Update for the Balloon Array for Radiation-belt Relativistic Electron Losses (BARREL) Mission

BARREL is a multiple-balloon investigation that will study electron losses from Earth's Radiation Belts. Atmospheric losses of relativistic electrons play an important role in radiation belt dynamics; precipitation into the atmosphere may even completely deplete the radiation belts during the main phase of some geomagnetic storms. BARREL will consist of Antarctic balloon campaigns conducted in the Austral summers of 2012-2013 and 2013-2014, during the RBSP mission. During each campaign, a total of 20 small (~20 kg) balloon payloads will be launched to an altitude of 30-35 km to maintain an array of payloads for 40 days. The balloon array will cover up to 8 hours of magnetic local time at any given moment. Each balloon will carry a NaI scintillator to measure the bremsstrahlung X-rays produced by precipitating relativistic electrons as they collide with neutrals in Earth’s atmosphere. We present a brief description of the three BARREL test campaigns and the results from each campaign. First, in December 2008, a BARREL prototype instrument was launched from McMurdo, Antarctica and carried for 54 days at an altitude of 34 km on NASA's superpressure balloon. Observations of relativistic electron precipitation were made during a small geomagnetic storm on Feb. 14-18, 2009. Second, in December 2009, four BARREL prototype payloads were hand-launched from McMurdo, Antarctica. Third, the preliminary results from the upcoming November-December 2010 test campaign will be presented. BARREL is the first Geospace Mission of Opportunity under NASA’s Living With a Star program. BARREL will support NASA's Radiation Belt Storm Probes (RBSP) mission, which is set to launch in May 2012. Antarctic operations for the 2008, 2009, and 2010 balloon campaigns were supported by the National Science Foundation.