Advanced in-space repair technologies for reinforced carbon/carbon composite (RCC) thermal protection system (TPS) structures are critically needed for the space shuttle Return To Flight (RTF) efforts. These technologies are also critical for the repair and refurbishment of thermal protection system structures of future Crew Exploration Vehicles of space exploration programs. The Glenn Refractory Adhesive for Bonding and Exterior Repair (GRABER) material developed at the NASA Glenn Research Center has demonstrated capabilities for repair of small cracks and damage in RCC leading-edge material. The concept consists of preparing an adhesive paste of desired ceramic in a polymer/phenolic resin matrix with appropriate additives, such as surfactants, and then applying the paste into the damaged or cracked area of the RCC composite components with caulking guns. The adhesive paste cures at 100 to 120 °C and transforms into a high-temperature ceramic during simulated vehicle reentry testing conditions.
A number of plasma torch and arc-jet tests were carried out to evaluate the crack repair capability of GRABER materials for RCC composites. Cracks were introduced in RCC specimens by machining slots and filling them with GRABER repair compound. Six RCC specimens with 0.035- and 0.064-in. machined slots were repaired with GRABER, and the repaired specimens were tested in the arc-jet facilities at the NASA Johnson Space Center and the NASA Ames Research Center for approximately 15 min. All six samples survived the tests without any burn through. This photograph shows the front view of a crack-repaired RCC specimen after arc-jet testing. The GRABER-based repair materials stopped the plasma flow through the specimen and prevented any damage. It is important to point out that unrepaired RCC specimens with a similar type of damage will have significant burn through because of plasma oxidation, which transforms the small crack region into a large hole, leading to catastrophic damage.
GRABER-repaired RCC specimen after arc-jet testing. The crack was 1.5 in. long and 0.035 in. wide. The specimen survived simulated reentry testing.
GRABER-based materials have multifunctionality and versatility for a wide variety of repair applications. They have been used as adhesives and sealants in the patch/plug concept and have performed exceptionally well in plasma-torch and arc-jet testing. These materials have also shown exceptional plasma performance as inner-to-outer mold line materials for a filled-wing concept. The materials are being used to prepare adhesive patches and flexible ceramic prepregs using different types of fabrics to repair large damaged areas. Further development and testing are underway to optimize the materials’ properties and extend the application temperatures.
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Materials Division highlights, 2004
Materials Division highlights, July 2004
On-orbit shuttle repair takes shape
QSS Group, Inc., contact: Dr. Mrityunjay Singh, 216-433-8883, Mrityunjay.Singh@grc.nasa.gov
Glenn contact: Dr. Andrew J. Eckel, 216-433-8185, Andrew.J.Eckel@nasa.gov
Authors: Dr. Mrityunjay Singh and Tarah P. Shpargel
Headquarters program office: Space Operations Mission Directorate
Programs/Projects: Space Shuttle, RTF
Last updated: July 19, 2005 1:36 PM
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