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Mesoscopic Winch for Precise Extension and Retraction

A cable could be drawn in submicron steps over a range of ≈1 m. A proposed lightweight, micromachined winch would have microscopic structural details and mesoscopic overall dimensions and would be capable of generating bidirectional macro- scopic motion (maximum cable extension or retraction ≈1 m) with submicron increments. Winches like this one could be useful for actuating small mechanisms in scientific instruments and robots: examples of such mechanisms include translation stages; slide shutters and filters for imaging photodetector arrays; pan, tilt, or zoom actuators for cameras; mechanisms for dragging sampling scoops; and steering mechanisms for small robotic vehicles.

Posted in: Machinery & Automation, Briefs, TSP

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Synchronizing Attitudes and Maneuvers of Multiple Spacecraft

A report discusses the problem of controlling the maneuvers of multiple spacecraft flying in formation and, more specifically, making the entire formation rotate about a given axis and synchronizing the rotations of the individual spacecraft with the rotation of the formation. Such formation flying is contemplated for mission in which the spacecraft would serve as platforms for long-baseline-interferometer elements and the synchronized rotations would be needed for slewing of the interferometers. Starting from (1) a particle model of the dynamics of the spacecraft formation, (2) a rigid-body model of the spacecraft-attitude dynamics, and (3) an assumption that one spacecraft would serve as the reference for the positions and orientations of the other spacecraft, the report presents a mathematical derivation of control laws for formation flying in the absence of gravitation and disturbances. A simplified control law suitable for implementation is also derived. Results of a computer simulation for three spacecraft flying in a triangular formation are presented to show that the control laws are effective.

Posted in: Mechanics, Briefs, TSP

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Microfabricated Flow Controllers and Pressure Regulators

Efforts are underway to develop microfabricated flow controllers and pressure regulators that contain as few discrete components as feasible and that are cheaper, more robust, and orders of magnitude smaller than are currently commercially available devices that have similar capabilities. The developmental devices are designed to interact with electronic sensing and control circuits that include microprocessors that, in turn, communicate with host computers of digital feedback control systems. An example of the prototype devices constructed thus far is a hybrid device that includes a flow sensor, a valve containing a TiNi-alloy microribbon shape-memory actuator, and a temperature sensor, with wire-bonded leads for connection to electronic circuits. Windows™-based software for interaction between host computers and the microprocessors associated with these devices has been written. Contemplated further development efforts would be devoted to advancing from the concept of a flow controller on a ceramic substrate to that of a flow controller on an assembly of two or more semiconductor chips. In principle, fabrication on a semiconductor chip could be accomplished without need to assemble discrete components.

Posted in: Mechanics, Briefs

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Formation Alignment of Multiple Autonomous Vehicles

Alignment is achieved by use of lasers, optical sensors, and rule-based controls. A table-top experiment on formation alignment of three air-levitated robotic vehicles has been performed to demonstrate the feasibility of a more general concept of controlling multiple robotic vehicles to make them move in specified positions and orientations with respect to each other. The original intended application of the concept is in the control of multiple spacecraft flying in formation, as described in “Synchronizing Attitudes and Maneuvers of Multiple Spacecraft” (NPO-20569) on page 64 in this issue of NASA Tech Briefs. In principle, the concept could also be applied on Earth to control formation flying of aircraft or to coordinate the motions of multiple robots, land vehicles, or ships.

Posted in: Mechanics, Briefs, TSP

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Ultrasonic/Sonic Vibrating/Rotating Tool Bits

Teeth are made asymmetric to induce rotation without need for rotary actuators. An easy-to-implement design concept shows promise for improving the performances of impact tool bits used in abrading surfaces, drilling, and coring of rock and rocklike materials. The concept is especially applicable to tools actuated with a combination of ultrasonic and sonic vibrations, as in the cases described in “Ultrasonic/Sonic Drill/Corers With Integrated Sensors (NPO- 20856), NASA Tech Briefs, Vol. 25, No. 1 (January 2001), page 38. Such tools were originally intended to be used in scientific drilling and coring of rock; they might also be useful for drilling, coring, and surface grinding of rock for art and construction.

Posted in: Machinery & Automation, Briefs, TSP

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Pulse-Tube Refrigerator for Liquid Hydrogen

An unusually high operating frequency enables reductions of size and weight. An improved closed-loop, two-stage pulse-tube refrigerator provides 4 W of cooling power at a temperature of 15 K. The original intended application of this refrigerator is in preventing boiloff of liquid hydrogen from a propellant tank aboard a spacecraft. The basic refrigerator design can also be adapted to terrestrial applications like cooling superconducting electronic devices.

Posted in: Machinery & Automation, Briefs, TSP

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Fail-Safe, Continue-to-Operate Concept for Jackscrews

Redundant nut increases reliability and facilitates inspections. A fail-safe, continue-to-operate design concept for machine jackscrews calls for the incorporation of a redundant follower nut that would assume the axial jack load upon failure of the primary nut. Heretofore, the way to design for increased reliability of jackscrews has been to provide for multiple jackscrews operating in unison. The present fail-safe, continue-to-operate design concept offers an alternative for preventing catastrophic failures in jackscrews, which are used widely in aeronautical, aerospace, and industrial applications.

Posted in: Machinery & Automation, Briefs

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