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Center Innovation Fund: MSFC CIF

Flexible Electrostatic Tools for Capture & Handling, Year 2 (FETCH)

Completed Technology Project

Project Description

Conceptual Design of FETCH Gripper

Fundamental to many of NASA’s in-space transportation missions is the capture and handling of various objects and vehicles in various orbits for servicing, debris disposal, sample retrieval and assembly without the benefit of sufficient grapple fixtures and docking ports. To perform similar material handling tasks on earth, pincher grippers, suction grippers or magnetic chucks are used, but are unable to reliably grip aluminum and composite spacecraft, Insulation, radiators, solar arrays, or extra-terrestrial objects in the vacuum of outer space without dedicated handles in the right places. The electronic Flexible Electrostatic Technologies for space Capture & Handling (FETCH) will enable reliable and compliant gripping (soft dock) of practically any object in various orbits or surfaces without dedicated mechanical features, very low impact capture, and built-in proximity sensing without any conventional actuators. Originally developed to handle semiconductor and glass wafers during vacuum chamber processing without contamination, the normal rigid wafer handling chucks are replaced with thin metal foil segments laminated in flexible insulation driven by COTS solid state high voltage power supplies. The flexible electrostatic gripper pads can be adapted to various space applications with different sizes, shapes, and foil electrode layouts even with openings through the gripper pads for addition of guidance sensors or injection of permanent adhesives. With gripping forces estimated between 0.5 and 2.5 pounds per square inch or 70-300 lb./sq. ft. of surface contact, the FETCH can turn-on and turn-off rapidly and repeatedly to enable sample handling, soft docking, in-space assembly, precision relocation, and surface translation for accurate anchoring. This effort will test the proximity sensing and gripping force of the first generation FETCH gripper pads in an instrumented vacuum test chamber with assorted sample materials, shapes, support structures, and grip angles. Additional testing will demonstrate capture/soft docking and handling of different sizes, masses, and configurations beyond a stationary nano-sat mock-up on MSFC’s Flat Floor. The FETCH grippers utilize phased high voltages on the gripper electrodes to induce attractive electro-static charges in the surface of the object being handled whether it is metal, composite, MLI, glass, or even rock. Current docking and orbital debris capture requires pincher type grippers or probe/spears to grab protrusions or insert into cavities or penetrate objects. This requires some cooperative target design features and precision alignment to engage. . Harpoons create additional debris, explosive venting, and many other hazardous conditions. Most old satellites, derelict upper stages and asteroids don’t have handles in the proper places for orbital relocation. Rigid electro-static grippers have been used for years in semi-conductor manufacturing and other vacuum chamber processing with capacitive proximity sensing, very low impact capture & release, no residual contamination, and without motors. We have demonstrated that A flexible electro-static or electro-adhesion gripper that is all electric and can conform and capture various shapes, sizes, and materials without target preparations, generates pull-in force across the gap to grip and self-align (similar to magnetics), and releases cleanly without active motors in space. We have demonstrated that the ES grippers’ primary holding strength is parallel to the gripping surface and the support mechanism must apply the handling force while minimizing “peeling” motions. Flexible electro-static Gripper pads with the correct size, shape, and configuration of attach points, compliance mechanisms, and electrodes can successful conform to various object shapes. Additional pad shapes, electrode patterns and openings (for sensors or permanent adhesive injection) can be designed that will sense and grip with standard programmable electro-static power supplies. By using two or more ES grippers arranged like an octopus’s tentacles on a retractable boom or ES grippers on multiple booms, a very large object or tank can be gripped and safely pulled in for berthing or assembly without docking thrusters that create large residual collision or water-hammer forces. Spacecraft separation is done with boom extension and ES switching. “Boom docking” was the second choice behind the drogue and probe mechanism chosen for the Apollo docking mechanism and the Russian docking mechanism, but the Japanese and both US Commercial cargo ships use berthing from a stationary station-keeping point. ES gripper pads can be used as feet or shoes to allow robots, landers, and rovers to transverse various surfaces and angles with gripping force proportional to the induced ES force in low and micro-gravity such as an inspection robot walking on the outside of a spacecraft with propulsion, rails, or contamination or a lander or rover on an asteroid or the steep side of a crater without the fear of falling over or floating off without using penetrating anchors or tethers or hunting for crevices for grippers. (Gravity boots)

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