Losses (BARREL)" (the other one was the Woodger et al 2015 paper). This first paper was written prior to the first mission. It was a way to ensure that the community knew this mission and it's data was forthcoming, as well as provided detailed information on the instruments.
The BARREL mission was a mission of opportunity for the Van Allen Probes... Okay, so what does that mean. NASA has large missions. I mean if you are going to send something into space, it's not every day that one gets to do that, so you often try to get the most out of each opportunity. Financially and practically, you can't fit all the instruments or have all the observations that you may like to have though on any given mission. However, for a fraction of the price of the original mission, you can have a mission of opportunity that will add to the value of the primary mission. That is where BARREL came in.
The Van Allen Probes mission was the first mission in about 20 years which was launched with the specific intent to study the Earth's radiation belts. They were designed to be two spacecraft which would fly through the radiation belts every 9 hours. This would allow them to study how the particles that are trapped in the radiation belts change during space weather events. The Van Allen Probes would attempt to see what fraction of these particles would fall and be lost in the Earth's atmosphere, but that is hard to do from their orbit. The BARREL mission was designed to study what particles from the radiation belts were lost to the atmosphere. Both missions have their own goals which will advance science on their own. But, they are synergistic and better together!
The proof is always in the pudding. Given the number of papers from the Van Allen team, and the BARREL team, I'd say that we had a successful mission of opportunity. We were able to test different theories of wave-particle interactions, see how shocks can cause particle loss, and study more about other loss processes.
So why do you care... Well the radiation belts are filled with particles which can cause harm to satellites, and when lost to the atmosphere, disruptions to communication systems and increase radiation at aviation altitudes. Being able to study one aspect - say just the loss to the atmosphere or just the stuff that stays trapped in the radiation belts - is nice, but it doesn't give you the whole picture. Even with these two missions we don't have the whole picture. We have more than what we've ever had, but there is still a lot of unanswered questions. But that's the way of science, slow and steady progress to understanding how nature works.
And of course - Here's my video about the BARREL mission that NASA helped publish! I was very proud of that.