We had a space theme for our carnival a few years ago-let's see how much I can remember!
We had a kind of fishing game-called it Catch a Falling Star: dowel w/string attached and a magnet on end, star shapes w/ magnet attached to back side. We made the stars out of poster board and covered them with glitter. Made most silver and a couple gold because we had two different sizes of prizes. We made a large "wall" out of a big card board box and painted it to look like the night sky, then cut a hole in the middle where the kids would drop the fishing line through into a bucket below. Then they reeled in their catch and were given a prize according to the color.
Alien Bowling-paint 2 liter pop bottles to look like the green big-eyed aliens and set up a bowling game.
Just thought up this one: Traveling the Solar System. Set up cans of varying sizes in the layout of the solar system(biggest can-Mercury closest to the sun down to the smallest can-Pluto) and have kids toss a small ball(golf or ping-pong)into the cans. Give more points for the further tosses.
We are planning a space themed event this spring to celebrate the addition of a Space Net to our playground. Would love to hear ideas for carnival type games, decorations, and other fun things you can think of within this theme.