We've had some time to play with Angry Birds Space, but even our hands-on didn't go into how exactly the physics of space differ from the birds' natural terrestrial environment. Rhett Allain, Wired's resident expert on angry bird movement, has now calculated the forces that act within the bubble-like region outside asteroids. After going through the first level, Allain found a constant force that acts as a sort of gravitational pull, along with a constant frictional force that pulls in the opposite direction as the bird's velocity.
The birds are launched at a similar speed as on Earth (25 m/s in space as opposed to 23 m/s), but Allain suspects they get a slight speed boost as they enter the "air" around the asteroid. You can go ahead and read the source to see his work, which includes both calculations of the birds' potential energy and scripted models that mimic the motion of a red bird in orbit.