OCT 2018


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79 Composite Container Protects Satellites strength, it was necessary to use resin infusion methods, rather than open molding methods typical for one of our tank products, for instance." e model called for cored panel construction over the lid's flat surfaces, with seven separate panels for the larger upper lid, and four panels for the lower lid. Northrop Grumman specified that the core would be beveled at a 45° angle towards the panel edges, or flanges, at the corners and edges, explains Hettick: "is provided a solid fiberglass laminate along the panel flanges for a much easier and more efficient way to join the panels together." e panels were made with multi-ply skins consisting of E-glass knitted biaxial fabric (E-LTM 1208), chopped strand mat, and woven roving, supplied by Vectorply Composites (Phenix City, AL, US), Owens Corning (Toledo, OH, US) and ValuTex Rein- forcements (Washington Court House, OH, US), respectively. Four plies totaling 0.125 inch thickness make up the face sheets over the core; plies are extended beyond the beveled core, and then built up with 14-17 additional plies of Vectorply Compos- ites' biaxial glass to form the monolithic panel edge flanges, for a minimum flange thickness of 17.8 mm. e core is a 76-mm-thick BALTEK (Sins, Switzerland) SB 50 balsa wood with a density of 109 kg/m 3 . Hettick says balsa was chosen because it provides good stiffness without a significant weight penalty, and good insu- lating value. e resin is a Derakane Class 1 fire-retardant vinyl ester (510-B) from Ashland (Columbus, OH, US). Panels were vacuum infused on an airtight flat table mold and cured at room temperature. To assemble and join the panels for the lower and upper lids, they were braced and aligned in metal holding jigs to maintain tolerances, while the panel edges were secondarily bonded together. "We wet out glass mat and woven roving to laminate the edges together," says Hettick. He adds that Ershigs built the steel base frame as well. Truck, plane and barge Hood says that once all of the interior fitments were ready to go, including the turnover fixture (dubbed Big Blue, because of its blue paint), fabricated by D.L. George & Sons (Waynesboro, PA, US), a load proof test was conducted using weights that totaled twice the design weight of the satellite: "We loaded it onto a truck, drove it around, and monitored its performance, and it passed with flying colors." So far, the shipping container has been used three times to successfully transport spacecraft via the Antonov cargo plane to French Guiana. On the most recent trip, the container was barged back to the US and then trucked to Dulles. Concludes Hettick: "While this project was a specialty item for us, it was a fun project, as well as a challenge, because the speci- fied tolerances were fairly tight for the size of the part." Hood adds: "We had the right team of people for this job, and we were very satisfied with the results." Sara Black is a CW senior editor and has served on the CW staff for 19 years. Fiberglass laminate This photo of the lower lid, which is fixed to the steel base, shows the cored panel configuration, and the beveling of the core towards the panel edges. This provided a solid fiberglass laminate along the panel flanges for a much easier and more efficient way to join the panels. Source | Ershigs Bracing for tight tolerances The tight tolerances required bracing of the upper lid panels during assembly and joining. Source | Ershigs

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