Key stage 12: consider Nasa's plans to set up a Moon-base permanently.
Design a housing unit that space travellers could live in. What would be needed considering the gravity? Would it be designed like a house on Earth? Make a model in card.
KS3: make a model to show the scale of Earth and Moon and Earth and Mars.
Place a line between Earth and Mars with a scaled spaceship. The spaceship can be moved the correct distance each day.
KS4+: consider the characteristics of Mars' atmosphere. Why would we want to live on Mars? What are the advantages and disadvantages. The US and Europe have both sent robots to the surface of Mars; they have had mixed fortunes. Meanwhile a third from the US has landed. Would it be better and cheaper for the human race to work together sending out joint expeditions to space?