Imaging-neutral camera (INCA) for the NASA Cassini mission to Saturn and Titan

The INCA sensor is the first energetic neutral atom (ENA) imager funded for flight by NASA. It is a part of the Magnetrospheric Imaging Instrument (MIMI) on the Cassini mission to Saturn, where it will be well suited to monitoring the global dynamics of the Saturn-Titan magnetospheric system throughout the orbital tour. INCA will perform remote sensing of the magnetospheric energetic ion plasmas by detecting and imaging charge exchange neutrals, created when magnetospheric ions capture electrons from ambient neutral gas. The escaping charge exchange neutrals were detected by the Voyager-1 spacecraft outside Saturn's magnetosphere, and can be used like photons to form images of the emitting regions, as has been done at Earth. Since Cassini is 3-axis oriented, INCA is designed as a 2D imager with a field of view of 90 by 120 degrees. The technique involves sensing the position of the ENA as it penetrates an entrance foil and again ont he back-plane microchannel plate, thereby establishing the ENA's trajectory and time- of-flight. Along with rough composition determined by pulse- height analysis, the sensor produces images of the hot plasma interaction with the cold ambient neutral gas as a function of species and energy, from approximately 20 keV to several MeV. A large geometric factor allows sufficient sensitivity to obtain statistically significant images in approximately 1 to 30 minutes, depending on conditions and location. We will discuss several of the design details unique to this instrument, as well as recent calibration results.