Hydrogen is a pretty good rocket fuel in terms of Isp, but it has a tendency to boil off in space. I still think it's very practical to consider moving asteroi

Hydrogen is a pretty good rocket fuel in terms of Isp, but it has a tendency to boil off in space. I still think it's very practical to consider moving asteroids around from a technical perspective. The political ramifications are huge. If the people in charge are malicious they could completely devastate the planet. I think this is generally solvable by using lots of small thrusters that are independently controlled to make sure that no one can smash the thing into the planet, but getting sign-off from everyone who might have veto power is huge.