An air balloon, left, and water balloon, right, subjected to hypergravity conditions inside ESA's Large Diameter Centrifuge. Because the water is far denser than air, the water balloon reacts to changes in gravity more dramatically. Based at ESTEC in the Netherlands, the 8-m diameter four-arm centrifuge gives researchers access to a range of hypergravity environments up to 20 times Earth’s gravity for weeks or months at a time. The centrifuge rotates at up to 67 revs per minute, with its six gondolas placed at different points along its arms weighing in at 130 kg, and each capable of accommodating 80 kg of payload.