Wait until cargo/energy screen appears, move the cursor to the top left-hand corner with the joystick, then press fire and '+' on the keypad simultaneously. The screen should flash and you will be furnished with infinite shields and lives.
To get to the end of the game, simply go to the outer-most planet.
|F1 - Disable enemies|
|F6 - Restore energy|
|0-9 - Gain different weapons|