Author Topic: International Space Station Powered Bolt Nut Anomaly and Failure Analysis Summar  (Read 1457 times)

Offline rdale

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    A key mechanism used in the on-orbit assembly of the International Space Station (ISS) pressurized elements is the Common Berthing Mechanism (CBM). The mechanism that effects the structural connection of the CBM halves is the Powered Bolt Assembly. There are sixteen Powered Bolt Assemblies per CBM. The CBM has a bolt which engages a self aligning Powered Bolt Nut (PBN) on the mating interface; see Figure 1. The Powered Bolt Assemblies are preloaded to approximately 19 kilo pounds (KIPs) prior to pressurization of the CBM. The PBNs mentioned below, manufactured in 2009, will be used on ISS future missions. An on orbit functional failure of this hardware would be unacceptable and in some instances catastrophic due to the failure of modules to mate and seal the atmosphere, risking loss of crew and ISS functions. The manufacturing processes which create the PBNs need to be strictly controlled. Functional (torque vs. tension) acceptance test failures will be the result of processes not being strictly followed. Without the proper knowledge of thread tolerances, fabrication techniques, and dry film lubricant application processes, PBNs will be, and have been manufactured improperly. The knowledge gained from acceptance test failures and the resolution of those failures, thread fabrication techniques and thread dry film lubrication processes can be applied to many aerospace mechanisms to enhance their performance. Test data and manufactured PBN thread geometry will be discussed for both failed and successfully accepted PBNs.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100001671_2010000493.pdf

Offline robertross

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That was a fantastic & enlightening read. Thanks for posting this rdale.

I have to wonder though...how does this affect hardware on orbit? If there is concern, I'm hoping easy change-out, like the last MPLM mission where they had to replace a failed bolt, can be effected. Not sure if these are the same (2007 batch), or a completely different design.

One thing: HSF needs have driven another new manufacturing process to better control end product reliability.
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