Everyone knows that rockets are huge, expensive, complicated and impractical. Everyone knows that rockets use ridiculous amount of fuel.
Ok. Challenging concept time:
The underlying costs of space travel are not much more than that of air travel. Space travel is 'cheap'; or atleast it will be.
First, rockets need a lot of fuel. The amount of fuel is determined by the rocket equation.
If you plug in the figures into the rocket equation you find that for every pound of rocket, you need maybe 20x that mass of fuel! And in fact, typical modern-day rockets manage nearer to 50x that. That's outrageous; it's obvious where the cost goes right?
But it turns out that fuel is cheap. For example Liquid oxygen (LOX) and Kerosene, LOX is pennies per pound, aviation fuel (kerosene) isn't much more expensive and you need a lot less mass of that than you do LOX, because LOX is pretty heavy. The propellent only costs a few tens of dollars per pound of rocket max.
Therefore if we can get to the point where the fuel is the only thing we need to use up, a 140 lb (70kg) person can get launched for just a few tens of thousand of dollars- hardly any more than the cost of an airflight; a little bit more than a supersonic airflight.
So the fuel is too cheap to be relevant. Let's look at the rocket itself. Here we get into more costs.
The costs of the rocket come from 3 main areas:
- development costs
- buying the rocket
- ground support
Development costs- these add to the price divided proportionally to how often you launch. The more you launch, the cheaper it gets. (That's one thing that went wrong with the space shuttle- they weren't able to launch as much as they'd hope and so it's turned out really expensive.)
Paying for the rocket- Right now of course much of the rocket is thrown away each time (expendable launchers - ELVs) so you need to build a new one each time (except for the Space Shuttle's orbiter which is so expensive it might as well be.) Now, there are several designs such as the ROTON concept that are fully reusable; and there is no known reason why they wouldn't work. The point is that each time you reuse a vehicle, the cost of the vehicle goes down. Now metalwork is much more expensive than fuel, thousands of dollars per kilogram is the normal rule of thumb, but if you can use a vehicle 1000 times then it only cost you 1/1000 of that per launch; so expensive hardware becomes cheap. This is the RLV approach. It seems very likely, but it isn't necessarily true that this will be cheaper. For example, to make a rocket reusable, the rocket needs to be built more heavily. This cuts into the payload mass; and so pushes up the cost per kilogram of the rocket. For example if the RLV were to be only reusable 10 times but costs 15x more than ELVs then it would cost more; in fact the breakeven seems to be around 10x-15x reusability.
ELVs get cheaper too the more you make them, because of production line techniques meaning that the cost goes down as you increase quantities.
Ground support- looking beyond the launcher itself you find many other costs, launch pad, control ground crew etc. However most of these also scale well with launch rate- you launch twice as often and the costs certainly aren't double, nothing like. The ground support costs for the Space Shuttle come to about 2/3 of the cost per mission.
So let's assume you launch a LOT to bring the costs down.
Right now it looks like doubling the rate of launch can almost halve the cost. The underlying per trip costs (fuel mainly) are relatively small, and mass production reduces the cost of even expendable launchers.
The asymptotic cost of getting into orbit seems to be way down around $50/kg, but we are very, very far from that at present.