At the player history screen type DARKGOAT to enable cheat mode.

In the Player History screen:

Left-Shift BackspaceAdd selected mission to history
Left-ShiftToggle outcome of selected mission
Left-Shift 0Access all missions

During gameplay:

Left-Shift PPCX image file to PSGRESOURCEARTSCREENS
Left-Shift MContinuous stream of PCXs (will fill up your hard disk!)
Left-Shift 8Jump to vicinity of target
Left-Shift 9Match velocity with target
Left-Shift 0Explode targeted ship
Left-Shift IPlayer invulnerable
Left-Shift WForce mission win 

Thanks to Revolution readers Vyas and Arjun!