Load the game as usual and don't do anything until the high 
score screen appears.  Type 'COMMANDER' and then press the 
fire button.  After a few moments press F10.  If your ship 
flickers you are now invulnerable, and have infinite expansions 
and smart bombs. 
 
F1-F5 = Other Six Levels of 'expansion' (you can still capture 
      = the capsules) 
F8    = Advance a level (There are three) 
F10   = Turn cheat mode on/off 
 
You cannot get a high score with the cheat mode on.