Fig. 1: Mission parameters for lightsail mission to Alpha Centauri.

d, distance; t, travel time; A, ligthsail area; v, velocity; m, mass; I, power density; λ, laser wavelength. High power earth-based laser propelling a fleet of lightweight sails to 20% of the speed of light, to reach Alpha Centauri in 20 years2. The lightsail needs to be reflective over a broad bandwidth due to the Doppler red-shift of the laser resulting from the change in velocity of the sail. The minimum feature size (MFS) of a photonic crystal based lightsail is related to the fabrication cost. A commonly used performance metric for a lightsail is the acceleration distance. The launch cost is mainly determined by the energy consumption of the laser43.