Ready for Launch
Those are the Radiation Belt Storm Probes in the cargo hold of this U.S. Air Force C-17, which arrived at Kennedy Space Center a few months ago. The twin spacecraft were strapped to an Atlas V and are scheduled to launch at 4:07 a.m. Eastern this Friday. The two probes are part of NASA's Living With a Star program, tasked with studying the relationship between the Earth and the sun. The instruments on board will measure the particles in the radiation belt, so that scientists can determine what drives them. You can watch a short video on the probes (where this screencap is from) here.
NASA / Kennedy Space Center