At the main menu, hold both triggers and press Left, Up, Down, A, Right, B, Start. This will bring up the code entry screen. Now enter the following cheats.
SUPERMECH Invincibility WHERESMAX All models are awards WEWILLWIN Level select MULTIMAYHEM All multiplayer levels SPACEFOLD Gunpod refresh faster MARSBASE Missiles refresh faster MIRIYA Gunpod and missiles refresh faster BACKSTABBER One shot kills SNIPER One shot sniper kills MISSMACROSS All paint schemes FLIPSIDE Upside down mode CLEAR Turn off codes
Go into Training mode, pick the Veritech Fighter training, shoot down only the first two targets, then quit the game. Now go into Story mode and you'll be indestructible no matter the stage or style of fighter that you choose.
Thanks to Revolution readers -TroJax-, Aaron Ortega, and Ginger!