A new preprint of relevance:
A quote from the preprint:
Proposals using large light sails like the Starshot Breakthrough, require mirrors with lateral sizes of 4 × 4 m2, thicknesses of 0.05 lambda, reflectivities of 90 %, ppm level optical absorption and a total mass of only 1 g .
Our PhC are designed with a lattice of holes which remove about 30 % of the mass of the membrane. Additionally, they are made of LPCVD SiN which has an imaginary refractive index of about 1.0E-6 at 1064 nm and has been shown to withstand high laser powers of around 2.5E+11 W/m2 – nearly 2 orders of magnitude more than what is required for the initiative.
Thus the needed material is at hand. Initially sprite-sats to other star systems may suffice, but eventually we’ll want to send bigger vehicles. A much higher power level means higher acceleration and so a Sail-Beam can be contemplated for pushing a bigger vehicle via a stream of sails. A Beamer for pushing the micro-sails at one frequency, and a Blaster to ionise the sails at another frequency, should be straightforward to engineer. Albeit at a GW power-scale.
Where to site the Beamer? One possibility is the far side of the Moon, so it can never be pointed directly at the Earth. Stephen Baxter made this suggestion in a novella anthologised in “Starship Century” in 2013. His fictional star-probe’s Beamer was powered by a huger solar-array refined straight out of lunar regolith. To that end we can practice deploying the technology in Earth’s deserts – simultaneously creating a vast generating capacity. Such a remote array, when not pushing Star-chips, could power CO2-absorbing “Fuel Factories” that turn the 20th Century’s waste gases into usable fuel, shippable to anywhere in the world via solar-powered airships. Or via more conventional compressed gas-lines if available.