The Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) on the two Van Allen Probes spacecraft is the magnetosphere ring current instrument that will provide data for answering the three over-arching questions for the Van Allen Probes Program: RBSPICE will determine "how space weather creates the storm-time ring current around Earth, how that ring current supplies and supports the creation of the radiation belt populations," and how the ring current is involved in radiation belt losses. RBSPICE is a time-of-flight versus total energy instrument that measures ions over the energy range from ∼20 keV to ∼1 MeV. RBSPICE will also measure electrons over the energy range ∼25 keV to ∼1 MeV in order to provide instrument background information in the radiation belts. A description of the instrument and its data products are provided in this chapter.

Measurements from the Cassini Magnetospheric Imaging Instrument (MIMI) beginning in July 2004 reveal that sudden planetward injections of energetic ions (5–200 keV) and electrons (20–200 keV) over confined regions of azimuth are pervasive events in Saturn's magnetosphere over the radial range of 3.8 to 11.2 Saturn radii (RS). Saturn is thus similar to both Earth and Jupiter in the pervasiveness of such injections. At Saturn with Cassini, unlike Jupiter with Galileo, effects of the large radial gradients in the global azimuthal rotational flow pattern often dominates the dispersive particle injection signatures. Accurate knowledge of rotational flow patterns is required to calculate the age and formation positions of injections that are more than several hours old. Here we develop procedures to derive the needed flow profiles from the injections themselves.

The Magnetospheric Imaging Instrument (MIMI) onboard the Cassini spacecraft observed the saturnian magnetosphere from January 2004 until Saturn orbit insertion (SOI) on 1 July 2004. The MIMI sensors observed frequent energetic particle activity in interplanetary space for several months before SOI. When the imaging sensor was switched to its energetic neutral atom (ENA) operating mode on 20 February 2004, at approximately 10(3) times Saturn's radius RS (0.43 astronomical units), a weak but persistent signal was observed from the magnetosphere. About 10 days before SOI, the magnetosphere exhibited a day-night asymmetry that varied with an approximately 11-hour periodicity. Once Cassini entered the magnetosphere, in situ measurements showed high concentrations of H+, H2+, O+, OH+, and H2O+ and low concentrations of N+. The radial dependence of ion intensity profiles implies neutral gas densities sufficient to produce high loss rates of trapped ions from the middle and inner magnetosphere. ENA imaging has revealed a radiation belt that resides inward of the D ring and is probably the result of double charge exchange between the main radiation belt and the upper layers of Saturn's exosphere.