Charles W. Williams is a graduate of the University of North Alabama, Florence, AL in 1966 with B.S. degrees in Chemistry and Math. Immediately following graduation, he worked for eight years with Hayes International Corporation as a support contractor to the Marshall Space Flight Center, in Huntsville, AL. Mr. Williams joined Martin Marietta (now Lockheed Martin) in 1976 to support the Design, Development, Test and Evaluation phase of the Space Shuttle External Tank Thermal Protection System (TPS). Following the successful launch of the first vehicle, Mr. Williams was tasked with the assignment to improve performance and reduce weight of the External Tank TPS. Over 1000 pounds weight savings were realized beginning with ET-12 through the next several tanks due to development of higher performance materials and refinements in flight environments. Beginning with the EPA phase out of CFC's, used as blowing agents in foams, efforts were focused on development of materials compliant with environmental laws and regulations. Research work over the last six years has dealt with continued issues relating to increased TPS weight reduction while at the same time addressing the imminent phase out of HCFC's used extensively as blowing agents in TPS foam systems.

Presentation Topic : Modifications to the Space Shuttle External Tank Thermal Protection System to Comply with the New Environmental Laws

By: Charles W. Williams

Lockheed Martin at NASA's Michoud Assembly Facility in eastern New Orleans manufactures the External Tank (ET) for the Space Shuttle. The phaseout of ozone depleting substances (ODS) under EPA regulations has had a major impact on ET production. The ET requires a thermal protection system (TPS) to maintain the quality of the cryogenic propellants used to power the Shuttle, provide protection from aerothermal and vehicle plume heating environments, prevent formation of ice on exterior surfaces, and maintain structural integrity. The TPS is a rigid foam that initially used CFC 11, then HCFC 141b, as the chemical blowing agent to provide the critical insulation and cell structure properties. Lockheed Martin and NASA began HCFC 141b replacement efforts far in advance of the upcoming 1/1/2003 phaseout, but no replacement has been found that meets performance requirements. This presentation illustrates issues with which the manufacturers and consumers of insulating foams are faced due to the ODS phaseout program, as well as problems unique to the space program.

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