When the Space Shuttle is launched from Launch Complex 39, it produces extreme heat, abrasion, and chemical exposure that severely stresses protective coatings on nearby equipment and structural components. The inorganic zinc (IOZ) coatings used to protect the structural steel from salt corrosion cannot withstand this abuse in several areas on the pad. After each launch, surfaces located at the 95-foot level, the interface tower, the hydrogen bridge structure, and the east stair tower receive a lot of heat and burnoff of the IOZ. These areas require expensive refurbishment after each launch to protect the structure, which accounts for a majority of the overall structural work costs.
As a possible solution to this problem, ablative-type silicone-based coatings were investigated based on the success of these types of materials used on other systems in the blast zone at the pad. At that time, the approved silicone ablative coatings were only in a trowelable form that also required the application of sensitive silicone primers to the surfaces for adhesion purposes. The study focused on the development and approval of new-generation silicone coatings that were not only sprayable but self-priming as well. The ability to spray coat rather than trowel-apply surfaces would allow the application of these materials to large surface areas with relatively low labor costs.
In conjunction with several industry partners, these new-generation materials were formulated, sprayed, evaluated, and approved for use on Launch Complex 39 structures. These silicone ablative materials held the promise of forming a tough surface film when subjected to intense heat and eroded only slightly from the effects of a Shuttle launch. Even though these ablative materials would initially cost more to install than the IOZ coatings, the time and effort saved by not having to recoat after each launch would allow payback in a relatively short time. The reduction in refurbishment after each launch would also reduce turnaround time for use of the launch pad structures and systems.
For this effort, the materials were sprayed onto steel test panels and mounted on a carrier plate. This plate was attached to the Mobile Launcher Platform deck (see the photo). After exposure to launch, the panels were removed and evaluated for approval. Based on the results of these tests, several materials were approved for use at KSC launch facilities and will be included in the current revision of KSC-SPEC-C-0006.
As part of a major refurbishment to Launch Complex 39B in 1994, an approved ablative silicone was applied to areas of the 95-foot level and the weather protection system in preparation for STS-64. Following that launch, the ablative coating was found to have performed very well. Since that time, the material has resisted the effects of five more launches and has significantly reduced launch damage, associated refurbishment costs, and turnaround time. The materials have also been applied at Launch Complex 40 at Cape Canaveral Air Station with similar successful results. Details of the laboratory testing and exposures at Launch Complex 40 can be found in several publications under document numbers FAM 92-2150 and FAM 93-2057. Results of this work were also documented in a manufacturer's newsletter in 1994 and in the Journal of Protective Coatings and Linings of the Steel Structures Painting Council in July 1995.
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Contact: L.G. MacDowell, LO-MSD-1M, (321) 867-3400
