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GPM's Solar Array Wings in Testing
Engineer standing on a ladder setting up the GPM solar array for testing. The –Y wing undergoes modal testing, a type of vibrational testing. The small squares are 59 accelerometers that measure the movement of the array. > Full Image

GPM's two solar array wings that extend to the right (+Y) and left (-Y) of the spacecraft 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.

The solar array wings are comprised of 4 panels each. Recently, the +Y solar panels completed Large Area Pulsed Solar Simulator (LAPSS) testing where the panels were illuminated with bright pulses of light to measure the electrical performance of their photovoltaics. The +Y panels and the previously tested -Y panels are being delivered to the solar array mechanical team for assembly into solar array wings.

Meanwhile, samples, or test coupons, of the same materials used in the solar array's construction are currently undergoing a Life Test for atomic oxygen. Atomic oxygen is the elemental form of oxygen, a single atom created by ultraviolet radiation splitting O2, that does not exist in the lower atmosphere. It is common, however, in space at the altitudes at which GPM will be flying. It reacts readily with certain materials and can cause corrosion on some parts of the solar array. The Life Test determines the rate of corrosion and the effectiveness of mitigation techniques, and is proceeding without incident. The GPM satellite is designed to last three years.

Modal testing, one of the types of vibrational testing, has been completed on the qualification solar array wing, which is identical to the flight model that will be on the spacecraft except that it contains mass simulators instead of solar cells. This is the first step in testing the solar array wings' structural integrity. Next the qualification solar array wing will undergo deployment and stiffness test.