I have been playing Angry Birds Space for a few days so far (90 out of 90 stars for Pig Bang), and so far to get three stars, you need to finish all of the levels with only one bird. I was wondering if this is true for the rest of the game. Thanks!
No, this is not true for all levels. Using less birds is only more efficient if the amount of damage done by each additional bird will net you less than 10 000 points, the amount of score you get for each bird not used.
For instance, Pig Bang 1-14 can be completed with only one bird, but to get three stars you would need to use all three to cause the maximum amount of damage, as per my answer here: http://gaming.stackexchange.com/a/57853/3936