OCT 2018


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OCTOBER 2018 78 CompositesWorld FOCUS ON DESIGN door, had to be included, because the satellite has to be main- tained close to room temperature during transport, and some- times in a nitrogen atmosphere depending on the types of instru- ments on board. Hood's team and PEI turned to several software tools for the container's design and composite materials selection. CAD software PTC CREO (previously known as Pro/Engineer) from PTC (Needham, MA, US) allowed solid modeling for establishing the container shape and dimensions. FEMAP finite element analysis (FEA) software from Siemens PLM (Plano, TX, US) was used for pre- and post-processing, and NX/NASTRAN software, also from Siemens PLM, was used as the solver for the FEA model. e modeling software enabled static, quasi-static and modal (natural frequency) analyses, and determination of maximum dynamic loads and stresses due to transportation loading environments, enabling safety considerations in the design. e software's buckling eigenvalue solution module and classical engineering equations helped PEI ensure that potential stress levels would be within allowable limits for the container's laminate architec- ture, which would consist of cored fiberglass sandwich panels. Also, dynamic displacement of the satellite and its turnover fixture were determined to ensure adequate clearance to the container's interior walls. Building Galileo e model results showed that a structure with overall dimensions of 11.5m long by 4.7m wide by 4.3m high, with a "lid" that was 7.7m long by 4.7m wide by 3.9m high, would meet the require- ments and accommodate the GEOStar-3, with enough room for other larger spacecraft. Steel would be specified for the base frame, with its extended front deck, to ensure compatibility with shipping logistics and to accommodate the weight and motion of the complex satellite turnover fixture, as well as provide mounting points for the vibration isolators. e lid on top of the base frame would be made with cored fiberglass, to provide an air-tight, durable and weatherproof structure with minimal joints, and good insulation value. Plus, the lid could be made on simple tooling to help minimize costs. Ultimately, a two-part lid was designed, says Callahan; this was done for several reasons: "Splitting the lid into a lower and an upper section did several things. It reduced the overhead lifting distance, or height needed to clear the spacecraft, during lid removal. And, having the fixed lower lid bolted to the base frame meant that we could keep the connections to auxiliary equipment within that fixed lower part, to simplify operation." e lower lid would be 1m high, and the upper lid would be 2.8m high; the two would be fastened together with multiple quick-release toggle latches. To facilitate logistics, the upper lid was designed with casters at its lower edges, front and back, so that it could be moved easily when detached. It would also have a man-door to provide access to the interior, for preparation activities (e.g., tie-down, purging with nitrogen) prior to shipping. Hood says, "We would have a weekly telephone conference call to monitor the progress of the design," which was dubbed Galileo (a more elegant name than "Antonov shipping container"). Once PEI completed the FEA, design model and fabrication drawings, they were turned over to Northrop Grumman, where engineers integrated the design database into their product data manage- ment (PDM) system. e design package was delivered to Ershigs engineers following Northrop Grumman review and approval. Ershigs vice president and chief operating officer Steve Hettick says that the project was fairly rigorous, with tight tolerances: "Given the physical properties requirements and dimensional tolerances from the client, including minimum stiffness and Read this article online | Constructing the frame The steel frame under construction at Ershigs. Great care was taken to meet tight dimensional tolerances using a sequential welding plan to control heat and warpage, so that the composite lids themselves would have the correct dimensions. Source | Ershigs

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