Asteroid mining?

Considering that my cities are designed to be enclosed loops, with little interaction with the natural world, they may necessarily need to reach out to other places beyond the Earth to find the resources required for continued existence. I am a big proponent of asteroid mining, as it would provide us with ample resources from throughout our Solar System. With the closed-loop design, the hope is that no contaminants would leak into the natural environment, but that we humans could still get what we needed for our society. The launch loop that I designed would be used to launch our miners into space. Once they have their cargo, in order to return to the surface, they could re-enter like the Shuttle does now, but I would prefer a controlled descent, in order to avoid a Russian meteor-type incident.

Here is the launch loop:

The concept shown needs a large flat area to be built (probably over the prairies). It is 200 km from one end to the other, and reaches a height of 10 km in the centre. It is a shallow-angled arc with an inital angle of less than 10 degrees. A vehicle needs to reach a speed of 11 kilometres per second in order to get into orbit. In this model the craft will be accelerated along the track at a rate of 4 G, (39.2 metres per second squared) or an increase in speed of 140 kph every second. Because this acceleration force can cause some people to black out, safety restraints will of course be used, as well as the option of putting passengers to sleep during launch. Acceleration time will be 5 minutes, covering a distance of 3300 km, most of which will be achieved after the vehicle exits the launcher. The advantage of the launch loop to traditional rockets is that once the vehicle exits this launcher, it will be clear of 99% of the atmosphere, which will drastically reduce the requirement for heat shielding on the craft, cutting down on energy requirements to get the craft moving. Also, while space-faring crafts may still use traditional rocket propulsion to complete acceleration, they need not be. Ion propulsion and other technologies can also be used
to complete acceleration to the speed needed to escape Earth's gravity.