Original Date: 04/26/1999
Revision Date: 01/18/2007
Best Practice : Marshall Convergent Coating
During a launch, the space shuttle’s solid rocket boosters (SRBs) are exposed to extreme heat generated by wind resistance and engine exhaust. In the mid-1980s, Marshall Space Flight Center (MSFC) developed Marshall Sprayable Ablator-2 (MSA-2) as an ablative insulation material to protect the SRBs’ forward assembly, systems tunnel covers, and aft skirt. During the MSA-2 process, nine ingredients are mixed with the adhesive and then applied to the desired area. Although effective, MSA-2 had many drawbacks. Each batch was costly and had a five- hour pot life. The application process was often interrupted which ruined some or all of a batch. The tensile strength of MSA-2 was difficult to regulate, and the material tended to come off the SRBs during the flight and especially at splashdown. The cost of investigating this anomaly added to the expense of using this insulation material. In addition, MSA-2 contained two chlorinated hydrocarbon solvents which were harmful to the environment.
The Space Act Agreement fosters the transfer of laboratory technology to real-world applications. In Fall 1993, MSFC teamed with United Technologies’ USBI to investigate an alternative to MSA-2. Using convergent spray technology (CST), they atomized epoxy and filler materials to create an ablative insulation material called Marshall Convergent Coating-1 (MCC-1). This environmentally friendly coating is superior to MSA-2, and consists of 8% hollow spherical glass, 9% cork, and 83% two-part epoxy by weight. During the MCC-1 process, materials are mixed at the point of release from a specialized spray gun at the time of application. This solventless approach prevents interruptions from ruining a pre-made batch. The first SRB flight hardware sprayed with MCC-1 was a left- hand skirt for the Space Shuttle Atlantis (STS-79). The excellent performance during this September 1996 mission led to the full implementation of MCC-1 on all subsequent flights. Virtually no missing MCC-1 has been noted during the post-flight inspections of recovered SRBs.
Besides the SRBs, MCC-1 was used on the U.S. Air Force’s Titan IV payload fairing trisectors and Boeing’s Sea Launch, and has been selected for Boeing’s Delta IV. There is potential to qualify MCC-1 for multi-flight use on the SRBs and to determine if CST can be used on the space shuttle’s external tank as well as other SRB applications. Tested spin-offs of CST include acrylic filled with recycled rubber for roof surfaces on industrial buildings, and epoxy filled with abrasive flint as a skid-resistant coating for the road surfaces of the Bankhead Tunnel and a highway bridge on Interstate 65 in Alabama.
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