You've probably played Scorched Earth (or a clone such as Gorillas for QBasic, Cannon Fodder for Macintosh, Scorched Tanks, or Worms). Solar Wars is yet another Scorched Earth clone, this time for the NES by Chris Covell, author of several NES demos. It's the first professional-quality NES game to have its source code released by the author. (It's unclear whether or not Solar Wars is free software.) It's a 64 KB CNROM game that puts two players (sorry, no CPU opponent) in control of tanks on various planets. The + Control Pad controls angle and power of the shot, B + Control Pad moves your tank, and A fires. Blow through the terrain in the way and hit your opponent several times to win.
Solar Wars and the rest of Chris Covell's work can be found at http://www.sfu.ca/~ccovell/ along with instructions for putting Solar Wars into a real cartridge (only if you're experienced with solder).
As usual with graphically demanding NES titles, the game probably runs like crap in NESticle. Use LoopyNES, FCE Ultra, nesterj, BioNES, RockNES, or NESten instead.