Summary

The Visible Imaging System (VIS) for the Polar spacecraft is presented. Global images of the nighttime aurora at visible wavelengths are to be gained over time periods that allow continual recording of all phases of a single auroral substorm. The selected wavelengths can be used to map the electron energy influxes into the auroral and polar ionospheres, and to determine the precipitation patterns of protons from the plasma sheet and its nearEarth extension, the ring current. The scientific objectives range from provision of a reference system for simultaneous in situ observations of fields and particles with magnetospheric spacecraft to studies of the global responses of the auroras as the solar wind fluctuates. Substantial improvements in the overall capabilities of the VIS relative to previously flown imagers are gained from a combination of a high-altitude polar orbit, a despun platform for staring at the auroras, improved optics and sensors, and a generous telemetry rate that is augmented with image compression.