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Dextre: Canadian Robotics for the International Space Station

The two-armed Special Purpose Dexterous Manipulator, known as "Dextre," is the third and final component of the Mobile Servicing System (MSS) developed by Canada for the International Space Station. It complements the mobile base and the robotic arm Canadarm2 already installed and operating on the Station.

Versatile Dextre has two arms for delicate servicing tasks on the outside of the
International Space Station

With advanced stabilization and handling capabilities, Dextre can perform delicate tasks that have been reserved for the human touch until now. Delivery of this element increases crew safety, reducing the amount of time that astronauts must spend outside of the Space Station on routine maintenance and freeing time for scientific activities.

Dextre is the world's first on-orbit servicing robot with an operational mission, and it lays the foundation for future satellite servicing and space exploration capabilities.

Design ingenuity and remarkable sensitivity

Like a mechanic in space, Dextre can pivot at the waist, and its shoulders support two identical arms with seven offset joints that allow for great freedom of movement. It is equipped with lights, video equipment, a stowage platform, and four robotic tools. The waist joint allows the operator to change the position of the tools, cameras, and temporary stowage on the lower body with respect to the arms on the upper body.

At the end of each arm is an orbital replacement unit/tool changeout mechanism, or OTCM-parallel jaws that hold a payload or tool with a vice-like grip. For fine manipulation tasks, Dextre has a unique technology: precise sensing of the forces and torque in its grip with automatic compensation to ensure the payload glides smoothly into its mounting fixture.

To grab objects, each OTCM has a retractable motorized socket wrench to turn bolts and mate or detach mechanisms, as well as a camera and lights for close-up viewing. A retractable umbilical connector can provide power, data, and video connection feed-through to payloads.

Dextre can either be attached to the end of Canadarm2 or ride independently on the mobile base system. For several reasons, it is designed to move only one arm at a time: to maintain stability, to harmonize activities with Canadarm on the Shuttle and Canadarm2 on the Space Station, and to minimize the possibility of self-collision.

Strong, with a gentle touch

Dextre can accomplish tasks that require high precision and a gentle touch such as removing and replacing Station components, opening and closing covers, and deploying or retracting mechanisms. Some of the many tasks Dextre will perform include installing and removing small payloads such as batteries, power switching units, and computers, as well as manipulating, installing, and removing scientific experiments.

 

A typical task for Dextre would be to replace a depleted battery (100 kg) and engage all the connectors. This involves bolting and unbolting, as well as millimetre-level positioning accuracy for aligning and inserting the new battery.

Controllable from the ground

As with all elements of the Mobile Servicing System, Dextre can be operated from a workstation aboard the Space Station, or by flight controllers from the ground. Its five cameras, including two pan/tilt cameras below its rotating torso, provide operators with multiple views of the work area.

To prepare for operating any of the Canadian robotic components on the Station, astronauts and cosmonauts undergo rigorous training at the Canadian Space Agency's Operations Engineering Training Facility at the John H. Chapman Space Centre in Longueuil, Quebec.

The Canadian touch on the Space Station

Canada is a partner with the United States, Japan, Russia and 11 European nations in the collaborative project to build an orbiting laboratory. Renowned for its expertise in space robotics, Canada's contribution to the International Space Station is the Mobile Servicing System.

Combining two robotic elements and a mobile platform, the system is designed to work together or independently. The first element is Canadarm2, whose technical name is "Space Station Remote Manipulator System." It was delivered and installed by Canadian Space Agency astronaut Chris Hadfield in 2001. The mobile base system was added to the Station in 2002. Dextre launches aboard Space Shuttle Endeavour on flight STS-123.