Sounds like a realistic situation. Earth has never had a very good interstellar defense. :) I like the spacy techno music in the game, reminds me of some space venture I've seen somewhere. Also nice how the game pauses automatically as soon as you focus on an area outside the flash, that's useful.
The two control options, pro and simple, is a nice selection, and the concept of catching enemy ammunition with your shield is pretty neat. The gameplay itself is smooth and simple, and I like the sprite style used, it's a lot of fun. Keep it going!
-cd-