The Imaging Neutral Camera for the Cassini Mission to Saturn and Titan
Krimigis, S. M.; Mitchell, D. G.; Roelof, E. C.; Mauk, B. H.; Schlemm, C. E.; Cheng, A. F.; Keath, E. P.; McEntire, R. W.; Williams, D. J.; Tossman, B. E.; Jaskulek, S. E.
Abstract
The INCA sensor is the first Energetic Neutral Atom (ENA) imager funded for flight by NASA. It is a part of 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. The investigative requirement is to perform remote sensing of the magnetospheric energetic (E≥20 keV) plasma ions by detecting and imaging charge exchange neutrals, created when magnetospheric ions capture electrons from ambient neutral gas. In fact, this instrument will work to somewhat lower energies. Escaping charge exchange neutrals, detected by the Voyager-1 spacecraft outside Saturn's magnetosphere, 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 2-D 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 on the back-plane microchannel plate, thereby establishing the ENA's trajectory and time-of-flight (TOF). 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 ∼20 keV to several MeV. A large geometric factor (∼2.5 cm2-sr) allows sufficient sensitivity to obtain statistically significant images in ∼1 to 30 minutes, for most conditions and locations. We will discuss several of the design details unique to this instrument, and will also review some of the its limitations as well as modifications required for imaging in the Earth magnetospheric environment.