JOINTS 

Each subassembly component of the SRMS i.e. the shoulder, elbow or wrist is made up of a basic element called a joint one-degree-of-freedom or JOD.  The JOD's are simply motor driven gearboxes that allow the basic structure of the arm to articulate much like the human arm.  There are two JOD's in the shoulder joint which allow the whole arm to pitch (up and down motion) and yaw (side to side motion).  One in the elbow joint to allow the lower arm to pitch and three in the wrist joint to allow the tip of the arm to pitch, yaw and roll (rotating motion).  SRMS is much more articulate than even the human arm and can therefore accomplish very complex manoeuvres.  The JOD motors are equipped with their own brakes and joint motor speed control.  Each JOD also incorporates a device called an encoder, which accurately measures joint angles.  Thus each joint is capable of moving independently at different speeds and in different directions with respect to any or all the other JOD's.

BOOMS 

Linking the shoulder, elbow and wrist joints are the upper and lower arm booms.  These booms are constructed of graphite-epoxy.  The upper arm boom is approximately 16 ft. long by 13.0 in. in diameter comprising of 16 plies of graphite-epoxy (each ply is .005" thick) for a total weight of just under 50 lbs.  The lower arm boom is approximately 19 ft. long by 13.0 in. in diameter comprising of 11 plies of graphite-epoxy for a total weight of just over 50 lbs.  Each boom is protected with a Kevlar bumper (the same material used in bulletproof vests) to preclude the possibility of dents or scratches on the carbon composite.

WIRING HARNESS 

Just as the arm booms linked the shoulder, elbow and wrist joints mechanically, the wiring harness (electrical cabling) accomplishes the same thing only electrically.  The wiring harness provides electrical power to all the joints and the End Effector (mechanical hand) as well as data and feed back information from each of the joints.  This link continues from the SRMS in the payload bay and continues on into cabin of the space shuttle where astronauts control the actions of the arm remotely. 

END EFFECTOR 

The End Effector or mechanical hand of the SRMS allows the arm to capture stationary or free flying payloads by providing a large capture envelope (a cylinder 8 in. in diameter by 4 in. deep) and a mechanism/structure capable of soft docking and rigidizing.  This action is accomplished by a two stage mechanism in the End Effector which closes three cables (like a snare) around a grapple probe (knobbed pin) bolted onto the payload and then draws it into the device until close contact is established and a load of approximately 1100 lbs. is imparted to the grapple probe.  The forces developed by the End Effector on the payload through the grapple probe will allow for manoeuvring of the payload without separation from the remainder of the SRMS to the positional accuracy’s previously stated. 

CLOSED CIRCUIT TELEVISIONS (CCTV) 

The SRMS has two CCTVs, one at the elbow joint and one at the wrist joint.  The CCTV units are used to aid the astronauts in the positioning of the arm for payload capture/retrieval or payload by capture/deployment. 

SRMS CONTROL SYSTEM 

The space shuttles general-purpose computer (GPC) controls the movement of the SRMS.  The hand controllers used by the astronauts tell the computer what the astronauts would like the arm to do.  Built in software examines what the astronauts commanded inputs are and calculates which joints to move, what direction to move them in, how fast to move them and what angle to move to.  As the computer issues the commands to each of the joints it also looks at what is happening to each joint every 80 milliseconds.  Any changes inputted by the astronauts to the initial trajectory commanded are re-examined and recalculated 
 by the GPC and updated commands are then sent out to each of the joints.  The SRMS control system is continuously monitoring its "health" every 80 milliseconds and should a failure occur the GPC will automatically apply the brakes to all joints and notify the astronaut of a failure condition.  The control system also provides a continuous display of joint rates and speeds, which are displayed on monitors located on the flight deck in the orbiter.  As with any control system, the GPC can be over-rided and the astronaut can operate the joints individually from the flight deck.

THERMAL PROTECTION SYSTEM 

The SRMS is covered over its entire length with a multi-layer insulation thermal blanket system, which provides passive thermal control.  This material consists of alternate layers of godized Kapton, Dacron scrim cloth and a Beta cloth outer covering.  In extreme cold conditions, thermostatically controlled electric heaters (resistance elements) attached to critical mechanical and electronic hardware can be powered on to maintain a stable operating temperature. 

Technical Details

Length	15.2m (50ft.)
Diameter	38cm (15 in.)
Weight on Earth	410Kg (905 lbs.)
Speed of Movement	- unloaded 60 cm/sec. (2 ft./sec.)  - loaded 6 cm/sec. (2.4 in./sec.)
Upper & Lower Arm Boom	Carbon Composite Material
Wrist Joint	Three degrees of movement (pitch +/- 120º, yaw  +/- 120º, roll +/- 447º)
Elbow Joint	One degree of movement (pitch +2º to - 160º)
Shoulder Joint	Two degrees of movement (pitch +145º to -2, yaw +/- 180º)
Translational Hand Controller	Right, up, down forward, and backward movement of the arm
Rotational Hand Controller	Controls the pitch, roll, and yaw of the arm