BARREL is the acronym for Balloon Array for RBSP Relativistic Electron Losses a multiple-balloon research program designed to study electron losses from Earth's Radiation Belts. The inititative is a NASA mission operated out of Dartmouth College that works in coordination with the Van Allen Probes mission (formerly known as the Radiation Belt Storm Probes mission).
In the scheme at left we can see three different views of the elements that compose a BARREL payload: (a) the internal payload structure, (b) a mechanical cutaway drawing and (c) the fully assembled payload including foam enclosure and solar panels (click to enlarge).
Each BARREL payload contains a single 3 inches high by 3 inches diameter NaI scintillator which provides a good compromise between energy resolution, detector efficiency and cost. The scintillator crystal is coupled to a photomultiplier tube (PMT) and signal processing electronics. The scintillator crystal, the PMT, a high voltage converter and a preamplifier, are all housed in a light-tight aluminum tube. The assembly is wrapped with a layer of mu-metal shielding to prevent Earth's magnetic field from modulating the PMT gain as the balloon payload rotates or swings. Mounted on a 42" long boom protruding from the external part of the gondola is a three-axis magnetometer which is used to identify magnetic activity, since ground-based magnetometers are often not available near the balloon locations in remotes areas. Time and positioning are provided by a GPS module.
An onboard computer called Data Process Unit (DPU) acquires data from the X-ray spectrometer, magnetometer, GPS, and an engineering data interface. It outputs formatted data frames to an Iridium modem for downlink, and also controls the command-cutdown system.
The gondola design consists of an internal frame constructed of aluminum angle, a foam enclosure, and an external aluminum frame for attaching the flight train and solar panels and to assure an easy launch. Handles made of square rails allow for easy transport and launch.
The BARREL power system is based on a solar-charged nickel metal hydride (NiMH) battery that powers a box of DC/DC converters which provide isolated regulated voltages to payload components. As the payloads are freely spinning under the balloon the power system relies on 4 identical solar panels, one for each side of the gondola.
Balloon launched on: 12/31/2013 at 11:44 utc
Launch site: Halley Research Station, Antarctica
Balloon launched by: Dartmouth
Balloon manufacturer/size/composition: Zero Pressure Balloon
End of flight (L for landing time, W for last contact, otherwise termination time): 1/15/2014 at 21.28 utc
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): ~ 14 d
Landing site: At latitude 74.54 S, longitude: 51.37 E, Antarctica
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