shuttle orbiter's selection and implementation of an environmentally compliant primer, The

Logistics Spectrum, Apr-Jun 2001 by Hill, Robert, Eichinger, Eric

National Aeronautics and Space Administration (NASA) takes great care to keep the Orbiter in a controlled environment. However, the vehicle cannot escape repeated visits to the Kennedy Space Center launch pad. The launch pad environment is one of the most corrosive environment exposure conditions for Orbiter operations. Orbiter corrosion can largely be controlled by applying an epoxy primer. Unfortunately the industry standard primers contain both carcinogenic hexavalent chromium and high levels of volatile organic compounds (VOCs). Recent environmental regulations make continued use of these primer candidates an issue for worker exposure and VOC containment.

The primer industry is now producing an array of compliant (nonchrome, low-VOC) coatings. Yet, the unique requirements associated with manned space flight make material replacement a sensitive subject. The Orbiter program and the Department of Defense (DoD) is performing a comparative study of compliant primers under the joint DoD/NASA Joint Group on Pollution Prevention (JG-PP). This article summarizes Orbiter's effort to find and adopt a primer that meets strict performance and environmental regulations, and how the effort was facilitated by an ongoing joint DoD/NASA JG-PP task.

Background

After three years of unsuccessful primer evaluations, the Orbiter community was willing to believe that effective environmentally compliant materials were just not available. About that time, the Aerospace Chromate Elimination team identified and discussed a JG-PP primer study which reported very encouraging results on two compliant primers. The Orbiter program contacted the Navy (JG-PP representative), NASA Acquisition Pollution Prevention Program Office (JG-PP working group representative) and Boeing project leads. It learned that one of the effective primers, made by Crown Metro, appeared to meet many Orbiter requirements. Orbiter primer testing was reinitiated using the JG-PP primer and a few others. Orbiter's testing confirmed the JG-PP results and demonstrated the primer met Orbiter specific cryogenic and bonding requirements. The JG-PP primer and two other effective products (from Deft Coatings) were candidates for implementation.

Implementation

Implementation of a new material on the Orbiter is never easy, given the safety concerns associated with manned space flight, especially in this case where environmentally compliant materials are new and there is little if any field data. Once again the JG-PP effort provided assistance. By this time JG-PP was applying the Crown Metro primer to F-15s, F-18s and other military system hardware. JG-PP provided early field data and a promise that they would evaluate their coatings for about four years and report results.

This allowed Orbiter to select the Crown Metro primer for implementation and ultimately receive NASA approval to use it.

When the primer was approved, Orbiter prepared a new material specification and detailed application instructions. One problem, though, was finding a place on which to apply it. Orbiters are no longer being manufactured. Plus, Orbiter design engineers were very reluctant to depart from the industry standard that had given them over 20 years of effective corrosion protection. Finally, one designer allowed the new primer on the trailing edge of the wing. The parts, called flipper doors or elevon cove seals, would be alternatively coated with the new and old primer as depicted in Figure 1.

Finally, the approvals were complete, the engineering paperwork implemented the primer, and all that was left to do was apply the primer to the hardware. Orbiter engineering was prepared for problems associated with using the new primer, but not the problem that they encountered with the old primer. The new primer was purchased within a week and applied without any problems or incidents the following week. Refer to Figure 2. The chromated primer had to be specially ordered and took several months to arrive, thus delaying half of the flipper doors.

Results

The Orbiter now has some of its hardware relying on non-chrome, lowVOC technology. And, the sentiment within the design community is slowly shifting toward accepting the new primer. The hope is that after two flights there will be confidence that the two primers can be used interchangeably. This would greatly reduce the amount of paperwork that would need to be changed to fully implement the new primer. It is widely agreed that the cost of changing every design requirement for the old primer is prohibitive. Full implementation and configuration control are expected to be the future challenges associated with using the environmentally compliant primer. Perhaps the JG-PP will be helpful with these future challenges, given their experience with making "block changes" to implement one material over another at a very high level. Whatever happens, the Orbiter has reduced its dependence on a hazardous, potentially obsolete material which makes hardware delivery safer and more timely.