Thursday, December 18, 2008

Today's word is ... "frangible"

Frangible items are designed to break into fragments, rather than deforming and remaining a single piece.

The space program makes wide use of frangible nuts and bolts as connectors that hold items together until an exact moment when they have to be separated quickly. This quick separation is accomplished with an explosive charge, referred to as a "pyro" (for pyrotechnic device) or an NSD ("NASA Standard Detonator"). The astronaut (or the computer system) throws a switch to activate a certain sequence; the pyro blows and the frangible nuts and bolts that held the item together shatter, allowing the items to separate.

Examples of this in action would be separating the spent solid rocket boosters from the Space Shuttle, releasing a satellite from the Shuttle's payload bay, or even deploying the spring-loaded solar panels on the MER Mars rovers. The frangible nuts and bolts in the picture above are from the Space Shuttle program.

In my mind, the most famous film depiction of pyros was in 2001: A Space Odyssey, when the explosive bolts were used to blow off the EVA pod's door so that Dave Bowman could quickly enter the emergency airlock.

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