Given we already have nuclear weapons the probable risk of developing such measures is logically meaningless. It's not like we are giving nasa armed ICBMs ready

Given we already have nuclear weapons the probable risk of developing such measures is logically meaningless. It's not like we are giving nasa armed ICBMs ready to fire at a moments notice. We are merely exploring a new use for existing hardware which could be deployed in a reasonable time frame. We also aren't liable to experiment on any mountain sized rocks and accidentally steer it into our path. We can absolutely experiment with manageable sized rocks. The only meaningful risk other than wasting our money is dealing with something that is within the margin of error and turning a near miss into a hit. As this risk is inherently a small subset of the probable hits its hard to imagine how this risk could possibly be larger than its superset. The remaining risk would be in an accident during a test run involving a live nuke. It's not obvious that such a test would be advantageous to conduct on balance nor needed.