In early August, scientists from the NASA-funded Balloon Array for Radiation belt Relativistic Electron Losses, or BARREL, mission arrived in northern Sweden for a third data collection campaign.
Following two 20-balloon Antarctic campaigns in 2013 and 2014, this year’s mini-campaign will involve six scientific balloons. Launched over the course of several days, the balloons will gather measurements of electrons raining down to Earth from the huge swaths of charged particles magnetically trapped in two donut-shaped belts around Earth, called the Van Allen belts.
This electron rainfall, when it occurs, reveals itself by a telltale glow of X-rays. These X-rays are the by-product of electrons striking atoms and molecules in the upper atmosphere. BARREL’s balloons are equipped with a payload of sensors to observe these emissions.
The BARREL mission, led by Robyn Millan at Dartmouth College in Hanover, New Hampshire, relies on campaigns of numerous balloon launches near Earth’s poles to study electrons that escape from the radiation belts around Earth. BARREL was originally conceived as a complement to NASA’s Van Allen Probes mission, which orbits directly through the radiation belts. By comparing X-ray measurements from BARREL — taken some 20 miles above the surface — to measurements taken from within the belts, scientists can better understand what mechanisms allow the electrons to escape out of the belts allowing some to race down magnetic fields lines to Earth. Since Earth’s magnetic field lines come down to the ground near the poles, the far north and south are the best places to investigate the behavior of these lost electrons.
The BARREL team will be in Sweden for at least three weeks as they wait for favorable conditions to launch each of the six balloons. BARREL balloons are only 90 feet in diameter, much smaller than the typical football field-sized balloons used by the majority of scientific balloon projects. This smaller size means that the instruments carried by the balloons must also be smaller and lighter than those on full-size scientific balloons. These smaller balloons have the advantage of being easier to launch, allowing for multiple balloons to be launched in a short timeframe.
Each balloon can fly for up to two days, collecting data from within the stratosphere. For this campaign, the BARREL team is also coordinating data collection and analysis with several other missions that regularly orbit through Earth’s magnetic fields, including NASA’s Magnetospheric Multiscale mission, NASA’s Time History of Events and Macroscale Interactions during Substorms mission, and the joint European Space Agency and NASA Cluster mission, in addition to data collected by the Van Allen Probes team.