Here is the full list of all 11 Area 51 Defense achievements.
Get 2 x Kill Combo two times.
Get 5 x Killstreak five times.
Two hundred dweebs destroyed.
Two thousand enemies eliminated.
Twenty thousand enemies removed.
Two hundred thousand enemies decimated.
Two million dweebs liquified.
Survive through 10 waves without a single airstrike.
Survive through five waves without health power-ups.
Completed the game during the green hour.
Survive through the night of the dweebs.