ISS Canada "hand" (NASA)

The Special Purpose Dexterous Manipulator is a robotic arm or telemanipulator, or "waldo" which is part of the Mobile Servicing System. It is one of the many segments of Canada's contribution to the International Space Station, scheduled to be transported to the station no earlier than 2005. Its creation is managed by the Canadian Space Agency, which will oversee its future operations and the necessary training of station crews.

The Manipulator has been named Dextre, to represent its dexterous nature. It is also known as the Canada hand in contrast to the Canadarm and Canadarm2.

The "Canada hand" term is misleading. While it is true that Dextre is designed to be placed at the end of Canadarm2, it is much bigger and stronger than a human hand, and it is shaped completely differently. It resembles more a headless torso fitted with two extremely agile arms, than any kind of hand. The "torso" pivots at the "waist". The two arms each have seven joints giving a greater freedom of movement than previous systems. At the end of each of these arms a large selection of tools, and other devices can be fitted automatically. The system is called the Orbital Replacement Unit/Tool Changeout Mechanism (OTCM), and it has built-in grasping jaws, retractable socket wrenches and monochrome TV cameras. The lower "torso" of Dextre has a pair of orientable colour TV camera. In addition, it has lights, a tool platfrom and tool holders.

Designed primarily for delicate servicing tasks on the exterior of the space station, it is flexible and strong enough to accomplish many other kinds of tasks in space. It will be typically be used to do such tasks as replacing a 100 kg (220 lb) battery but it could easily insert something as light and small as a videotape cartridge in a VCR.

Dextre has completed its trials in the thermal and vacuum space simulation chambers of the Canadian Space Agency's David Florida Laboratory in Ottawa. It has also been subjected to various electrical and shaking tests in this same facility, to simulate extreme launch conditions.

In early August 2004 NASA declared its intention to use Dextre (or a close copy of it) as the robotic component for the Hubble Space Telescope rescue mission. Technically, NASA intends to have a sole bidder for the construction of the manipulator for the Hubble mission: The robotics division of MacDonald Dettwiler and Associates, which is known as MD robotics. This Canadian engineering firm has already built Dextre for the Canadian Space Agency, and has previous experience in building Canadarm and Canadarm2 and participating in the training of US astronauts and payload specialists in the use of these devices.