Space-themed birthday parties have been popular with children (and even some adults) for years. Serving an appropriate cake for the occasion doesn't have to be a budget-killer; there are simple ways to create an awesome birthday cake that will please even the pickiest future astronaut.
Easy Cake Ideas
Some of the easiest space-cake ideas involve baking a round layer cake as usual, then using simple decorating: For a sun, use orange frosting, then add skewers (even spaghetti will do) with different-sized marshmallows painted with food colouring staggered at different lengths to resemble the planets in our solar system. For a moon, use white frosting or whipped cream, and add rock candy, honeycomb or other appropriate cereal, and toy astronauts or a miniature flag. For a Saturn cake, you may have to use either a dome-shaped baking pan or cut one of the cake layers into a smaller size and mound up the frosting to create a half-planet with coloured frosting and fun foam surrounding it to represent Saturn's rings. For a Mars cake, use red frosting and add miniature Martian toys or space rovers/robots bought or made out of foil. For a "universe" or night-sky cake, frost the cake in dark blue or black icing, then use white icing to create stars and coloured frosting for the sun, moon and planets.
Cakes for the More Adventurous
If you are comfortable with cake baking and decorating, you can branch out a bit: For spaceships like the shuttle, start with a 9x13 cake, then using a template you create or find in a book or download from the Internet, cut the body of the ship in the middle of the cake and use the scraps to craft the tail and wings, "gluing" everything together with white fondant frosting and black detailing; for totally round planets, use a sports-ball mould you can buy at crafts and home stores, bake the two halves and then glue them together with frosting, decorating the outside with the colours of whichever planet you're recreating.
If You're Pressed for Time
Of course, if you don't have much time, you can always order a space-themed cake from a bakery. Or there are several cake toppers you can purchase from crafts and home stores, as well as online via sites like HometownCelebrations.com, Thepartyworks.com, and Birthdaydirect.com. These edible and non-edible toppers are available in Star Wars, Star Trek and other space/astronomy themes for sheet cakes and cupcakes.