The Radiation Belt Storm Probe (RBSP) is actually two satellites that will travel on a elliptical orbit around the Earth, ranging between 1.5 and 6 Earth radii. This range covers the inner region of the Earth's geomagnetic field.
In this region, many of the magnetic field lines intersect the surface of the Earth in the north and south. This means that lower energy ions and electrons, some 'boiled off' the Earth's ionosphere by solar ultraviolet radiation, can be trapped along these field lines. The charged particles spend their time bouncing between the 'mirror points' in the Earth's magnetic field. This trapped population forms the radiation belts around the Earth. The radiation created by this charged particle population can be hazardous to satellites and astronauts so it is important to understand their characteristics.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 126.96.36.199.0