1996-07-01

A Computer Controlled Power Tool for Servicing the Hubble Space Telescope 961531

The Hubble Space Telescope (HST) was designed to be serviced from the shuttle by astronauts performing extravehicular activities (EVA). During the first HST Servicing Mission (STS-61) two types of power tools were flown, the Power Ratchet Tool (PRT) and the HST Power Tool. Each tool had both benefits and drawbacks. An objective for the second HST servicing mission was to combine the reliability, accuracy, and programmability of the PRT with the pistol grip ergonomics and compactness of the HST Power Tool into a new tool called the EVA Pistol Grip Tool (PGT).
The PGT is a self-contained, microprocessor controlled, battery powered, 3/8-inch drive hand-held tool. The PGT may also be used as a non-powered ratchet wrench. Numerous torque, speed, and turn or angle limits can be programmed into the PGT for use during various servicing missions. Batteries Modules are replaceable during ground, Intravehicular Activities (IVA), and EVA operations.
The PGT is grouped into Functional Subsystems and Assembly Modules. The five Functional Subsystems are: Mechanical, Electrical, Battery, Software, and Operator Interfaces. There are five Assembly Modules: Multisetting Torque Limiter, Power Train, Main Housing, Electronics Module, and Battery Module.
The application of satellite mechanism technology and design methods was critical in the production of a compact, ergonomic power tool which meets the accuracy, reliability, and safety requirements for the HST Second Servicing Mission.

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