Space colonization will only be viable if we are able to launch stuff into outer space at reasonable cost. Currently spaceflight depends on chemical rockets to reach orbit. However, chemical rockets suffer from a severe bottleneck.
Since the fuel of a chemical rockets serves as both propellant and as the source of energy, the exhaust velocity of the rocket’s reaction mass is restricted by the energy content of the fuel. Put simply: the higher this exhaust velocity, the less propellant we need to launch a certain payload into orbit.
Chemical rockets that are used to launched satellites into outer space from Earth, contain up to 80 to 90 percent of their total mass of fuel, with the remaining reserved for payload. This also explains why spaceflight is so expensive: you need a lot of fuel to launch relatively little payload.
The principal alternative for chemical rockets as a method for launching stuff into space from Earth are thermal rockets. Unlike chemical rockets, they use an external energy source to heat up a certain propellant. The main benefit of this propulsion method, is that the propellant can reach arbitrary temperatures and hence velocities.
One design of thermal rockets has been proposed by the late Jordin Kare and his idea is to use Earth based laser to heat up a propellant such as liquid hydrogen in a rocket. This system is illustrated below:
The Kare launch system has some benefits. First of all, the power source stays on Earth, so we do not need to spend energy to lift that into space along side the payload. Also many of the components already exists or could be developed at relatively short notice.
On the other hand, the use of power laser beams will conflict with aviation. So if this launch system, adequate coordination with air control authorities will be essential. Possibly it should be built in remote locations such as North Queensland.
Needless to say, the laser units will require a lot of energy. For environmental reasons we would prefer to use solar and wind power as much as possible. This choice, however, requires some kind of energy storage system to manage any fluctuations in supply and smooth out the peaks of demand.
One idea to store energy is to use flywheels as is shown in the video below:
Jordin Kare estimated the cost of his launch system to be between 2.5 and 10 billion USD. Let’s that considering inflation and cost overruns 25 billion USD would be a more realistic figure. This is, of course, a large sum of money but if institutions like ESA and JAXA are serious about getting to the Moon, funding this project should not be a real issue.
Once such a space launch facility has been established, additional revenue could be raised through the launch of commercial satellites. This would then be used to fiance the next stage: building a space habitat in Equatorial Low Earth Orbit.