Defender is the old version of DEEP Space. The name was changed for a few reasons. Mainly because defender.exe is the name of a virus.
I've left Defender up on the net though, but wouldn't reccomend playing it.
Deep space is the new version, and is now some-what playable. The current data package includes two levels:
Level1 - is testing ground for some enemies, with a small selection to battle.
Training - is going to be a pilot training level. There are no enemies, and there is no point to the level at this stage.