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Vertical Tail Sector Seals

Problem: Orbiter vertical tail sector and linear seal cracks have been identified, and there are no spares (100-Mission Certified). Current design has limited life. Vertical tail seals protect adjacent parts from high thermal environment (900 Degrees F). Fleet swapping plan for short term approved. Incoloy 903 was chosen for the base line deal design because of its high strength and its low coefficient of thermal expansion (CTE). Incoloy 903 is extremely susceptible to oxidation at 900F suring re-entry. Formation of microcracks is facilitated by oxidation of the base metal and the presence of bending stresses in the formed sections of the seals. The Pyromark coating does not provide a good barrier for oxidation to the Incoloy 903 base metal, but is used for emissivity purposes.
Solution: Design change to Inconel 718. An oxidation resistant high strength alloy such as Inconel 718 is required to eliminate oxidation, pitting and cracking of the seals. Inconel 718 does not require a coating for oxidation protection. Pyromark coating is required for emissivity purposes. Inconel 718 has a CTE two times more than Incoloy. Inconel 718 is 30% stiffer than Incoloy.
Initial Operation Date: Phase II Upgrade
OV -102 OMM (11/1/98 Thru 6/30/99)
OV -103 STS 97 Flight Date 3/18/99
OV -104 STS 92 Flight Date 1/14/99
OV -105 STS 98 Flight Date 5/13/99
Technology Goal: No New Technologies
Goals Supported: 1) Fly Safely
3) Improve Supportability

Curator: Kim Dismukes | Responsible NASA Official: John Ira Petty | Updated: 04/07/2002
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