  The transverse radiation pressure force and acceleration is compared for two
parametrically optimized designs: prismatic and two-pillar metasurface
gratings. The numerical results were cross-verified with both Maxwell stress
tensor and modal analysis. Solar blackbody irradiance was assumed for
wavelengths ranging from 0.33 [um] to the grating cutoff at 1.5 [um],
encompassing 83% of the solar constant. This multi-objective optimizer study
found that neither design comprised Si3N4 performed as well as those
corresponding to a low refractive index, low mass density material. The
predicted transverse acceleration of the optimized low-index metasurface
grating is compared to that of a state-of-the-art reflective solar sail.
