Cheat mode:
On the Title Screen when "Press Start" is flashing. Hold Select and press the following buttons in order. You will hear a sfx prompt, when the cheat is activated.

Level Select:
Square, Triangle, Circle, Triangle, Triangle, Square, Circle Once in the game, you can change levels and zones and turn collision off by:

1. During game play, press Select and Start simultaneously
2. Select level, zone, and collision state using the directional pad
3. Press L1

Unlock Fourth Ship:
Triangle, Circle, Circle, Triangle, Square, Circle, Square

Unlock Forth Ship...the hard way:
Beat the game at expert or hardcore.

Unlock Classic Asteroids Game:
Circle, Circle, Circle, Triangle, Square, Square, Circle

Unlock Classic Asteroids...the hard way:
To get the original game you must go all the way through the first mission until you get to level 15. Once you get to level 15, continue to play but look for a greenish wire-frame asteroid to come into the screen. Shoot the green asteroid and big words in green will appear on the screen letting you know the game is unlocked, but don't stop just yet. Finish level 15 and save your game so you can save the original version for fun

Armageddon:
To get armageddon without getting the power up simply hold the fire button for 5 seconds then release. This can be done in 2 player mode too.

Classic Asteroids Game Codes:

+1 Life
Up, Down, Left, Right, Circle, Square, X, Triangle

99 Lives:
Up, X, Down, Triangle, Left, Square, Right, Circle

Invincibility:
Down, Down, Up, Up, Circle, Square, Triangle, Triangle