However helium 3 requires that you first have working commercial aneutronic nuclear fusion. Even in my more optimistic assessment that is not until the 2020s. Earth can get billions of tons of rare earth materials off the ocean bottom (recent Japan find) or can get uranium from the ocean (Japan can do it for about $150 per pound, there is 4 billion tons in the ocean).
The true larger industries for space :
Information and satellite servicing
There is already a tourism market of tens of millions of dollars for space. However it has been a handful of billionaires paying $20 million at a pop. There will be a few thousands of people flying Virgin Galactic and other suborbital flights. 430 have signed up for $200,000 a piece.
It costs $70,000 to 100,000 to climb Everest. 4000 or so have tried. The Seven summits costs $200,000. Thousands of people per year go on mountaineering and ocean expeditions that are quite expensive.
International tourism receipts grew to US$919 billion (euro 693 billion) in 2010.
Spacex and Bigelow Aerospace (and european competitors) could open up the orbital tourism market. Say $500k-5million per traveler. It could become a multi-billion market in the 2020s.
Information and satellite servicing
If NASA and other agencies outsource the gathering of information.
The information and TV produced from cheaper satellites and cheaper launch could become independent industries.
With new nanosat manufacturing and Spacex and those that follow Spacex it is possible that are far more dynamic private space satellites could emerge.make a more precise nanosat GPS network. New entrants could displace and grow known established markets for communication, information etc… NASA could pay for a science mission to asteroids say someone using solar electric sail propulsion.
Global 2010 revenues for the satellite industry totaled $168.1 billion, for an 11.2 percent average annual industry growth rate over the past 5 years.
It is a few billion dollar market if you have space tugs and fuel depots to keep expensive satellites from falling out of orbit.
You could more cheaply take water and materials from the moon to produce or support satellites for earth.
Having robotic rovers on the moon, Mars and other places and transmitting digital RED camera super high definition. Could create live 3D virtual exploration. There have already been the IMAX shuttle, Hubble space movies.
Colonize and make true space economy
Live and stay. Mine and generate energy and build for a true space based economy. What were the economics for the North American colonies. Sure they sent back furs and fish and other things to the Old world, but the true economy became the people and what they did there. United States, Canada, Mexico. Build lunar cities, Build cities on Mars. Colonize Asteroids. Mine the moon for uranium and produce nuclear Orion ships and go anywhere in the solar system. Do not have to worry about fallout getting in the magnetosphere of the Earth. Earth can get billions of tons of rare earth materials off the ocean bottom (recent Japan find) or can get uranium from the ocean (Japan can do it for about $150 per pound, there is 4 billion tons in the ocean). It will take decades but when you have hundreds of millions of people in space and staying there that will be the big payoff. It requires a long term vision beyond a decade.
About 20,000 commercial jets move hundreds of millions of passengers every year. Space planes can be built. Skylon could work and that would have a crude version able to hold a hundred people at a time or at least like a large business jet able to hold 20-50. Move up from the few thousand people per year of the $50,000 to 200,000 level (the tourism case that I already made) $209 billion was spent on the space shuttle and over $100 billion on the International Space station. A level of commitment of that scale would obviously enable a true opening of space if it was properly applied. Several technologies could be tried for lowering the cost of getting to space below $100/kg. Colonization efforts could be seeded and nutured – if there were coordinated plans.
The goal beyond that is Kardashev Level 2. If we stay on Earth we will be limited to about Kardashev level one. Kardashev level 2 is 4 billion times more energy. If we stay on Earth, it is like those who lived on only one Pacific island and never left. They can build up the one island all they want but it would not be able to match an economy with ten thousand islands. On Earth you could have a few Quadrillion economy but with the solar system it would be a Billion Quadrillion (Septillions). In the 1500s, Portugal, France, England and Spain had far smaller economies than China. The United States, Canada and Mexico were a far bigger payoff set of projects than anything that China built from the 1500s to the 1800s.
All of our weapons now will proliferate and we will have more powerful ones in the future. Spreading out across the solar system and then beyond will be safer. How safe would it be if you had a few hundred people on an island with everyone with AK47s and grenades ? The US has a problem with guns and weapons but those weapons and conflicts does not put civilization at risk. The similar situation is scaled to the Earth and solar system with nuclear weapons and beyond.
The weapons that we have now and that we can project will not put a nuclear fusion, fully space capable civilization at risk. We can try to convince people to play nice but we cannot have that as the sole option. If by spreading out we are safer that is what we should do. Peoples minds cannot be expected to be transformed into a peaceful utopia but it is perfectly feasible to build and spread out and have overall safety even if people remain flawed.