According to the proponents of asteroid mining, these space rocks are a virtual El Dorado in the sky with more obtainable minerals in the largest three in our solar system than on the entire Earth. The question is, where exactly is all this mineral wealth and how do you get it without going broke in the process?

There's something of an international race to the asteroids underway at the moment, with countries from the United States to Luxembourg backing missions. On the surface it seems like a two-tier race – NASA and ESA are sending giant spacecraft and even manned missions, while private firms are concentrating on tiny probes that look like scale models. But while these approaches to asteroid exploration are very different, they are far from mutually exclusive.