 Thermal control was planned to be achieved by a large number of small "propeller blade" devices on the surface of the sphere.The blades themselves were made of reflective material and consist of four vanes that were flush against the surface, covering a black heat-absorbing pattern painted on the sphere.A thermally sensitive coil was attached to the blades in such a way that low temperatures within the satellite would cause the coil to contract and rotate the blades and expose the heat-absorbing surface, and high temperatures would cause the blades to cover the black patterns.