Yes it has been done before and if it had failed, no-one was going to get killed because of its failure. IN this scenario, it's different. Landing something on the surface of an asteroid is far riskier than just needing to approach it.
The most powerful Thermonuclear weapons are Fusion based in their main operation, just like the Sun. Nobody would waste a payload on a mere fission-only bomb.
Obviously the comparison was missed on you completely. So I'll explain it. The Sun is a hot dot in the sky, and the reason you get hot from that hot dot is by Radiated heat. And in my scenario, it is how most of the energy will be transferred.