elbow of the ERA, and composes three main components; the Application Layer (AL), the Service Layer (SL), and the operating system (OS). The application layer contains the high level command, mission plan, and event handling; the service layer contains the main robot motion control loops, motion related checks and image processing; together the AL and SL constitute the Application software (ASW). Together the OS and ASW provide the main control the arm. Located with in the ECC's RISC subsystem is the ERA's main central processing unit (CPU). The main CPU is a Temic designed ERC32 with 10 MHz clock, addressing 1.5 megabytes (Mb) of memory, as well as 32 kilobytes (Kb) of ROM. The ECC's I/O subsystem includes an Intel 80C186 with 11 MHz clock addressing 16 kB ROM. It handles the communications between the RISC processor and the other subsystems of the ERA. The ECC's housekeeping subsystem includes an Intel 80C31 with 8 kB ROM. Joint subsystem Located in each wrist and in the elbow, there is one microprocessor that takes care of the bus communication, local inhibits, and safety checks, as well as general housekeeping. The communications of the Joint subsystem are handled by the Joint I/O which included an Intel 80C31 with 8 MHz clock, and 24kB of ROM, as well as communication through dual ported RAM. The control of the subsystem was handled by an Intel 80C32 with 27 MHz clock, addressing 16 kB ROM and 8 kB DPRAM. The possessor ran high speed digital control loops. End effector subsystem While the ECC handles primary control of the end effectors, the EES still includes its own micro-processor to aid in control. Using a torque/force sensor inside the end effectors, the ECC actively controls the arm's pose to keep the contact forces within tight limits. To handle the drift and calibration, the torque force sensor pre-processes the data locally, with its own microprocessor. The processor located within the sensor is an Intel 80C86 with 7.2 MHz clock, addressing 64kB of memory and 32 kB ROM. A separate processor in the end effector control electronics takes care of the bus communication, grapple mechanism control, and general housekeeping. The processor also controls the Integrated Service Tool. The processor is Intel 80C31 with 12 MHz clock, addressing 32 kB RAM and 48 kB ROM. Control Astronauts can control the ERA from both inside and outside the space station. The ERA