With FoundationTechnologies you can define "yield" actions for a projectile weapon impact (when the yield of the projectile is released).
Not sure what you mean with 2 extensions rotating around a centre piece, you mean 2 torpedoes at the same location? That might be tricky to do.
But FoundationTechnologies also supports "on Fire" actions, so you do an action when the torpedo is fired.
All projectiles can be made "harmless" by setting the lifetime to 0 on impact.
Further more, it's also possible to queue an action, but I'm unsure waht you mean with a second explosion (or rather, what the effect of it would have to be).