Bringing an asteroid into LEO may be too dangerous due to orbit decay. According to this calculator, a 500ton roughly spherical rock, assuming a density of 3g/

Bringing an asteroid into LEO may be too dangerous due to orbit decay. According to this calculator, a 500ton roughly spherical rock, assuming a density of 3g/m^3 so a surface area of 3600m^2 would live for 20 years at 500km altitude. http://www.lizard-tail.com/isana/lab/orbital_decay/ http://www.lizard-tail.com/isana/lab/orbital_decay/ At altitudes higher than 1000km, the thing could live for centuries, although no matter how high, orbits still get perturbed eventually and decay (in the Earth-Moon system). (Note that at 380km altitude, the ISS is never more than 1-2 years away from burning up in the atmosphere, so it needs periodic boosts to prevent it)