To add some dramatic depth to your space party, you might want to consider a balloon backdrop. Unravel a long, rolled-up sheet of coil/wire, or part of a wire fence along the back of the table and anchor it with bricks. Pick up a balloon blower from a balloon store and a bunch of balloons (silver works really well), and blow them all up. Tie them into the metal. Make some smaller balloons and jam them into the little gaps in between the other balloons in the fence. Easy and inexpensive, your space age wall will really add to the whole look.