The two-armed robot (or telemanipulator) Dextre, also known as the Special Purpose Dexterous Manipulator (SPDM), is the latest component of the Mobile Servicing System on the International Space Station (ISS). It is specifically designed to replace some of the activities that would otherwise have required dangerous spacewalks.
Dextre (shown in Fig.1) which is part of Canada's contibution to the International Space Station (ISS) is the 3RD & final stage of the Mobile Servicing System. Dextre works in conjunction with the Canadarm2 which was installed on the ISS in 2001 & the mobile base which was installed in 2002. It is sometimes referred to as the Canada hand by analogy with the Canadarm and Canadarm2.
Figure 1: Dextre the Canadian Space Agency's Special Purpose Dexterous Manipulator
Installation
The Canadian Space Agency's Special Purpose Dexterous Manipulator, aka "Dextre," was successfully launched into orbit on March 11, 2008 aboard the space shuttle Endeavour (mission STS-123). Figure 2 shows Dextre being prepared for launch while Figure 3 shows Dextre all packed up and ready to head off into space aboard the space shuttle Endeavour.
Figure 2: Dextre is being folded up in preparation for launch
Figure 3: Dextre is loaded and ready to go.
Installing Dextre to the ISS required Endeavour astronauts Rick Linnehan and Robert L. Behnken to make three lengthy space walks. Firstly, the astronauts deployed the body section of Dextre on March 14, 2008. Then they connected Dextre to the space station's Canadarm2 (see Fig 4), which supplied the necessary power for Dextre to be “woken up”.
Figure 4: Dextre fully assembled and attached to Canadarm2
Dextre immediately activated the heaters so vital for keeping its joints and electronics warm in the cold environment of space.
One end of Dextre's torso has a special grapple feature that the International Space Station's (ISS) larger Canadarm2 can grasp in order to position Dextre at various work sites around the ISS.
The other end of Dextre's torso has an end effector like that of Canadarm2, which allows Dextre to be stored on the Space Station's special external grapple fixtures or for attachment to the Canadarm2 (Fig.5) to act as a high precision extension to the larger arm.
Figure 5: Graphical depiction of Dextre attached to Canadarm2
This combination of the Canadarm2 and Dextre allows these two robotic systems to reach virtually any site of the ISS desired. It also gives the ISS the ability to perform work upon other vehicles at a greater and safer distance from itself than before.
Bearing in mind that objects in orbit are travelling in excess of 25,000 miles/hour and will cause a lot of damage should they accidentally collide. The additional features, capabilities and added safety that Dextre delivers is essential if we humans are to successfully conquer space.
It was during the second space walk of the mission on March 16, 2008 that astronauts Rick Linnehan and Robert L. Behnken attached Dextre's two 3.35 meters (11 ft) long arms. Then they reattached Dextre to Canadarm2 in order for it to keep warm and allow NASA to conduct a series of thoroughly rigorous tests to ensure that all of Dextre's electronics and moving parts.
After NASA was satisfied, the crew of the Endeavour then conducted further in situ testing of all of Dextre's joints and braking systems. Final outfitting of Dextre the space maintenance robot took place during a third space walk on St Patrick's Day, March 17, 2008.
Design and Delivery
MDA Space Missions designed and built Dextre under contract from the Canadian Space Agency. The Canadian Space Agency bears the ongoing responsibility for its future operations and any training that may be necessary for future space station and ground crews alike. Do not forget that Dextre has the capacity for remote control from earthbound facilities.
With all testing complete Dextre arrived at the Kennedy Space Center in Florida mid-June 2007. There it underwent final flight verification testing and space shuttle integration (packaging and loading) in preparation for launch (Fig.2 and Fig. 3).
Features
Dextre's design plan (see Figure 6) incorporates the following features:
Two identical detachable highly dexterous 3.25 meters (11 ft) arms each of which has 7 joints allowing the following range of movements: Shoulder Roll, Shoulder Yaw, Shoulder Pitch, Elbow Pitch, Wrist Pitch, Wrist Yaw & Wrist Roll
Pivoting Body and Body Roll Joint - The nimble Dextre can pivot at the waist.
Torso mounted lights & video equipment. Dextre's five cameras allow its operators to view its work from practically every angle.
Remote Control via a Power Data Grapple Fixture - Dextre is controllable from a workstation aboard the ISS or by flight controllers on the ground. This is one of its most promoted safety features. In the event of a calamity, earthbound operators are able to conduct procedures via Dextre thereby freeing the ISS crew to attend to more pressing matters.
