The Space Shuttle Remote Manipulator System (SRMS) and Space Station Remote Manipulator System (SSRMS) have proven the benefit of long-reach manipulators, with the reach of both manipulators in the l5-18-m class. Manipulators with greater reach provide many benefits. The SRMS’s limited reach required an additional 12-m boom to augment its reach during inspection of the belly of the SRMS in support of return to flight following the Columbia disaster.
Berthing operations benefit from longer reach because visiting spacecraft are intercepted at a greater separation, allowing more time to accomplish the berthing maneuver. This additional separation allows capture at higher delta Vs, reduction in the interface forces, and additional time to execute contingency options. If the SSRMS had a longer reach, fewer power data grapple fixtures would be required along the space station truss, and the SSRMS could reach a larger percentage of the space station. Future large space structures, such as large telescopes, space solar power, and fuel depots would benefit from a longerreach manipulator during construction, repair, and upgrade operations.
However, the manipulator architecture of the SRMS and SSRMS does not scale well. Longer manipulators require huge booms and large motors to actuate the joints, driving up weight and reducing packaging efficiency. In addition, the architecture does not lend itself to on-orbit repair, requiring the entire device to be returned to Earth for routine maintenance or repair. Further, the primary flexibility occurs at the joints of these manipulators due to the collocation of the joint drive gear system.
The invention described here addresses the limitation of existing space-based robotic architectures, creating a new class of zero-g manipulators that can be scaled from tens of meters to kilometers, has efficient packaging, higher stiffness, less weight, lower power requirements, and the ability for on-orbit repair.
These manipulators use tension networks to actuate the joints and stiffen the manipulator structure. Both tension actuation of the joints and tension stiffening of the links or booms are novel approaches to space-based manipulators. Each of these approaches enhances the performance of space-based manipulators, and can be used independently or together, depending on mission requirements for reach, packaging efficiency, weight, and dexterity. Tensioning can be accomplished in a variety of ways including through cables, metallic tapes, rigid bar, etc., or some combination of these approaches. Actuating the manipulator joints through tension elements provides large mechanical advantage for the joint motor, enabling use of smaller, lighter-weight motors requiring less power. Low-precision motors can be used because the tension elements can be designed to damp out irregularities in the motor torque, further reducing motor complexity and costs. Single motors can be used per joint, or multiple motors per joint operating in an antagonistic manner, depending on the performance required. In addition, the motors are located away from the mechanical pivot point, simplifying the mechanical design and enabling straightforward on-orbit repair.
The motors can either drive winches where excess material (for example, a cable) is spooled, or capstans where the tension elements circulate, potentially with a tensioning element to accommodate changes in cable length. Further, through the innovative use of tensioned networks, the stiffness of the booms can be increased dramatically, allowing a smaller, lighter-weight system to be realized.