High Gain Antenna System Deployment Mechanism Integration, Characterization,  and Lessons Learned Fil Parong*, Blair Russell**, Walter Garcen**, Chris Rose+, Chris Johnson** and Craig Huber** Abstract The integration and deployment testing of the High Gain Antenna System (HGAS) for the Global  Precipitation Measurement mission is summarized. The HGAS deployment mechanism is described. The gravity negation system configuration and its influence on vertical, ground-based deployment tests arepresented with test data and model predictions. A focus is made on the late discovery and resolution of a potentially mission-degrading deployment interference condition. The interaction of the flight deployment  mechanism, gravity-negation mechanism, and use of dynamic modeling is described and lessons learned  presented.  Introduction  During testing and integration of the High Gain Antenna System to the core Global Precipitation  Measurement (GPM) spacecraft, a potential deployment hardware interference issue was discovered. A release mechanism firing order change along with trimming a structurally critical bracket was chosen as a solution to increase clearance. A dynamic software model was built that predicted the worst-case, on-orbit deployment path of the HGAS. The model showed that the firing order change and the material removed from the HGAS hardware provided sufficient clearance margin for a successful deployment. GPM Mission Overview The GPM core spacecraft will carry a high gain antenna system to provide command and control  communications as well as a science data downlink through the Tracking and Data Relay Satellite System (TDRSS). The GPM mission is an international network of satellites that will provide the next-generation global observations of rain and snow. The GPM mission deploys a “core” satellite carrying an  advanced radar/radiometer system to measure precipitation from space and serves as a reference  standard to unify precipitation measurements from a constellation of research and operational satellites. The GPM team, initiated by National Aeronautic and Space Administration (NASA) and the Japan  Aerospace Exploration Agency (JAXA), comprises a consortium of international space agencies. The GPM Core Spacecraft is qualified and scheduled to launch in late February 2014. [http://pmm.nasa.gov/GPM]  HGAS Configuration and Design The assembled HGAS system, shown in Figure 1, has a mass of 95 kg (210 lbm), including 24 kg (52  lbm) for the gimbaled antenna assembly. When stowed, it occupies a roughly 2.8 m x 1.0 m x 0.9 m (110in x 39 in x 35 in) volume, and deploys 3.6 m (140 in) from its base. For antenna pointing, the GPM HGAS employs a two-axis gimbal configuration. Due to field-of-view  requirements and packaging limitations, the HGAS boom assembly consists of two boom sections with shoulder and elbow hinges that contain coaxial deployment springs and dampers. A synchronization  *NASA Goddard Space Flight Center, Greenbelt, MD **Stinger Ghaffarian Technologies Incorporated, Greenbelt, MD +Vantage Systems Incorporated, Greenbelt, MD /g51/g85/g82/g70/g72/g72/g71/g76/g81/g74/g86/g3/g82/g73/g3/g87/g75/g72/g3/g23/g21/g81/g71/g3/g36/g72/g85/g82/g86/g83/g68/g70/g72/g3/g48/g72/g70/g75/g68/g81/g76/g86/g80/g86/g3/g54/g92/g80/g83/g82/g86/g76/g88/g80/g15/g3/g49/g36/g54/g36/g3/g42/g82/g71/g71/g68/g85 /g71/g3/g54/g83/g68/g70/g72/g3/g41/g79/g76/g74/g75/g87/g3/g38/g72/g81/g87/g72/g85/g15/g3/g48/g68/g92/g3/g20/g23/g16/g20/g25/g15/g3/g21/g19/g20/g23 45