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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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Effect of Gravitation on Noninteracting Trapped Fermions

A report presents a theoretical study of the thermodynamics of an ultralow-temperature gas of fermions that interact with a gravitational field and with an externally imposed trapping potential but not with each other. The gravitational field is taken to define the z axis and the trapping potential to be of the form (m/2) (ωxx2+ωyy2+ωzz2), where m is the mass of a fermion; x, y, and z are Cartesian coordinates originating at the center of the trap; and the ω values denote effective harmonic- oscillator angular frequencies with respect to motion along the respective coordinate axes. The single-particle energy is found from the solution of the time-dependent Schroedinger equation for a Hamiltonian that includes kinetic energy plus the gravitational and trapping potentials. The equation for the single-particle energy is combined with Fermi statistics to obtain equations for the chemical potential, internal energy, and specific heat of the gas; the number of trapped fermions; and the spatial distribution of fermions at zero temperature. The equations reveal the ways in which the Fermi energy, the specific heat, and the shape of the Fermion cloud are affected by the gravitational field and the anisotropy of the trapping field.

Posted in: Briefs, TSP

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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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Algorithms for Collision Avoidant Formation Flying

A report discusses algorithms for realtime planning of translation paths of multiple spacecraft flying in formation. The algorithm takes account of requirements to avoid collisions while operating within resource constraints (e.g., not calling for an acceleration greater than maximum possible) and striving for optimality (e.g., completing a change of formation in minimum time or at minimum energy cost). The optimality/collision- avoidance problem is formulated as a parameter-optimization problem, in which the translation path of each spacecraft is parameterized by polynomial functions of time. It is shown that this parameterization is the key to the solution of the parameter-optimization problem in that it enables decoupling of the collision-avoidance and accelerationlimit constraints, thereby making it possible to solve the problem in two stages. In the first stage, one constructs feasible paths that satisfy only the collision-avoidance constraints subject to certain optimality criteria. It is shown that the acceleration- limit constraints can be imposed a posteriori to compute the required maneuver duration such that at least one acceleration component is saturated. This also enables construction of paths that require minimum time in the class of solutions being considered.

Posted in: Mechanics, Briefs, TSP

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Quantum Mechanics of Harmonic Oscillator in External Fields

A report presents a theoretical study of a harmonic oscillator in homogeneous or nonhomogeneous externally applied electric and/or gravitational fields. The standard quantum-mechanical formalism for a simple harmonic oscillator, starting with the Hamiltonian and the associated creation and annihilation operators, is modified to incorporate the additional terms representing the external fields. The correspondingly modified solutions of the Schroedinger equation are derived.

Posted in: Briefs, TSP

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Portable Instrument Detects Very Dilute Airborne Organics

This instrument offers an attractive alternative to GC/MS. A small, lightweight, low-power instrument, denoted a proton-transferreaction/ ion-mobility spectrometer (PTR-IMS) has been developed for detecting airborne organic compounds at concentrations in the sub-parts-per-billion range. Instruments like this one could be used on distant planets (such as Mars) to search for trace organic compounds indicative of life as well as numerous potential terrestrial uses: A few examples include medical applications (e.g., analyzing human breath to detect compounds associated with certain deadly diseases such as lung cancer and cirrhosis of the liver), lawenforcement applications (detecting airborne traces of explosives and drugs), environmental monitoring (detecting airborne pollutants and toxins), and military applications (detecting chemical warfare agents).

Posted in: Briefs, TSP

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Solar Simulator for a Portable Solar-Absorptance Instrument

The principal advantages are portability and accurate normalized AM0 spectrum. A special-purpose solar simulator includes (1) a tungsten lamp that serves as a gray-body radiator with a temperature of 3,200 K and (2) a mosaic of filters such that the filtered lamp output has the same normalized spectral irradiance as that of sunlight outside the atmosphere of the Earth. This solar simulator is intended for use as the illuminator in a portable instrument that measures solar absorptances and total emittances of samples of materials.

Posted in: Briefs

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