Can someone please help me find this Movie?

[kashubhaj]

Hello, I watched a movie when I was younger and would like to re-watch it, however, I have no idea what it was called I could only remember a few images.

I remember they were in space and meant to drop a bomb on a foreign planet, but something happened and they dropped it on earth by mistake.

Another scene from the film was a fight and someone lost the top of his head and you could see his brain.

Sorry for the lack of info.