Cube made of a gold-platinum alloy, known as a test mass, used in the LISA (Laser Interferometer Space Antenna) Pathfinder Space probe. It is approximately the size of a Rubiks cube. The LISA Pathfinder probe launched on 3 December 2015 to test equipment that will be used in the LISA mission to explore the nature of gravitational waves in space. The test mass is designed to float freely in a spacecraft, so that it is under the influence of gravity alone. The LISA mission, planned for a launch in the 2030s, will consist of three spacecraft, each with two of these test masses suspended in free fall. Any changes in the distance between the test masses, which lasers will measure, should in theory be a result of gravitational waves alone.