To really get a good understanding of what particular asteroids are made of, the companies will have to send out scouts. Instead of a geologist, they will be remotely operated unmanned spacecraft. Now, until recent history, unmanned exploration spacecraft either did flybys over specific routes, or went to orbit only one space body. After their launch, which gave them the velocity they needed to get to their destination, they only had thrusters to steer themselves and no real main propulsion. DAWN is the first unmanned spacecraft to have its own main propulsion via an ion drive. Now its on its way to Ceres after orbiting and orbiting Vesta. That's what you want in a scout. It needs to orbit several asteroids by jumping from one to another. Ion drives were first tested on NASA's Deep Space 1 mission with a mission manager that felt like Captain Kirk, Marc Rayman. He also manages DAWN.
Marc is a pretty neat guy. After the video interlude, let's get back to our topic. As for finding the needed materials, and impactor and a spectrograph could be a quick way of determining the composition of asteroids or comets. A scout could have several impactors. This would be similar to the Deep Impact mission, but I imagine smaller and simpler impactors would be preferable. Another way is to simply spectrograph the surfaces of the asteroids or comets. I also would imagine marking the asteroids and comets by landing a small radio code transmitters. This would be useful for the miners to come to them and find them. Then on Earth, an automatic ground based system could track them without the need of an astronomer.
|Deep Space 1|
The processing plant should not be on Earth. It should be in a place that is easily accessible from Earth and from deep space. Earth-Moon, or Sun-Earth L2 could be ideal places. The processing plant would be a complex piece of machinery that perhaps would need humans to maintain it when it breaks. Now such a plant would process the ore and have some material left over. The waste material could be either sent to the moon or be collected next to the station, effectively making a ever growing pile of rubble that becomes an asteroid itself.
Now, I've heard an alternate motivation for mining asteroids and that is for precious and rare minerals. Whether such minerals exist in asteroids, I don't know nor have I read anything to that effect. In such a case, bringing such material to Earth would be appropriate. Such minerals could be sold in existing markets.
The use scouts, miners, and processing plants is the heart of my imagined space mining plan. Now this little thought exercise is nice but is by no means the only way. I just laid out a way that I thought would work. It's fun to let you imagination run with a solution. I even thought of an alternative which would make the miner and processor into one vehicle. Yet, every plan will have different benefits and liabilities. I'm sure you can come up with your own space mining operation plan. It's a fun activity.