Metamaterial-Enhanced Graphene as a Beamed Energy Sail for Interstellar Probes
Author: Joseph Meany, Ph.D., Principal, Ionic Flask Materials Group
The primary goal of solar sail research is to identify materials whereby the structure has as low a mass as possible while maximizing its reflectivity. Selecting pure substances for their intrinsic bulk reflectivity is limiting. Bulk masses are defined by the atomic or formula mass of the material used. To date, effort has focused on developing multilayer thin-film approaches in order to increase the reflectivity. The best modern reflectors involving uninterrupted thin film substrates unfortunately suffer from high areal density due to their thickness. It is absolutely key to reduce this mass in order to produce a sail capable of high acceleration and high speed.
While metal films on a polymer substrate are the current state-of-the-art in solar sail design, excitement has grown over the last decade on using graphene as a replacement substrate both for its durability and its low areal density. Graphene by itself, however, is almost entirely transparent. Therefore it is necessary to deposit some inherently reflective material onto the Earth-ward surface of the graphene monolayer. Optical metamaterials have recently achieved near-perfect reflectivity in the NIR region of the electromagnetic spectrum using nano-patterned Si cubes. Here, the determination of basic parameters concerning the metamaterial-on-graphene solar sail is presented, alongside some promising areas of further research.