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NASA’s Space Shuttle taking off (photo courtesy of NASA/Sandra Joseph and Kevin O’Connell)
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A NASA vendor approached B.A.G. Corp. needing bags designed to meet requirements for the handling and disposition of NASA’s Space Shuttle solid rocket fuel, which is used in the Reusable Solid Rocket Motor (RSRM). The containment of out-of-place propellant, including excess uncured propellant and trimmings off the cured propellant, is mandatory for the safety and protection of all who work in this manufacturing process. Due to the highly explosive nature of the propellant, a Type C groundable container was chosen.
B.A.G. Corp.’s Technical Service Group (TSG) designed six sizes, ranging from 5 to 114 cu ft, of this specialty Super Sack container to accommodate the varying amounts of the out-of-place propellant. The largest of these is a round, swimming pool–shaped, 112-in. diam. by 24-in. tall bag. This container was designed to handle 2000 lb with a 5:1 safety ratio. The smallest sized bags are used throughout the process to contain all processing materials that might be contaminated with the propellant.
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112-in.-diam Pactainer ED groundable super sack designed for NASA’s space shuttle
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All designs are constructed with the Pactainer ED groundable fabric necessary for the extremely flammable atmosphere in which the propellant, in the form of a hard, rubbery substance, is handled. Once the propellant has been mixed and cast into a steel form, all overage is placed into one of the Super Sack Pactainers for controlled destruction. A Super Sack container made with conductive Pactainer ED fabric must be grounded during fill and discharge and offers reliable protection against the risk of fabric surface electrostatic discharge. The ground connection to any one of the six ground tabs allows static charges, which could have accumulated to the minimum ignition energy (MIE) level required to produce a catastrophic spark, to be safely carried away from the bag to ground. The filled bags are removed to an isolated area where they are placed in a high-energy material burn pit for a controlled burn.
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Solid rocket booster in a vehicle assembly building (photo courtesy of NASA)
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The Pactainer ED fabric contains conductive tapes that are woven into a Faraday Cage configuration that routes static charges to the black conductive film ground tab connected to ground. For applications requiring this fabric to have a one mil polypropylene coating, micropores are melted into the coating over the conductive tapes. This process is accomplished by strategically positioned sparks that ignite along the conductive tapes as the fabric passes through this specially designed equipment. The micropores in the coating are necessary to provide a path for the electrostatic charges to reach the conductive tapes. Additionally, the lift loop webbing contains static dissipating threads that provide a secondary means of charge relaxation, if the bag is separated from ground.
To ensure that each and every Super Sack Pactainer ED container is safe for use, a multi-meter is used to test the conductivity between the two corresponding ground tabs in the top and bottom setting seams by measuring resistance in ohms. Additionally, for the first and last bag of the order, a reading is taken between each pair of the six ground tabs, which are sewn into two corresponding sides of the top and bottom setting seams and two opposite side seams. To be acceptable, the resistance reading must be < 30 MΩ which is significantly better than the 100 MΩ that is required for a bag to be considered an electrostatic conductor. In appreciation for the safer RSRM manufacturing environment provided by these FIBCs, NASA and their vendor recognized B.A.G. Corp. as a space shuttle team member. Details of the process were provided by NASA and the vendor.
B.A.G. Corp. (Dallas, TX) develops and manufactures Super Sack containers, woven polypropylene FIBCs for the shipping, handling, and storing of dry, flowable, and fluid products. The company also produces specialty liners for boxes, drums, and FIBCs. Other members of the B.A.G. Corp. family of companies include: FIBC Recycling Inc., which cleans and reconditions FIBCs in a closed-loop system and disposes of bulk bags in an environmentally friendly manner; and Winzen Film, a specialty film extruder that also produces multifilament thread and webbing. For more information, visit www.bagcorp.com.
