<P> The Canadarm is outfitted with an explosive - based mechanism to allow the arm to be jettisoned . This safety system allows the Orbiter's payload bay doors to be closed in the event that the arm fails in an extended position and is not able to be retracted . </P> <P> The Canadarm is 15.2 m (50 ft) long and 38 cm (15 in) diameter with six degrees of freedom . It weighs 410 kg (900 lb) by itself, and 450 kg (990 lb) as part of the total system . The Canadarm has six joints that correspond roughly to the joints of the human arm, with shoulder yaw and pitch joints, an elbow pitch joint, and wrist pitch, yaw, and roll joints . The end effector is the unit at the end of the wrist that grapples the payload's grapple fixture . The two lightweight boom segments are called the upper and lower arms . The upper boom connects the shoulder and elbow joints, and the lower boom connects the elbow and wrist joints . </P> <P> A simulated Canadarm installed on the Space Shuttle Enterprise was seen when the prototype orbiter's payload bay doors were open to test hangar facilities early in the shuttle program . The Canadarm was first tested in orbit in 1981, on Space Shuttle Columbia's STS - 2 mission . Its first operational use was on STS - 3 to deploy and maneuver the Plasma Diagnostics Package . Canadarm has since flown on more than 90 missions with all five orbiters . </P> <P> Since the installation of the Canadarm2 on the International Space Station, the two arms have been used to hand over segments of the station for assembly from the Canadarm to the Canadarm2; the use of both elements in tandem has earned the nickname of' Canadian Handshake' in the media . </P>

On which space shuttle was the canadarm first tested in space