Imagine the accuracy of terrestrial weather forecasts if society relied on only a handful of isolated weather stations to supply all the input to meteorological models. Yet that is precisely the daunting situation faced by space weather forecasters, who seek to predict when and how ejections of plasma from the Sun will interact with the Earth's magnetosphere. These interactions can damage spacecraft electronics, produce spurious global positioning and navigation readings, interfere with radio communications, and disrupt electrical power line grids on the ground. Though modern society increasingly relies on satellite technology and electrical conveniences, only a handful of operating heliophysics missions supply the bulk of space weather model inputs.