Outer Radiation Belt Injection, Transport, Acceleration and Loss Satellite
The Earth's outer radiation belt and ring current environment is extremely dynamic with 1 keV - 30 MeV energetic particle fluxes changing by orders of magnitude on timescales of tens of seconds to days and years. The figure shows the long-timescale variation of the 2 - 6 MeV electron flux precipitating into the drift loss cone as observed by the low altitude SAMPEX spacecraft. Apparent are dynamic quasi-periodic particle injections, and the inward and outward expansion of intensifications of the outer radiation belt from L~3 to beyond geosynchronous orbit. Also apparent are the slot region, separating the inner and outer belts, and the aperiodic energization and creation of new inner belt fluxes.
Few regions of the magnetosphere are as poorly understood as the inner magnetosphere. This is despite the implication of radiation belt particle fluxes in generating operational anomalies and even catastrophic failures of Earth orbiting satellites as well as generating harsh radiation doses for the crews of the international space station and for people on high latitude polar aircraft flights.
Indeed, the fundamental mechanisms responsible for the energization and loss of these particles remains largely unknown [see e.g., the review by Friedel et al., 2002]. It is clear that detailed measurements from a satellite with a full complement of instruments are required at the same time as high resolution in-situ solar wind monitoring in order for scientific progress to be made. No previous missions have offered this capability. This will be redressed by the ORBITALS. The goal of the ORBITALS mission is to "understand the acceleration, global distribution, and variability of energetic electrons and ions in the inner magnetosphere." This goal also forms the top priority objective for the NASA Living with a Star (LWS) program (see report of the LWS Geospace Mission Definition Team, September 2002).
Essential to reaching science closure for this goal is the availability of multiple satellite measurements which provide the global spatial coverage and which resolve the spatio-temporal characteristics of both the energetic particle populations, and the electric and magnetic field disturbances responsible for their acceleration and loss in the inner magnetosphere.
