Scientists have found a way to recycle human urine into food supplements and plastics, an advance that may make long duration space trips more feasible. Astronauts can not take a lot of spare parts into space because every extra ounce adds to the cost of fuel needed to escape the Earth's gravity. "If astronauts are going to make journeys that span several years, we will need to find a way to reuse and recycle everything they bring with them. Atom economy will become really important," said Mark A Blenner, from the Clemson University in the US. The solution lies in part with the astronauts themselves, who will constantly generate waste from breathing, eating and using materials. Unlike people on Earth, Blenner said, spacefarers would not want to throw any waste molecules away. Researchers are studying how to repurpose these molecules and convert them into products the astronauts need, such as polyesters and nutrients. Some essential nutrients, such as omega-3 fatty acids, have a shelf life of just a couple of years, said Blenner. They will need to be made en route, beginning a few years after launch, or at the destination. "Having a biological system that astronauts can awaken from a dormant state to start producing what they need, when they need it, is the motivation for our project," Blenner said. The biological system includes a variety of strains of the yeast Yarrowia lipolytica. These organisms require both nitrogen and carbon to grow. Researchers discovered that the yeast can obtain their nitrogen from urea in untreated urine. Meanwhile, the yeast obtain their carbon from CO2, which could come from astronauts' exhaled breath, or from the Martian atmosphere. However, to use CO2, the yeast require a middleman to 'fix' the carbon into a form they can ingest. For this purpose, the yeast rely on photosynthetic cyanobacteria or algae provided by the researchers. One of the yeast strains produces omega-3 fatty acids, which contribute to heart, eye and brain health. Another strain has been engineered to churn out monomers and link them to make polyester polymers. Those polymers could then be used in a 3D printer to generate new plastic parts. Researchers are continuing to engineer this yeast strain to produce a variety of monomers that can be polymerised into different types of polyesters with a range of properties. For now, the engineered yeast strains can produce only small amounts of polyesters or nutrients, but the scientists are working on boosting output. They are also looking into applications here on Earth, in fish farming and human nutrition. For example, fish raised via aquaculture need to be given omega-3 fatty acid supplements, which could be produced by Blenner's yeast strains.