No space mission can succeed without communication, so our second set of Rough Science space challenges are all based around making contact. Jonathan and Kathy have to come up with a way of communicating that doesn't use sound waves - because in the vacuum of space, there's nothing for them to move through. It took two years and a million pounds to develop a pen for use in space - one that would work in zero gravity. Ellen and Mike have no money and just three days to come up with their own version. Iain's challenge is very different. He has to find a way to communicate with aliens!

• Kate Humble
• Iain Stewart