Mechanical & Fluid Systems

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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Instrumented Bolt Measures Bending Moments Within Itself

The direction as well as the magnitude of bending can be determined. The Ultrabend bolt is a specially designed bolt instrumented with strain gauges (see figure) that are connected into twin Wheatstone-bridge circuits. The geometric arrangement of the strain gauges is such that by suitable electrical switching of the Wheatstone-bridge circuits, these circuits can be made to either (1) suppress responses to bending and torsional stresses while putting out signals indicative of axial preload or (2) suppress responses to axial and torsional stresses while putting out signals indicative of the magnitude and direction of the bending moment in the bolt. Switching between these two measurement modes is accomplished by use of field-effect transistors controlled by a logic circuit.

Posted in: Mechanics, Briefs

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Improved Piezoelectrically Actuated Microvalve

The improvements are intended to ensure less leakage and true normally-closed operation. Figure 1. The Previous Version of the Valve, like the present version, was opened by applying a voltage that caused the piezoelectric actuator to contract slightly.Efforts are underway to implement an improved design of the device described in “Normally Closed, Piezoelectrically Actuated Microvalve” (NPO-20782), NASA Tech Briefs, Vol. 25, No. 1 (January 2001), page 39. To recapitulate: This valve is being developed as a prototype of valves in microfluidic systems and other microelectromechanical systems (MEMS). The version of the valve reported in the cited previous article (see Figure 1) included a base (which contained a seat, an inlet, and an outlet), a diaphragm, and an actuator. With the exception of the actuator, the parts were micromachined from silicon. The actuator consisted of a stack of piezoelectric disks in a rigid housing. To make the diaphragm apply a large sealing force on the inlet and outlet, the piezoelectric stack was compressed into a slightly contracted condition during assembly of the valve. Application of a voltage across the stack caused the stack to contract into an even more compressed condition, lifting the diaphragm away from the seat, thereby creating a narrow channel between the inlet and outlet.

Posted in: Mechanics, Briefs, TSP

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