Although everyone thinks of space as very cold, in fact, if you stood on the sunny side of the moon, the temperature would be hot enough to boil the blood in your body. Spacesuits are designed to protect astronauts from these extremes of temperature. So for this week's challenge the Rough Scientists have to collectively design a cooling system for their very own spacesuit. And to test it out, at the end of day three, they're going to have to go to Death Valley and do a mock moon walk in their spacesuit - hopefully staying deliciously cool.

They decide that they need to make a portable Rough Science fridge. Ellen creates a copper pipe system that will go from the fridge to the spacesuit, carrying cool water from the fridge to the astronaut. Jonathan devises a pump to keep the water moving through the system.

Kathy suggests that the fridge should use the principle of evaporation - the same principle that cools us when we sweat. She needs to get water evaporating inside the fridge. And the best way to do that is to lower the pressure; this speeds up evaporation and therefore cooling. But there's a problem - all that evaporating water is trapped inside the fridge, and unless they can get it out then it will destroy the vacuum. Fortunately there's a magic mineral called zeolite that has a special property - it absorbs water vapour. So if they can find zeolite and put it in the fridge it will suck up the water vapour, preserving the vacuum. Mike attempts to extract zeolite from washing powder, whilst Iain tries to find naturally occurring zeolite in the rocks around the mine.

So at the end of day three the Rough Scientists decamp to Death Valley where Ellen is dressed in their spacesuit for a spacewalk which will reveal whether their cooling system really can keep someone cool in one of the hottest places on Earth.