Crabs have a strong exoskeleton that protects them from predators and water pressure, as well as providing support for their internal muscles and organs.
Rockets and shuttles sent into space also have a strong out shell, designed to with stand the negative pressure of space, remain airtight and to protect the inhabitants; both people and technology. Some rockets have been built using a monocoque technique, using the strong 'exoskeleton' as its structure to bear the internal load.
I built on this crab image (above), which I originally made as just an element for a larger image, to create a space shuttle/crab hybrid based on the similarities in their structure, and the importance of their protective shell. As always I may add to this to perhaps make it more clear that its to do with the external structure. I'm also not too sure about the background and if there's more I could do with that, although it's nice to use some brighter colours for once; can't seem to escape the dark blackness of space/underwater with some of the images I've been doing recently! Over and out.