[hinckley buzzard]

This was not much of a secret, as I recall hearing about it in the open media at the time. Of course, "blowing up the moon" is tabloid crap. A nuclear burst on the moon visible from earth would have been something different and impressive to say the least, but it was never much more than idle brainstorming. The concern about "danger to people on earth" is patent nonsense, since at the time we were testing nuclear weapons in the atmosphere right here at home.

[HiTech RedNeck]

The danger would have come if the rocket somehow did not make it to the moon, especially if it failed in low trajectory. Presumably the bomb would be set not to go boom in such an event, but it would be a source of radioactive dirt.