Resources from Near Earth Objects
Near Earth Objects (NEOs) are a collection of comets, asteroids and some other objects within the orbit of Mars. Most of these objects regularly come within close range from the Earth, some of those objects are actually easier to reach than the Moon. This seems strange, but in space travel access is not measured in distance but in velocity increments (delta V), which is a measure of the required energy. Because of the Moon’s mass it takes more energy to get to the Moon. And if we want to leave, we have to overcome the Lunar escape velocity.
In order to reach the Near Earth Objects, we have only to overcome a relatively small change in our position relative to the Sun. (Delta V is related to the local escape velocity from the Sun, which is a function of the distance from the Sun.) Therefore we need a rather small delta V to get to the Near Earth Objects. Of course the actual required velocity increment depends on the exact position of a particular object, but since there are several thousands of them we will simply pick one which is relatively close.
The major advantage of NEOs as a mining site, is that they contain a broad variety of resources. Unlike the Moon NEOs contain all chemical elements needed for a modern industrial society. And since NEOs have a negligible gravity, only a modest amount of fuel is required to return resources to Earth or anywhere else in space.
In situ resource utilization (ISRU) is the use of extraterrestrial resources at or near the location where they are mined. ISRU is opposed to importing resources from our planet. One example: the American space company Bigelow Aerospace has designed and built inflatable space stations. Suppose we buy one and we launch it to, say, L4. There we inflate the structure with air, which we have extracted from a Near Earth Asteroid. This example show the benefits of ISRU, by using air from NEO resources we can reduce the payload we need to launch from Earth. Basically we should restrict ourselves to launch only those items which cannot (already) produced in space, in order to reduce launch costs.
The extraction of resources from NEOs, is also important in funding space colonization. Especially the (limited) export of the precious platinum group metals will an important source of revenue for Space communities. The prospect of for-profit asteroid mining also makes it possible to do space colonization without government funding.
After some time, when space based industries are more developed we need to import less from Earth, since more products are manufactured locally. One development which is of interest of space colonization is 3D printing. This technology is also called rapid prototype technology or desktop manufacturing. 3D printing makes it possible to produce complicated structures in short time without a large workforce. Once a structure is stored in a computer file it can be printed on demand. Of course this technology has its limitations, but the prospects are quite promising.