Balloon Array for RBSP Relativistic Electron Losses (BARREL) is a NASA mission operated out of Dartmouth that works with the Radiation Belt Storm Probes (RBSP) mission.
BARREL will help study the Van Allen Radiation Belts and why they wax and wane over time. Each BARREL balloon will carry instruments to measure particles that are ejected from the Belts that make it all the way to Earth's atmosphere. By comparing such data to that of RBSP—which will be up beyond the atmosphere observing the Belts from a closer viewpoint—the two experiments can try to correlate observations in the Radiation Belts with the number of particles ejected. This will help distinguish between various theories of what causes electron loss in the Belts.(text ©Wikipedia)