Monday, September 20, 2010

Rocket Ships Are Tensegrities

NASA's Centaur is a rocket stage designed for use as the upper stage of space launch vehicles. It is essentially a smaller version of the Atlas, that is, a lightweight "stainless steel balloon" tanks whose structural rigidity is provided solely by the pressure of the propellants within. To keep the tanks from collapsing prior to propellant loading, they were either kept in "stretch" or pressurized with nitrogen gas. As such, these rockets are pneumatic structures, and so they qualify as being tensegrities.

Pneumatics in general is the study, application and use of pressurized gas in structures and manufactured devices, usually to affect mechanical motion. Pneumatics is significant to tensegrity structural study as the pneumatics of pressurized, inflatable, flexible membranes are considered as an ideal model of a prestressed tensegrity structure. The membrane plays the role of the tension network while the isolated, rapidly moving molecules of the compressed gas play the role of the compression struts. The two classic examples are balloons and pneumatic tires.

Pneumatics are also used in dynamic tensegrity structures to extend and collapse adjustable length struts. Sterk has written about pneumatics in dynamic structures here.
Of course, such pneumatic rocket ship structures are not to be confused with the growing literature on deployable tensegrities in space, such as "Concept of Inflatable Tensegrity for Large Space Structures" by Hiroshi Furuya, Makiko Nakahara†, Satoshi Murata‡, Daisuke Jodoi, Yuzuru Terada, and Keiki Takadamak from the Tokyo Institute of Technology, Yokohama, Kanagawa, Japan, presented at the 47th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference held 1 - 4 May 2006 in Newport, Rhode Island, here. The former are for blasting off into space, the latter are for being in space.

Many thanks to sanman for reminding me of the importance of pneumatics: I updated the page in the wiki. Also, for those who missed it, check out the pneumatic girders made by Tensairity.


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