To enter these cheats go to options and select password to input.
267776 8 Credits
220969 start with 9 ships
713948 start level 2
900277 start level 3
213490 start level 4
866141 start level 5
321904 start level 6
196861 start level 7
040186 start level 8
841003 start level 9
216409 start criticus
180771 invulnerable ship
300167 end sequence