A log–log plot of the average transmit power ﹩{P}_{A}^{T}﹩ for λ = 400 nm vs. the average dark counts ﹩{{\rm{\Lambda }}}_{D}^{S}﹩ per year (when referenced to individual aperture optical detectors). Sharing optical detectors across multiple apertures may be helpful in reducing ﹩{{\rm{\Lambda }}}_{D}^{S}﹩ (see Section 6.4). Idealized performance is assumed for other physical characteristics like quantum efficiency, pointing accuracy, and atmospheric refraction and turbulence. The different curves illustrate the benefit of reducing the coverage angle. The highest dark count rate ΛD = 104 yr−1 corresponds to 1.14 hr−1.