SIMULATION, DEVELOPMENT, AND FIELD MEASUREMENT VALIDATION OF AN ISOLATION SYSTEM FOR A NEW ELECTRONICS CABINET IN THE SPACE SHUTTLE LAUNCH ENVIRONMENT WITHIN THE MOBILE LAUNCH PLATFORM
Recent replacement of the cabinet-mounted low voltage power switchgear within the Space Shuttle Mobile Launch Platform (MLP) has necessitated the need for a dynamic analysis and the development of a 6 degree of freedom isolation system. This is required due to the addition of electronic sensing and control components in modern electronic switchgear and the harsh vibration environment experienced within the MLP during a launch of the Shuttle. The isolation system is required to isolate the switchgear to prevent the spurious tripping of breakers that would compromise Programmable Logic Control (PLC) operation during launch. An added benefit of the isolation system is that it provides vibration isolation during the Shuttle’s approximately three mile journey between the Vehicle Assembly Building (VAB) and either of its two launch pads. Initially, a broadband launch environment PSD input was defined. Then, a rigid body 6 degree of freedom dynamic analysis accounting for 3-dimensional performance was performed in order to optimize the isolation system attributes including parametric output and mounting arrangement within the existing structure. The isolation system was then designed, built, and integrated within the MLP after making some structural modifications to the MLP support steel. Finally, broadband dynamic measurements were made during an actual Shuttle launch in order to verify the effectiveness of the isolation system and to validate the predictions of the analysis. Measurements made during the launch of STS-115 on September 9, 2006, have affirmed the effectiveness and the predicted performance of the isolation system.
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TAYLOR DEVICES HERMETIC DAMPERS DESCRIPTION, APPLICATIONS, AND DESIGN
This unique damper was developed during the 1980’s for use on platforms based in outer space. NASA and the U.S. military had experienced difficulties over the years with all types of oil filled products in space. Conventional sliding surfaces that were sealed acceptably on earth proved unacceptable for spacecraft use. The reason was simply that even the tiniest amount of fluid weepage past conventional seals turns into a dense fog in a vacuum, contaminating optics and electronic systems.
Taylor Devices’ solution was to develop a damper that used a flexural seal – thus sealing by non sliding methods. The seal itself was a so-called metal bellows made by laser welding thin discs of stainless steel into a bellows configuration. For maximum reliability, a two-ply disc configuration was used, with each disc comprised of two sheets of .003 inches thick 17-7 stainless steel. The successful use of metal bellows to seal gases in space was well established, but the Taylor Devices’ damper design was the first to use this technology to seal fluids. To insure absolute zero leakage, each finished bellows assembly is placed in a vacuum chamber and filled internally with helium gas. A mass spectrometer is then used to search for zero leakage of even individual helium molecules from the completed bellows. Extensive testing by NASA revealed a second design feature of this product – its near zero operating friction. This is simply because the use of non-sliding seals essentially eliminates seal friction. Thus, the Taylor Devices Hermetic Damper provides an extremely high fidelity response to shock and vibration over a frequency band of 0-500 Hz.
This damper proved highly successful, but due to security regulations was not disclosed outside the U.S. space program until 2002. Today, more than 100 satellites are in space using Taylor Devices’ Hermetic Dampers with metal bellows seals. In addition, numerous high altitude military aircraft programs are using the same Taylor Devices’ technology for use in the near space environment on reconnaissance cameras and sensors. Taylor Devices has been awarded six U.S. patents on the design.
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