Set off a baking soda and vinegar rocket, use molecular models to understand the chemical reaction that makes them fly, then model the chemical reaction in real rockets. Model gravity assist, which allows us to send spacecraft to the outer reaches of the solar system.
Science content (2016 curriculum):
Earth/Space: Sun, Moon, Solar System, Universe (1, 4, 6)
Earth/Space: Extreme Environments, Space Exploration (6)
Curriculum connection (2005 science topic):
Earth and Space Science: Stars and Planets (grade 3)