Structures and Mechanisms
Section 4.3.7.
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Remote Manipulator System

For the Low Earth Orbit Assembly Node, a Remote Manipulator System will be required for assembly of the moonship stack. This RMS will very likely be a copy of the International Space Station's arm.

For the International Space Station's arm, the contractor SPAR Aerospace has made some dramatic departures from the Shuttle arm. Among the changes is the ability of the arm to inch-worm from one Power-Data Grapple Fixture (PDGF) to another.

They've also changed the joints so that they are offset opposing motors. The ISS Remote Manipulator System (RMS) has seven segments. The three outboard segments on each side are mirror images of each other, with an end effector plus power and data connectors on each end.

If either end effector is affixed to a PDGF, the other end can operate as a manipulator. If the free end grabs a PDGF (as opposed to a plain grapple fixture) on the object it is manipulating, it can provide power and data to the object.

Concept Sketch of ISS Remote Manipulator System

This image has some more notes. The boom lengths are arbitrary; they were drawn short to fit the RMS into the box. The booms are about 6 inches in diameter, and the end effectors are about 9 inches in diameter.

Note that the outer part of each end effector can rotate. So you can think of the end affector, attached to a PDGF, as a yaw unit, and the multiple joints of the main RMS booms as the pitch unit. There's a roll joint at each end effector that can rotate in a plane 90 degrees from the main arm joints, allow the RMS to position its free end effector in any point in space within its reach, and in any orientation.

You can add as many booms as you want, the seven segments should be enough to do just about anything. Offset each boom in a stack so that each motor can rotate a full 360 degrees. That gets us away from the joint singularities which plague the Shuttle RMS.

Structures and Mechanisms

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