Resources within the solar system are mind-blowingly huge both in terms of energy and matter. There are planets, many moons and uncountable asteroids and comets.
In space the sun is always shining and there is no atmosphere to attenuates it glare. Solar power is the obvious way to go in, at least in the inner solar system. Either photo-voltaic for electrical power or solar furnaces for material processing.
Creating habitable places for people to live in this ultimately harsh environment is a matter of engineering – see advanced automation.
Creating large space habitats requires the kind of technology described in the section on advanced automation
There are many places that we could locate these habitats, especially near Earth.
Leaving earth with the right attitude
If mankind colonises space enabled by a programme based upon free and open-source-style collaboration, it would be an iconic example for future generations living away from Earth, in terms of encouraging co-operation and resource sharing. These human-centric principles may help reduce the chances of purely self-serving forms of commercialism being dominant in their culture and might lessen the likelihood of conflicts arising from aggressive, exclusionist groups that might otherwise be more common.
If we do successfully colonise space, it is likely that eventually more of humanity will exist off the Earth than on it, so helping to set the right tone for these future colonies is a significant issue.
We now have access to space using rockets although this is still expensive (over $5000 per pound of material launched) and the failure rate is quite high. This severely limits what we can do in space; it is the main obstacle to space solar power and the colonisation of space. So far, we have only dipped our toes, if we want to really dive in we have to make spaceflight cheap and reliable.
It may be that using abundant solar energy and seawater and advanced automation, mature rocket technologies like liquid-fuelled rockets actually end up becoming cheap and common-place, perhaps in conjunction with solid-rocket boosters like the Space Shuttle uses that employ metal fuels and inorganic oxidizers made from common elements.
single-stage-to-orbit (SSTO) hybrid air-breathing/rocket space-plane designed to carry 40 tonnes of cargo or 40 passengers to low earth orbit
However many alternative and interesting launch systems are thought to be technically (or at least theoretically) feasible ranging from single stage to orbit hybrid air-breathing/rocket space-planes (SSTOs), electromagnetic and balloon platform launch assist to more exotic space fountains, launch loops and geosynchronous space elevators. It may be that launch strategies that can have their power systems decoupled from the propellant/propulsion systems and installed on the ground may end up being more economical and efficient in terms of energy expended per unit weight lofted into space.
Information on these alternative launch methods are covered in more detail in this WP article .
Gratuitous image of the Orion Nebula
John young - space is a dangerous business but so is staying on earth (find actual words!)
Is Earth's surface really place for...
The first question which you will ask and which I must try to answer is this, "What is the use of climbing Mount Everest?" and my answer must at once be, "It is no use." There is not the slightest prospect of any gain whatsoever. Oh, we may learn a little about the behavior of the human body at high altitudes, and possibly medical men may turn our observation to some account for the purposes of aviation. But otherwise nothing will come of it. We shall not bring back a single bit of gold or silver, not a gem, nor any coal or iron. We shall not find a single foot of earth that can be planted with crops to raise food. It's no use.
So, if you cannot understand that there is something in man which responds to the challenge of this mountain and goes out to meet it, that the struggle is the struggle of life itself upward and forever upward, then you won't see why we go. What we get from this adventure is just sheer joy. And joy is, after all, the end of life. We do not live to eat and make money. We eat and make money to be able to enjoy life. That is what life means and what life is for.