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

In the Player History screen:

Left-Shift Backspace	Add selected mission to history
Left-Shift		Toggle outcome of selected mission
Left-Shift 0		Access all missions

During gameplay:

Left-Shift P		PCX image file to PSGRESOURCEARTSCREENS
Left-Shift M		Continuous stream of PCXs (will fill up your hard disk!)
Left-Shift 8		Jump to vicinity of target
Left-Shift 9		Match velocity with target
Left-Shift 0		Explode targeted ship
Left-Shift I		Player invulnerable
Left-Shift W		Force mission win 

Thanks to Revolution readers Vyas and Arjun!