The remote manipulator system (RMS) is the shuttle's 'crane', a robot arm fitted in the payload bay of the orbiters to lift objects in and out. The RMS arm is also called the Canadarm, because it was designed and built in Canada (by Spar Aerospace). It first flew on the second shuttle mission, STS-2, in November 1981. It now forms one of the most important features of the shuttle orbiter. The same company are now developing an advanced RMS for remote handling of equipment in the construction, operation and maintenance of space station Freedom. It is known as the mobile servicing system (MSS). The RMS arm measures 15.2 metres long and 38 cm in diameter, and is jointed like a human arm. It is attached to the payload bay at the 'shoulder', has an 'elbow' in the middle, and has a wrist for its 'hand', called the end effector. The end effector is fitted with wires, which wrap around purpose-built grapple fixtures on the payloads handled. Television cameras are mounted on the arm at the elbow and on the end effector. They feed pictures to two TV screens on the right-hand side of the aft crew station at the rear of the orbiter's flight deck. The RMS operator works the RMS arm from a console there, using hand controllers. He or she can view the arm and the payload to be handled on the screens and also through windows that look into the payload bay and upwards through the overhead windows. The RMS arm weighs little more than 400 kg on Earth, yet in space, it can delicately manipulate payloads the size of a bus! It is used routinely for launching satellites, plucking them out of the payload bay and literally placing them in orbit, grasping them by their grapple fixture. It is also used for retrieving satellites from orbit. Some satellites, such as the LDEF (long- duration exposure facility) and Eureca, are designed for periodic deployment and recovery. The RMS has also proved invaluable for recovering satellites not designed to be recovered. This was first done on STS-51A, when two comsats (Westar VI and Palapa B2) were captured and brought back to Earth. On this occasion spacewalking astronauts first attached a 'stinger' to the satellite which carried a grapple fixture that the RMS arm could grip. During such missions the RMS arm provides a mobile platform from which the astronauts can work. The astronauts attach the platform, called a mobile foot restraint or 'cherry picker', to the end of the arm.
