Got a really, really nice explosion system working now. Can't really get any kind of effect from a static screenshot, but this additive blending is the ticket.
Also got a basic system working so that as well as placing an explosion particle effect anywhere on the map, I can also place an explosive force point, with a radius and a strength, that correctly influences any moving entities within range.
Haven't got a projectile system quite sorted in my mind yet, so it will be a little while yet before the ship can fire projectiles, but all of the above is all going to fall into place when I do. I sort of bodged a temporary firing system together earlier just to test the theory and it looks and feels exactly like I want.
Just hope I can actually build all of this stuff into some kind of playable game.