On Earth, liquid flows downhill thanks to gravity. Creating an effective liquid fuel tank involves little more than putting a hole at the bottom of a container. That won’t work in space, though. In microgravity, with no gravity to force liquids to the bottom of a container, they cling to its surfaces instead. The Slosh Coating investigation tests using a liquid-repellant coating inside a container to control the movement of liquids in microgravity.