"ROBOT: copies cats to eliminate spin in free fall"
The National Aeronautics and Space Administration's "weightless wonder" aircraft will be the testbed this week for a robot that exhibits catlike motion in free fall. The work could one day lead to designs that eliminate the need for retrorockets, gas jets and gyroscopes in satellites and other spacecraft. The robot rotates without angular momentum by changing the length of parts of its body while rotating them in opposite directions, much as a falling cat does. Managing that momentum is the bane of space navigation today, complicating almost every space-based maneuver, introducing unwanted spin that must be compensated for with retrorockets or gas jets. In devising the concept, project leader Gregory Ojakangas, a physics professor at Drury University (Springfield, Miss.), borrowed from a species that flouts the rules of angular momentum. "When you drop a cat upside down, it always lands on its feet, with no spin. It doesn't paddle the air � that would impart spin � it just expands its upper body and rotates it, then contracts its upper body and rotates in the opposite direction," said Ojakangas. "In that sense, ours is not a new idea; nature has been doing it for I don't know how many millions of years."