correction is using high speed look up tables that are pre-generated by least square fitting to polynomial functions by the on-orbit processor. The instruments were calibrated individually while on stationery platforms, mostly in vacuum chambers as described in the companion papers. Extensive ground-based testing was performed with visible and near UV simulators mounted on a rotating platform to estimate their on-orbit performance. High-Energy Neutral Atom Imager (HENA) The High-Energy Neutral Atom (HENA) imager on IMAGE is one of three instruments designed to make observations of the Earth's magnetospheric environment using neutral atom imaging. The HENA instrument determines the velocity, trajectory, energy, and mass of ENAs in the 10-500 keV energy range and from these data generates images of ENA source regions in the inner magnetosphere. The two main HENA components are the sensor and the main electronics unit (MEU). The HENA sensor consists of alternately charged deflection plates mounted in a fan configuration in front of the entrance slit, three Microchannel plate detectors (MCP), a solid-state detector (SSD), two carbon-silicon-polyimide foils (one at the entrance slit, the other placed just in front of the back MCP), and a series of wires and electrodes to steer secondary electrons ejected from the foils (or the SSD) to the MCPs. Power for the MCPs and deflection plates and for secondary electron steering is provided by high-voltage power supplies that reside with the sensor. The MEU contains HENA's data processing unit (DPU), the analog electronics (which amplifies and processes signals from the sensor and performs housekeeping monitoring), analog-to-digital converters, and a low-voltage power supply. HENA determines the velocity of the ENAs that it detects by measuring their time of flight (ToF) and trajectory through the sensor (from the entrance slit either to the back foil and two-dimensional imaging MCP detector or to the SSD. When an incoming ENA passes through the entrance foil, it produces secondary electrons, which are accelerated and steered to the front imaging MCP. This MCP, the "start" MCP, provides a start signal for the TOF analysis and registers the position at which the ENA penetrated the entrance slit. The ENA then continues through the sensor to the backplane and strikes either the foil in front of the 2-D imaging MCP or the SSD. In the first case, secondary electrons ejected from the back foil trigger a stop pulse in the 2-D imaging MCP, which also registers the position of the