NASA is currently developing the X-38 vehicle that will demonstrate the technologies required for a crew return vehicle for the International Space Station. This vehicle will serve both as an ambulance for medical emergencies and as an evacuation vehicle for the manned space station. Control surfaces on the X-38 require high-temperature seals to limit hot gas ingestion and transfer of heat to underlying low-temperature structures to prevent these structures from becoming too hot and possibly causing the loss of the vehicle. Working with the NASA Johnson Space Center, the Seals Team at the NASA Glenn Research Center completed a series of tests to characterize baseline seal designs for the rudder/fin interfaces of the X-38. The structure of the rudder/fin assembly and its associated seals are shown in the following illustration.
Left: Temperature exposure of X-38 seals at 1900 °F. Right: Seals before and after 1900 °F temperature exposure.
Glenn performed room-temperature compression tests to determine load versus linear compression, unit loads, contact areas, stiffness, and resiliency characteristics for as-received and temperature-exposed seals. The temperature-exposed seals were stiffer and less resilient than the as-received seals, but the measured unit loads and contact pressures for both conditions were below the limits that Johnson had set as goals for the seals. In the rudder/fin seal location, the seals are in contact with shuttle thermal tiles and are moved across the tiles as the rudder is rotated during re-entry. Low seal unit loads and contact pressures are required to limit the loads on these tiles and minimize any damage that the seals could cause.
Flow tests were conducted on the seals under ambient temperatures to examine their leakage characteristics at different compression levels and gap sizes in both the as-received condition and after temperature exposure. Glenn measured seal flow rates 4.5 times higher than Johnson's preliminary flow goal. On the basis of this finding, Glenn recommended that more detailed thermal analyses be run to account for flow through the seals and to reassess the maximum seal temperatures. Johnson subsequently performed additional analyses that showed that the higher leakage flow would not cause a significant increase in seal temperatures.
Glenn's tests have identified several areas where the X-38 seals have met Johnson's goals and other areas where future work should be completed to ensure that the proper final seal selection is made. Glenn and Johnson are currently defining what additional work needs to be done to develop the final rudder/fin seal design for the X-38 vehicle.
Find out more about this work:
Structural seals and thermal barriers
High-temperature, flexible, fiber preform seal
Glenn's Mechanical Components Branch
Dunlap, Patrick H., Jr.; Steinetz, Bruce M.; and Curry, Donald M.: Rudder/Fin Seal Investigations for the X-38 Re-Entry Vehicle. NASA/TM--2000-210338/REV1 (AIAA Paper 2000-3508), 2000. http://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?2000/TM-2000-210338-REV1.html
Glenn contacts: Patrick H. Dunlap, Jr., 216-433-6374, Patrick.H.Dunlap@grc.nasa.gov; and Dr. Bruce M. Steinetz, 216-433-3302, Bruce.M.Steinetz@grc.nasa.gov
Authors: Patrick H. Dunlap, Jr. and Dr. Bruce M. Steinetz
Headquarters program office: OAT
Programs/Projects: X-38
Last updated June 22, 2001, by Nancy.L.Obryan@nasa.gov
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