Unlock Ellen McNichol
During yourgame campaign, shoot down Ken with Albert everytime Ken is on the map. Eventually, two cutscenes will play concerning Ellen, and she will be playable for the space missions.

Vic-Viper And MX5000
Complete the game, and save your game file, now start a new game with your saved game file and on the hanger screen press SQUARE. You will enter a second hanger containing the Vic Viper and MX5000.

Vic-Viper Self Destruct
While flying the Vic Viper, pause the game, and press Up, Up, Down, Down, Left, Right, Left, Right, X, Circle.

Character Viewer
Beat the game once.