Radiometric Modeling for Breakthrough Starshot: How Sail Shape and BRDF Impact the Adaptive Optics

Abstract

The Breakthrough Starshot program is an ambitious project to achieve interstellar travel by using a massive laser array to propel a nanocraft to 20% the speed of light over 10 minutes and send it to the next closest star within 20 years. For the laser to make it through the turbulent atmosphere and efficiently transfer its momentum to the solar sail on the nanocraft, an Adaptive Optics (AO) system is needed to correct the aberrations introduced to the laser by the atmosphere. However, these aberrations can’t be corrected unless there is a beacon on the other side of the atmosphere to measure the turbulence. This thesis proposes that the ideal beacon, after the first 30 seconds, for the AO system is the nanocraft itself. For this purpose, a radiometric Matlab model has been developed to simulate the return photon flux of the light that hits the nanocraft and returns to Earth. This will also model how the sail shape and BRDF caused by the sail material will contribute to the return flux and in turn, the performance of the AO system.