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Dextre (Special Purpose Dexterous Manipulator) |
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Launch: Scheduled for 2008
Dextre is an essential tool for maintaining and servicing the space
station. With its dual-arm design providing added flexibility,
Dextre will remove
and replace smaller components on the Station’s exterior, where precise handling is
required. It will be equipped with lights, video equipment, a tool platform and four
tool holders.
Dextre can perform dexterous tasks by sensing various forces and moments on the
payload. In response, it can automatically compensate its movements to ensure the
payload is manipulated smoothly.
With its two arms, Dextre will load and unload objects, use robotic tools, attach
and detach covers and install various units of the Space Station. It will either be
attached to the end of Canadarm2 or ride independently on the Mobile Base System and
have Canadarm2 deliver equipment to it for servicing. It also has four cameras that
will provide the crew inside the Station with additional views of the work areas.
Like Canadarm2 and the Mobile Base System (MBS), the Special Purpose Dexterous Manipulator will be
controlled by the crew inside the International Space Station. This system will allow
the crew to perform many of the tasks that would otherwise require an astronaut to
perform during a demanding spacewalk.
Dextre is a sophisticated dual armed robot, which is part
of Canada's contribution to the International Space Station
(ISS). Along with Canadarm2, whose technical name is the
Space Station Remote Manipulator System, and a moveable work
platform called the Mobile Base System, these three elements
form a robotic system called the Mobile Servicing System
(MSS). The three components have been designed to work
together or independently.
MD Robotics, located in Brampton, Ontario, is the main
contractor of the Dextre. The technology behind Dextre is
built upon the heritage of its predecessor, Canadarm2.
Conceptually the two robots are similar and they both
operate with the support of computers; however, their design
and purpose are different.
Dextre is a complex robot designed to perform intricate
maintenance and servicing tasks on the outside of the ISS.
Dextre will carry out delicate work that, so far, could only
be accomplished by astronauts during spacewalk activities.
In other words, Dextre will provide an alternative to
astronauts, considerably reducing the amount of time that
they have to venture out of the ISS to perform demanding
spacewalks and providing more time for them to perform
science on the ISS.
Upon close inspection of Dextre, one notes its
resemblance to the human shape: an upper body that can pivot
at the waist with shoulders that support two identical arms.
Each arm has a total of seven joints, providing an
incredible amount of freedom when performing a task.
However, Dextre is designed so that only one arm can move at
a time in order to avoid self-collision, achieve greater
stability and maintain operational similarity with
Canadarm2. The greater stability is provided by the immobile
arm, which is first commanded to anchor Dextre to an ISS
stabilization point. At the tip of each arm, we find a
"hand", known technically as the Orbital
Replacement Unit/Tool Changeout Mechanism (OTCM). The OTCM
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 mate and demate
mechanisms on-orbit, as well as lights and a black &
white camera. Dextre lower body is equipped with a pair of
pan/tilt colour cameras that allow astronauts aboard the ISS,
and engineers on the ground, to monitor the task, which is
out of direct eyesight.
A variety of tasks will be performed by Dextre including
installation and removal of small payloads such as
batteries, power supplies and computers; providing power and
data connectivity to payloads; and manipulating, installing,
removing and inspecting scientific payloads. A typical task
for Dextre is to replace a depleted (100 kg) battery, which
involves bolting and unbolting operations as well as
millimetre level positioning accuracy to properly align and
insert the spare battery within its worksite and properly
engage all connectors. This peg-in-the-hole type of task
demands a great amount of precision and a gentle touch to
avoid binding. To achieve this Dextre has a unique feature
which complements its remarkable dexterity: precise sensing
of forces and torques at the "hand" and automatic
compensation to ensure the payload moves smoothly into its
mounting fixture. To illustrate the level of performance of
Dextre, here on Earth it could likely be used to insert an
item as delicate as a videotape into a video recorder.
Dextre is a very versatile robotic tool. It can work
solo, fixed to one of the base points (known as power data
grapple fixtures) along the side of the Station or on the
Mobile Base System. However, most of the time Dextre will do
its work while attached to the free end of Canadarm2 which
will manoeuvre Dextre into position next to the payload
which requires maintenance along the main truss of the ISS.
Astronauts aboard the ISS will operate all of the MSS
components from a robotic workstation. As part of mission
preparation, astronauts must undergo rigorous training to
learn how to operate each component of the MSS. Canadian
Space Agency engineers provide this training at the John H.
Chapman Space Centre in Saint-Hubert, Quebec.
Dextre is currently going through final testing prior to
its launch slated for 2008.
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