Begin the game with this command line parameter to enable cheats: +set ui_console 1 +set cheats 1. Then press ~ once you begin the game. At the console window, type one of the phrases below to activate the cheat.
NOTE: This involves changing a game file, so make a back-up prior to execution.
Clear the game and a new choice is available on the main menu. Unlock more by collecting the small gold communicator pins in the game.
If you'd like to simply hack the secrets, search and locate the file called *.cfg in the directory driveletter:\...\Elite Force 2\base\ and then open it with a text editor.
Now search for the line seta g_secretCount and replace it with the string seta g_secretCount "70" and save the file with a .cfg extension.