It's not easy to defeat all pigs with the unstable steam. To get 3 stars, you should use as least birds as possible or detonate firely asteroids as much as possible.
Fire the Super Red Bird when the Mars Curiosity Rover is in the left of the right planet. Then, fire Bomb Bird to the remaining pigs from the Rover. Then shoot Orange Bird to the Moustache Pig. You should shoot the fire asteroids.