This seems to be an idea from science fiction, and for no apparent useful purpose, but this article from the i on 2 June suggests otherwise:
Asteroids were once viewed as the vermin of the sky, disrupting astronomical observations by leaving streaks on long-exposure photographic plates used to stay the stars. How times have changed. These remnants of the early solar system are now seen as key targets for space science and possibly for space commerce. The Japanese Hayabasa space craft returned grains of dust from asteroid Itokawa in 2010. and NASA has drawn up plans for an Asteroid Redirect Mission to bring back an entire boulder from a near-arts asteroid and park it in orbit about the moon. Recent NASA funding changes mean that the project’s future looks uncertain, but there are still good reasons to capture an asteroid.
So, how could it e done? First, NAASA would launch a large robotics spacecraft using a chemical rocket and a highly efficient solar electric propulsion system to travel to a suitable asteroid. The spacecraft would then snatch a large multi-tonne asteroid boulder using a robotic grapple, before hauling the4 boulder back to the Moon. Once parked in orbit about the Moon, the boulder would provide an easy accessible target for a future crewed mission to explore sometime in the 2020s.
The asteroid mission would also provide an opportunity to test a way of nudging asteroids out of their current orbit. this “gravity tractor mechanism” could be useful if an asteroid is on collision course with Earth. Once the spacecraft had captured the boulder, it would orbit the asteroid and fire its solar electric propulsion system. As the boulder moved with the spacecraft, it would also very gently pull the asteroid along due to the weak gravitational attraction between e4h two.
Aside from creating opportunities for some fascinating space science, capturing and delivering a large boulder to the moon would open new ways of using asteroid resources. A key element of human spaceflight whether deep space or space tourism, is the provision of water. But even if future launch costs fall as low as say $1,000 (£695) per kg- current cost vary but are around $10,000 per kg- bulk water delivered to low-Earth orbit would still be at least 20 times more expensive per litre the good single malt whisky.
Water is available in he form of ice on the Moon, but it would take so much energy to lift it from the surface into orbit that it could be easier to extract it from the asteroids. Our studies have shown that a useful quantity of water is available in the family of near-earth asteroids. We could extract the water from the target rocks by bagging them in plastic and using solar heat to bake out the water resource.
This water could supply national space agencies, future space tourists, and satellite operators who could ‘crac’ the water using solar-generated electricity to get at the hydrogen and oxygen it’s composed of to use as fuel.
There is a nagging question of risk. Why push part of a near-Earth asteroid into an Earth-return trajectory? Reassuringly, the boulder would be in a stable orbit around the Moon and burn up in the Earth’s atmosphere if there was a mishap.
This all sounds brilliant, but where will the money, and more importantly, the resources come from?