Make a Nanorover

"Make a balloon-powered Nanorover!  NASA built a tiny rover just a couple of inches high to explore the surface of an asteroid and take pictures."

"You can build a nanorover too. Try this one, made from three styrofoam meat trays."
  
"This project is a little bit hard, so you might want to ask a grown-up or big brother or sister to do it with you."