Engineers Prepare the GPM Solar Array for Testing. The –Y wing prepares to undergo modal testing, a type of vibrational testing. Therefore small squares are 59 accelerometers that measure the movement of the array. Also GPM’s two solar array wings that extend to the right (+Y) and left (-Y) of the spacecraft. And are currently undergoing assembly and testing at Goddard Space Flight Center, Greenbelt, Md. The solar arrays provide all the electrical energy for the satellite, and must survive flying in Earth’s thin upper atmosphere at an altitude of 407 km (253 miles), where they will be subjected to small drag forces and exposure to corrosive atomic oxygen