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tech track papers

Categories: 2016, Launch

Cryogenic and Hypergolic Fuel & Oxidizer Sealing in Launch Vehicles

Liquid propulsion system in launch vehicles can be based on either cryogenic or hypergolic fluids. Sealing these fluids in pressurized conditions is very challenging. In cryogenic propulsion system, some fuels and oxidizers (e.g., liquid hydrogen and liquid oxygen) are stored in storage tanks well below cryogenic temperatures (-238°F/-150°C) all the way down to -424°F/-253°C. Conventional seals like o-rings and other elastomer seals cannot handle these extreme temperatures. As a result, these seals leak. As the fuels and oxidizers are transported from external tanks to combustion chamber, these cryogenic fluids come in contact with series of pumps, compressors, valves, ducts, joints and manifolds. These areas too need to have very robust sealing. Seals fitted inside POGO suppression Device (PSDs) have to be able withstand crack due to oscillations in the ducts carrying liquid oxygen and hydrogen to the rocket engines. When hypergolic fuel like monomethyl hydrazine (MMH) and oxidizer like nitrogen tetroxide (NTO) are used instead of cryogenic fluids, the seals that come in contact must be able to handle these very corrosive and aggressive fluids. Hence, the selection of seals and sealing material plays a very important role. Several parameters like lower temperature limit, thermal cycling, wide temperature range, chemical compatibility, seals cleanliness, low friction and wear has to be considered during the seal selection and design. Elastomer seals, polymer seals and metal seals behave differently in these environments and can influence the geometry and surface finish of grooves and glands in which they sit. Correct selection of seals around the given sealing environment is important for cost and performance but, more importantly, critical to mission safety. This presentation will talk about competitive advantages of spring-energized polymer seals vs. elastomer and metal seals in cryogenic and hypergolic sealing applications in launch vehicles.

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Author: Kha Le
Topic: Launch