Lessons Learned in the Flight Qualification of the S-NPP and NOAA-20  Solar Array Mechanisms  Daniel Helfrich * and Adam Sexton ** Abstract  Deployable solar arrays are the energy source used on almost all Earth orbiting spacecraft and their release  and deployment are mission-critical; rigorously testing them on the ground is both essential and quite  difficult. The 8-meter-long deployable arrays flown on two sequential NASA weather satellites were each  comprised of three rigid panels over 2.5 meters wide and almost 2 meters tall. These large panels were  deployed by hinges comprised of stacked constant-force springs and eddy current dampers and were  restrained through launch by a set of four releasable hold-downs using shape memory alloy release  devices. The ground qualification testing of such unwieldy deployable solar arrays, whose design was  optimized for orbital operations, proved to be quite challenging and provides numerous lessons learned. A  paperwork review and follow-up inspection after hardware storage determined that there were negative  torque margins and missing lubricant; this paper will explain how these unexpected issues were overcome.  This paper will also provide details on how the hinge subassemblies, the fully-assembled array, and  mechanical ground support equipment were subsequently improved and qualified for a follow-on flight with  considerably less difficulty. These two solar arrays built by Ball Aerospace Corp. for the Suomi National  Polar Partnership (S-NPP) satellite and the Joint Polar Satellite System (JPSS-1) satellite (now NOAA-20)  were both successfully deployed on-obit and are performing well.  Introduction  One of the first key events on larger spacecraft is the mission-critical deployment of the solar array,  providing electrical power to sustain the mission for its duration. Prior Ball Aerospace satellites used smaller  solar arrays that could stow around the body of the satellite structure. Embarking on a new design effort  required the design and qualification of new solar array mechanisms, composite panels to support solar  cells (substrates), and the ground test equipment. During the S-NPP lifecycle, the new mechanisms  encountered design and test issues which included excessively stacked constant-torque springs, incorrectly  processed parts, variable resistive torque profile through the range of motion of the hinge, unplanned  resistive torques, inadequate harness characterization, inability to complete subsystem-level vibration  testing, and issues with subsystem-level deployments. Design flaws identified from the S-NPP program  were addressed during the JPSS-1 program and provided for much smoother delivery of mechanisms to  the subsystem assembly, however lingering issues with the gravity-negation deployment system design  and usage in different configurations provided some new challenges to overcome.  Sources of Driving Mechanisms Requirements  The solar array for S-NPP was required to be compliant with MIL-A-83577B, “Moving Mechanical  Assemblies for Space Launch Vehicles (MMA),” and with GSFC-STD-7000, the “GEVS” standard, an  acronym for Goddard Environmental Verification Standard. Both of these require margins on the driving  torques to assure robust mechanism performance. GEVS mandates the use of factors of safety on the  sources of drag torque in completing the analysis. When JPSS-1 began, the standard known as the “Gold  Rules,” GSFC-STD-1000, was also implemented, driving the project towards more rigorous solar array  *NASA Goddard Space Flight Center, Greenbelt, MD ** Ball Aerospace Corporation, Boulder, CO Proceedings of the 44th Aerospace Mechanisms Symposium, NASA Glenn Research Center, May 16-18, 2018 NASA/CP—2018-219887 389