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Expedition Six
Space Chronicles #6

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By: ISS Science Officer Don Pettit

Moving in Space

For clean one-directional movements, it is best to push through your center of gravity [cg], but first, you must know where your center of gravity is. You can readily determine this by gently pushing off from structure and observing the imparted rotation. A more sensitive method is to attempt a pure rotation along one axis. If the direction of your push-force is not in a plane perpendicular to the axis and through your cg, you will incite a rotation in more than one axis. By doing this I discovered that for a stretched out bodymy cg is just above the hips. This defines the location of your center of gravity when you translate forward Superman style like we often do in 0g. When you translate, the natural place for your arms is overhead to grab onto and push off from things as they come whizzing by. This is the worst possible place from the physics of pushing and pulling if you want clean movements, for by exerting forces with arms overhead, you invariably impart some unwanted rotations which have to be compensated with ever more pushes and pulls, giving an awkward look to the whole movement. To cleanly translate, I found it is best to keep your hands by your hips when exerting forces and boldly go headfirst. This way your pushing and pulling is directed through your body's center of gravity and gives nice controlled motions without unwanted rotations.