 Dyson estimated that if the exposed surface consisted of copper with a thickness of 1 mm, then the diameter and mass of the hemispherical pusher plate would have to be 20 kilometers and 5 million tonnes, respectively.100 seconds would be required to allow the copper to radiatively cool before the next explosion.It would then take on the order of 1000 years for the energy-limited heat sink Orion design to reach Alpha Centauri.