Upgraded space robot will lend a hand

All the things that Dextre can do
Dextre is designed to relieve astronauts of many of the tasks that now require arduous, time-consuming and hazardous spacewalks. The exact portion of astronaut labor that Dextre can perform is hard to judge in advance, but NASA experts believe it’s between a quarter and half. This includes standard services such as battery replacement, attaching or detaching instrument covers, plugging or unplugging cables, emplacement and retrieval of exposure samples, adjustment of thermal and debris impact shielding, and inspection of the exterior for damage.

Items that need to be sent out from inside the station, or brought back in, can pass through a garbage-can-sized airlock on the Japanese science lab, which is within Dextre’s grasp when mounted on the end of the manipulator arm. That lab will also be installed in a few months.

Dextre's operational value goes beyond mere workload relief. Because spacewalks take so long to prepare and have such a high overhead, minor inspection and maintenance tasks are strung together for each walk — but they may have to wait months before enough work has piled up to justify the activity. The robot arm and its new appendage could be moved into position for a desired task in a matter of days from the time the activity was approved.

Dextre can also be parked atop the station’s mobile work platform, using the grapple fixture at its base. While in that position, the big arm could bring Dextre objects that require robotic handwork, and could hold the objects while Dextre worked on them. In practice, Dextre will grab the object it’s working on with one hand and manipulate with the other — the arms are operated alternately to keep simultaneous motion from leading to a collision.

Fixing the robot
During the years that Dextre will be in space, it will need preventive maintenance as well as breakdown servicing. One arm can detach the other, if needed, and pass it into the larger Quest airlock normally used for astronauts. There it can be repaired with the best manipulators in orbit: human fingers.

At other times, spacewalking astronauts and Dextre will operate side by side, with the robot passing tools and hardware as needed, and helping push the "cheater bar" when more force is required on a sticky nut. The design will evolve through experience, and new specialized tools can be sent up in the future to load into Dextre’s tool caddies.

In a massive system as complex as the space station, unexpected and unpredictable needs are sure to arise that could be addressed by Dextre's close examination, manipulative dexterity and sometimes a hard smack. The most important accomplishments of Dextre are inherently hard to predict in advance. But I will make one prediction: Someday, NASA will look back and be glad it brought Dextre on board.

A shorter version of this report appeared in Robot magazine.

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