vehicle that could reach another solar system in a human lifetime needs speeds of tens of thousands of kilometres a second. These are speeds that we just don’t encounter on Earth - put simply, our intuitions on what would be dangerous thing to hit are all off.

OK, your intuition is right that hitting a planet would still be bad.

Running into a dust grain barely big enough to see, at say 5% of lightspeed (5% means 80 years travel time to the nearest star), would have a similar effect to a blowtorch being pressed into your starship’s hull. Things get worse as speed climbs up towards light speed – hitting the same dust grain at 99% of lightspeed would cause a significant explosion. 

A TIE fighter wouldn't stand a chance.

Although they usually don't anyway. Sorry Darth.
Even interstellar gas can cause damage, gradually eroding your ship.
So how does a starship captain deal with the danger of space dust and gas? Well, there are a few ideas….

1. Actually push a shield ahead of your ship: 

It’s not going to help with the drag or your fuel efficiency, but a big chunk of ‘dumb matter’ (rock, scrap, the bloated corpses of a space pirates victms… whatever yo have to hand) will keep you ship safe and your crew un-irradiated.

2. Multiple redundancy: 

Don’t just send one ship, send fifty – that’s the philosophy behind the 'starwisp' idea: If you can miniaturise your space ships then you can send a cloud of them, and statistically a couple of them should make it to the other end with enough electronic brains intact to carry out their mission. Not the best idea for crewed ships through, unless you’re truly desperate.

3. Shoot the buggers down: 

This also doesn’t help very much with the radiation problem, but as far as particles large enough to cause macroscopic damage…. You could think about mounting a laser on your starship to shoot them out of the sky. 

4: Use a magnetic shield:

A lot of the particles between the stars carry an electric charge, which means they could be deflected from a starship's path using magnetic fields - Centauri-Dreams takes a look at that idea here.

Not to mention high energy particles zipping about deep space: A hit from a cosmic ray in your computers memory cache could leave the ship thinking it has been built by chickens as a way to strand you in deep space without a helmet.You can shield your computer, but that means extra weight. And those cosmic rays? Not so great for your DNA either.

When it comes to higher performance starship drives - the physically possible but hugely fuel guzzling ones that could get up to nearly light speed - you start to run up against the strange effects of general relativity (a brilliant theory clearly designed to present a huge middle finger to stardrive enthusiasts everywhere). You’ll encounter some seriously weird problems if you manage to get close to light speed like: 

• Time slows to a crawl 
• Distances contract along the direction you’re travelling 
• Your mass increases. 
The starlight becomes lethal gamma rays 

All of the above becoming more-or-less infinitely strong as you get closer to light speed. Why?

So, barring a magical forcefield, and Star Trek style warp drive - oh, hang on, I've got a post right here on just that... 

* Please forgive me, I don't do this often.

** Still want to know? Good, we'll make scientist of you yet. This is a good place to start:

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