Start the game with the command-line parameter '-redrum -stendek'. Now during gameplay, press any of the following:
Mission Complete AUTO
Mission Complete MANUAL
Use a text editor to edit the "player_start.des" file in the "/aquanox/dat/sav" folder. Enter "999999" as the number of credits in that file. Always make a backup before modifying game files.
(supplied by: shoboy22)