5/6. In 1872 an earthquake in California became one of the biggest ever recorded in the United States. In one of three very different challenges this week, lain and Ellen have to find where the epicentre was and work out its magnitude. Kathy and Jonathan have to design an aerial surveyor that can float over the desert. And Mike has to build a carbon dioxide filter, similar to the one created in 1970 by the crew of the Apollo 13 spacecraft after an accident damaged oxygen tanks. Presented by Kate Humble. Directors Alexis Girardet. Milla Harrison ; Series producer Jonathan Renouf