In June 1985, a laser beam was sent out from the Air Force Optical Station on Maui, Hawaii, and reflected back from the shuttle Discovery as it sped by, 394 km overhead. The diameter of the central maximum of the beam at the shuttle position was said to be 9.6 m, and the beam wavelength was 520 nm. What is the effective diameter of the laser aperture in meters at the ground station? (Hint: A laser beam spreads only because of diffraction; assume a circular exit aperture.)