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RoninTenkai: I assure you that destroying the asteroids will help you get a lot farther. During testing I got up to wave 94. But yes, sending asteroids out to space is somewhat based on luck but is mainly for the gravity blast. You can, however, get in front of the asteroids and accelerate them off the screen (very dangerous). Thanks for the feedback.
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I usually find myself not killing many of the asteroids but trying to dodge them as far as possible before the first hit to get the population bonus. Also sometimes I don't know when I get the asteroids sent to space and at times I was able to avoid the asteroids even though it look like it hit me. Its a pretty decent game.