Mechanical & Fluid Systems

Integrated Colloid Thrusters for Microspacecraft

A report proposes the development of a microfabricated, integrated colloid thruster as a prototype of devices for propulsion and control of the attitudes of microspacecraft. (In a colloid thruster, a beam of positively charged, microscopic droplets is extracted electrohydrodynamically from a column of liquid and accelerated electrostatically to produce thrust.) Unlike other electrical thrusters, colloid thrusters are amenable to extreme miniaturization. The direction of thrust would be controlled electronically through selective activation of accelerator electrodes, eliminating the need for mechanical gimbals.

Posted in: Mechanics, Briefs, TSP

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Improvements in a Piezoelectrically Actuated Microvalve

A report discusses the continuing development of a normally closed, piezoelectrically actuated valve fabricated mostly by micromachining of silicon. The design and operation of the microvalve as described in the instant report are basically the same as those of the version described in “Improved Piezoelectrically Actuated Microvalve” (NPO-30158), NASA Tech Briefs, Vol. 26, No. 1 (January 2002), page 29. Major elements of design described in both the instant report and the cited prior article include (1) a pressure-aided sealing configuration that contributes to the desired normally-closed mode of operation and (2) knife-edge sealing rings that reduce susceptibility to trapping of particles and the consequent leakage. The report also presents additional information concerning details of design and fabrication, including, notably, additional justification for knife-edge (in contradistinction to blunt-cross-section) sealing rings: The knife-edge sealing rings provide greater sealing pressure at a given sealing force, thereby reducing the leak rate and even making it possible to achieve an adequate seal with a hard seat. A potential additional advantage of the knife-edge/hard-seat design is that contact pressures may be high enough to crush contaminant particles, thereby reducing the leakage attributable to contaminants.

Posted in: Mechanics, Briefs, TSP

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Low-Energy Transfer From Near-Earth to Near-Moon Orbit

A report presents a theoretical approach to designing a low-energy transfer of a spacecraft from an orbit around the Earth to ballistic capture into an orbit around the Moon. The approach is based partly on the one presented in “Low-Energy Interplanetary Transfers Using Lagrangian Points” (NPO-20377), NASA Tech Briefs, Vol. 23, No. 11 (November 1999), page 22. The approach involves consideration of the stable and unstable manifolds of the periodic orbits around the Lagrangian points L1 and L2 of the Sun/Earth and Earth/Moon systems. (The Lagrangian points are five points, located in the orbital plane of two massive bodies, where a much less massive body can remain in equilibrium relative to the massive bodies.)

Posted in: Mechanics, Briefs, TSP

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Software for Designing Actively Controlled Structures

One program offers capabilities heretofore available only in separate programs. SMARTCOM is a computer program for the analysis and design of actively controlled “smart” structures. Typically, an actively controlled “smart” structure incorporates piezoelectric sensors and actuators that are used, in conjunction with an electrical control system, to damp vibrations. As is the case for other structures, the analysis and design of actively controlled “smart” structures is often best accomplished with the help of finite-element computer programs. Unfortunately, prior finite-element codes do not offer coupled analyses of the mechanical, electrical, and thermal properties of “smart”-structure materials. Also, they are not directly linked with control software, making it necessary to use separate finite-element and control programs to analyze controlled structures. Furthermore, the programs used heretofore to design “smart” structures do not offer capabilities for optimization or for probabilistic or fuzzy analysis.

Posted in: Mechanics, Briefs, TSP

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Magnetically Moved Trim Masses for Fine Position Control

Control would be achieved without spurious effects generated by propulsion systems. Systems of caged trim masses manipulated by magnetic fields have been proposed for effecting fine control of the positions and/or orientations of spacecraft. The systems were conceived for use during observations by spaceborne interferometers, the component instruments of which (1) are located on multiple spacecraft flying in formation and (2) are required to be kept aligned with each other within narrow position and orientation tolerances. The proposed systems would make it possible to avoid the spurious effects generated by the spacecraft propulsion systems that would otherwise have to be used for fine position control; the spurious effects would include vibrations, exhaust, and flashes of light, which would be detrimental to the interferometric observations. Terrestrial versions of the proposed systems might be useful for fine horizontal positioning of delicate scientific instruments.

Posted in: Mechanics, Briefs, TSP

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Motor Drive for Multiple Horizontally Rotating Bioreactors

Bioreactors can be installed and removed easily. The figure depicts a mechanism that is capable of simultaneously rotating as many as six disposable bioreactor chambers about horizontal axes. The particular bioreactor chambers for which this mechanism is designed are high-aspect-ratio vessels (HARVs), which are round cylindrical vessels developed by NASA.

Posted in: Briefs

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Tip Fences for Reduction of Lift- Generated Airframe Noise

These simple, easily retrofitted devices reduce drag as well as noise. Tip fences have been invented to reduce the noise generated in the airflows about the high-lift systems (the flaps and slats) of airplane wings. Tip fences also afford an important secondary benefit by increasing lift-todrag ratios.

Posted in: Briefs, TSP

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