2.2.1 Manipulators

The payload of Ranger NBV consists of the four manipulators used for telerobotic operations. These are centralized in the manipulator module, which is a 12 inch cubical structure at the front of Ranger to which all four manipulators are mounted. The vehicle configuration was influenced strongly by the previous work conducted in the SSL with BAT and other free flying telerobots.
Although most EVA tasks are designed to be performed using only one arm, two dexterous arms are used by Ranger. Supporting activities such as tool hand-off implicitly require a second manipulator. A second manipulator can also be used to stiffen the dock to the work site when large forces are required.
A rigid grapple to a point near the workspace on the target satellite is desirable. This permits local reaction of work forces back into the satellite structure. Also, limitations in the workspace of the dexterous manipulators require the vehicle to be able to be repositioned with respect to the work site. These requirements lead to the inclusion of a grapple manipulator.
In order to accomplish many of the more complex EVA tasks, a wide range of camera views is necessary. Simple tilt and pan units have proven inadequate for many complicated manipulation tasks. Many researchers have found that wrist mounted cameras are useful for manipulator grasping tasks in which the end-effector is "flown" into position with the assistance of a visual target. SSL experience has shown that for more general tasks a tool-orthogonal view is often preferred. This requirement led to the inclusion of an independent camera manipulator.
A narrow forward-mounted manipulator base enhances versatility. Restricted work volumes are common on existing space systems. Broad shoulders are not desirable in tight quarters. Also, when using multiple dexterous manipulators, overlap of workspaces is required for hand-off and cooperative manipulation.