Tuesday, April 18, 2001
The International Space Station is being gradually constructed in orbit, with
astronauts and materials supplied by a succession of missions in the Space
But human space walks are risky, so much of the work is done by robotic
cranes. So far, it's all been done by the Little Arm, a 50-ft, 3-inch crane
carried aboard the Shuttle.
On April 19, the Shuttle will bring the station its first permanent crane,
the Canadian-built Canadarm2, also called the Big Arm (www.space.gc.ca/home/index.asp).
Astronauts will do two space walks to attach the 57-ft, 9-inch crane to the
station, and to switch it on (www.shuttlepresskit.com/STS-100/eva14.htm).
Next, a future shuttle flight will bring the arm's "fingers," allowing it to
construct and attach the space station's airlock, scheduled to be delivered on a
shuttle flight in June. In coming years, it will attach the station's solar
wings. It can also catch orbiting satellites, or serve as a mobile work platform
for spacewalking astronauts.
Like the five original Little Arms, the Big Arm was built by MacDonald
Dettwiler Space and Advanced Robotics (MD Robotics, Brampton, Ontario, www.mdrobotics.ca/). Aside from its longer
reach, the billion-dollar Big Arm can do more complex tasks than the Little Arm
since it can "walk" completely around the Space Station, using a "hand" on each
end to move like an inchworm. Although the new arm weighs in at 3,618 lbs, this
motion is possible because its joints have greater freedom of motion than either
the Little Arm or a human arm. It has no trouble supporting its own mass in
zero-gravity space, but since it's designed to lift as much as 255,000 lbs, it
must be made of high-strength aluminum, stainless steel, and graphite epoxy.