Upgraded space robot will lend a hand

James Oberg NBC News space analyst

HOUSTON - The Canadian-bulit Dextre robot that the shuttle Endeavour's crew delivered to the international space station looks for all the world like an extra for one of the "Terminator" movies — except for the kid's beanie attached to its head.

That giggle-provoking hat may spoil the fearsome effect of Dextre's muscular shoulders and multijointed arms and hips, bristling with gadgets and canisters. But it's actually a cool piece of space hardware that gives the robot special powers. The "beanie" is the attachment point between Dextre and the muscular robot arm now attached to the space station.

Astronauts started putting Dextre together Thursday night during the Endeavour mission's first spacewalk, and the assembly work will continue over two more spacewalks. Robotics experts still have to resolve a problem with Dextre's power system — but the result will be well worth the trouble. Once Dextre is on the job, the international space station's crew will have an upgraded robotic assistant that is far more valuable than the sum of its parts.

Even before Dextre's arrival, the space station's arm has served as much more than just an arm. It's really a robotic biped with arms at both ends, each topped with a grapple fixture. The robot performs its duties by "walking" across the outer surface of the station, grabbing onto handles one after the other. Each grapple fixture contains plugs and sockets for power, data, command and video links between the control post and the free-roving robot.

But the twin arm's powers are limited: The two grapple fixtures are fairly clumsy mechanisms, not much more flexible than an old Hollywood pirate’s hand-replacing hook. They can attach to prepared anchor points, or to movable modules (even very big ones) and astronaut work platforms (some quite small). But they can’t “pick up” anything else.

The 2,860-pound (1,300-kilogram) Dextre will change all that. It will revolutionize space station external maintenance and servicing operations by becoming the "business end" of the station's robotic arm — and much more.

Dextre will provide precise manipulation capabilities for external work on the station — without the presence of spacewalking astronauts. Its vaguely humanoid architecture has two seven-jointed arms plus "hands," outfitted with a rudimentary nervous system. These grapplers do not have "fingers" as fine as a human's, but the grippers can hold a wide array of tools and can take hold of small objects such as cables, levers or thermal blankets.

Each of Dextre's arms extends from a "shoulder," and has a chain of positional joints: shoulder roll, shoulder yaw, shoulder pitch, elbow pitch, wrist pitch, wrist yaw, and wrist roll. The string of rotating joints can manipulate the far end with millimeter-level accuracy.

Each wrist has lights and a high-resolution black-and-white TV camera. And at the very end is a completely new device, a force sensor that measures just how much push the arm is imparting to the object of its attention. This will allow operators inside the station (or on the ground) to tighten bolts "just enough," or to tug hard enough but not too hard, when manipulating the arms.

The "hand" is known technically as the Orbital Replacement Unit/Tool Changeout Mechanism (OTCM). It consists of a set of parallel retractable jaws, which serve to grip payloads and tools. Each OTCM is also equipped with a retractable motorized socket wrench to attach or detach mechanisms in orbit.

Below the shoulder/torso are the hips, with a "body roll" joint between them. On each hip, and very much like any human handyman, are tool caddies for each arm to reach into, as well as an extendable temporary work platform. Another set of high-resolution TV cameras is installed in this area. Below the hips is another latching mechanism that allows Dextre to be placed on any of a dozen external worksites, including the cart that moves along the station's truss-mounted railway.

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