I've been trying to remember a DOS game i played when i was a kid, i'm pretty sure it was a Top Down game in space where you controlled a circular spaceship that had to survive enemies coming from 4 entrances that where at the sides of the screen.
I also remember some enemies dropping bombs (Maybe it was your spaceship that could drop bombs) and i also think that at the end of the level you had to go through the top entrance, if you crashed in the entrance border you failed the mission.
I did this quick mockup of what i remember the game to look like:
Thank You