  We perform finite element simulations to study the impact of defect-defect
interactions on the pressure-induced buckling of thin, elastic, spherical
shells containing two dimpled imperfections. Throughout, we quantify the
critical buckling pressure of these shells using their knockdown factor. We
examine cases featuring either identical or different geometric defects and
systematically explore the parameter space, including the angular separation
between the defects, their widths and amplitudes, and the radius-to-thickness
ratio of the shell. As the angular separation between the defects is increased,
the buckling strength initially decreases, then increases before reaching a
plateau. Our primary finding is that the onset of defect-defect interactions,
as quantified by a characteristic length scale associated with the onset of the
plateau, is set by the critical buckling wavelength reported in the classic
shell-buckling literature. Beyond this threshold, within the plateau regime,
the buckling behavior of the shell is dictated by the largest defect.
