Unlimited weapons, energy, and shields:
Hold Down + 3 + 4 + 6 + 7 at the mission selection screen. You will hear a sound if you have entered the code correctly.

Bonus lives:
Hold 3 + 6 + 9 + # at the mission selection screen. You will hear a sound if you have entered the code correctly. Up to nine extra lives may be selected.

Level skip:
Hold 2 + 4 + 6 + 7 + 8 + 9 at the mission selection screen. You will hear a sound if you have entered the code correctly.

Switch day and night:
Hold Up + A + B + C + 7 while playing the game.

Alter globe speed and direction:
Hold 4 + 6 at the mission selection screen.

Display alternate monitor frame:
Press Right + C + 1 + 4 + 5 at the mission selection screen.

Alternate ground appearance:
Hold Up + A + B + C + 3 while playing the game.

Debug mode:
Press Up + A + B + C + 6 while playing the game. The top right number indicates the current frame rate.

Music select:
Press Up + A + B + C + 0 while playing the game.

Alternate "Ammo depleted" notice:
Press C + 4 + 8 at the mission selection screen.