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Machine Design

Scanning for Ideas: Arming the Space Station?

The International Space Station will soon be getting a pair of robotic arms called the Special Purpose Dextrous Manipulator.

The device, (nicknamed Dextre), was built by MDA in Canada (www.
), the same company that built the Space station’s 17-meter long Canadarm and Mobile Base, a work platform and storage area for the arm and now the arms. Dextre will work with these two to maintain and service the station. Dextre will handle complicated and delicate tasks, eliminating the need for many space walks.

Dextre resembles a human in that it has a central torso that pivots at the waist and a pair of shoulders, each supporting an arm. Each arm has seven joints, making it flexible and versatile. (In all, the robot has 15 DOF.) To prevent collisions between the arms, only one can move at a time. To add stability, the arm that isn’t going to be used can be anchored to the station at one of several stabilization points. At the end of each arm is the Orbital Replacement Unit/Tool Changeout Mechanism. It incorporates lights, a pair of parallel retractable jaws to grip payloads and tools, a black and white camera, and a retractable and motorized socket wrench for bolting and unbolting components. The lower torso also has a pair of panning and tilting color cameras which let astronauts and those on the ground monitor the arm which is usually out of direct sight.

The 3.5-meter tall robot weighs about 3,656 lb and will be able to move and manipulate 1,320-lb (600 kg) payloads. It will consume an average of 600 W of power and up to 2 kW at peak power. And when moving payloads, it will have a stopping distance of about 0.15 m.

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