Airlocks and Reality

 Hi Guys,

Bit of a pet peeve of mine, which I thought I'd let loose. (Sometimes you just see the same thing too many times and you just have to say something.) For me it's airlocks. I've been watching a whole bunch of sci fi / space opera shows lately, (even though I should be writing!) and I don't know how many times I've seen it but people keep getting blown out of airlocks. I hate that! It drives me nuts! It's just so wrong!

There's a couple of reasons for that. The first is of course the design of airlocks which has a single overwhelming priority - keeping the air inside the ship. Air is absolutely the most precious resource a space ship can have, and it can never be wasted. Which means that every airlock in a space ship has a single operational principle - the outer hatch will not open if there's air in the airlock. If it did every time one opened the ship would lose air.

So the way they actually operate, is that you get into the air lock, both hatches are closed, and then the air is pumped out of the airlock, before the outer hatch is opened.

It works exactly the opposite way on submarines where the water is trying to get in. The airlock is emptied before you can open the inner hatch. If it wasn't, then every time you opened the inner hatch, you'd be hit by a wall of water. 

Of course there's a physics issue too. In order to blow someone out of an airlock, you need a pretty good blast of wind. But unless the inner hatch is open as well - in which case all of the ship's air is escaping to space and everyone's dying - it's not happening. The airlock itself is only a small space within the ship - lets say eight cubic metres - or a two by two by two cube. The hatch has to allow people in and out so it's probably the same size as a door in your home, say two square metres. So if all the air rushes out in one second when the door opens, the jet stream hurling the guy out is blasting at a rate of two metres per second for that second or four and a half miles an hour. Which means that only if the man inside was standing right at the outer hatch and got hit by all the air escaping the airlock, would he have to face a full second of this tiny breeze. But most likely if he was up against the inner hatch, banging away frantically as they do in so many films, he wouldn't get hit by any rush of air at all.

You could of course speed up the rush of air by decreasing the size of the outer hatch - rather like making air fly faster by blowing through a straw. But there are limits to how fast the air can fly, and even if all the air smashed into the chest of the trapped man, there would still be no more air mass hitting him than before. And worse, even if for a second that faster moving eight cubic metres of air at one atmosphere dislodged him, he wouldn't go very far. The outer hatch would be so much smaller to achieve this, that he would hit it and get stuck!

So airlocks are a pet peeve of mine - as are killer storms on Mars which has an atmosphere only one percent as dense as that of Earth. Even thousand mile an hour winds would be no worse than someone blowing on you on Earth. And ray guns making noises in space where there's no sound.

My point here is that space operas like all genres, needs to follow some basic physics rules and you can't just write things because they sound cool. And I say that as someone who isn't even a hard science fiction writer. So my thought for writers of sci fi when they're plotting is to add another question to their plotting process - "is this possible?"

Anyway, enough griping. I should get back to writing. After all I am busy working on three books at once! But the good news is that Chy is almost done and hopefully in another month or so it'll be out.

Cheers, Greg.