Apparently, manufacturing metals in space could boost the efficiency of hydrogen engines and aircraft. The European Space Agency is planning to head up to the International Space Station where they'll begin manufacturing lightweight metal compounds in zero-gravity.

ESA scientists are currently testing intermetallic materials, combinations of metal similar to alloys in which two or more metals are diffused together on a molecular level. Titanium aluminide is an intermetal that could cut the weight of fan blades in jet engines by half. Unfortunately, titanium aluminide tends to fail under high temperatures. This can be solved by introducing small amounts of other materials, such as niobium. In Earth gravity, weight differences between the different metals makes it difficult to get them to diffuse properly.

BBC, via io9