The Earth is surrounded by a donut-shaped zone of energetic charged particles called the Van Allen radiation belt. Depending on who you ask, this region is either Earth's magnetic field trapping particles from the solar wind, or a secret government project intended to protect us from aliens. NASA's sending up some armored tentacle probes to learn more.
Nobody likes radiation, least of all space probes. Most of the stuff that we send up into Earth orbit takes a lot of trouble to avoid regions of high radiation, and that new Juno probe currently on its way to Jupiter is only designed to last 33 orbits before committing suicide. In order to study the Van Allen belts, then, NASA had to come up with a design that could handle it.
The result was a pair of satellites called the Radiation Belt Storm Probes, or RBSPs.* Each probe is an octagon of 9mm thick aluminum armor, which should be enough to protect them from energetic protons and electrons and alpha particles and other things that cause electrical faults in computers and cancer in people. The armor will have a few sensor-sized gaps in it to let the sats collect data, and each one will also extend a set of cable tentacles 164 feet out into space to measure electrical fields away from the spacecraft themselves.
Assuming that the probes manage to remain alive in the Van Allen belts (the length of the mission is two years), they'll be looking for clues that should help us better predict what the weather will be like in space based on how the Earth's magnetic field interacts with the sun. This should help us figure out how to deal with solar storms, which can cause problems for satellites and (in extreme cases) lead to power and communication blackouts on Earth.
*Perhaps signalling that NASA has finally given up its quest to turn everything into a strained acronym.