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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Silicon Membrane Mirrors with Electrostatic Shape Actuators

Efforts are under way to develop deformable mirrors equipped with microscopic electrostatic actuators that would be used to maintain their reflective surfaces in precise shapes required for their intended applications. Unlike actuators that depend on properties of materials (e.g., piezoelectric and electrostrictive actuators), electrostatic actuators are effective over a wide temperature range. A mirror of the present type would be denoted a MEMSDM (for microelectromechanical system deformable mirror). The reflective surface of such a mirror would be formed on a single-crystal silicon membrane that would be attached by posts to a silicon actuator membrane that would, in turn, be attached by posts to a rigid silicon base (see figure). The actuator membrane would serve as the upper electrode of a capacitor. Multiple lower electrodes, each occupying a conveniently small fraction of the total area, would be formed on an electrically insulating oxide layer on the base, thereby defining a multiplicity of actuator pixels. The actuator membrane would be corrugated in a pattern that would impart mechanical compliance needed for relaxation of operational and fabrication-induced stresses and to minimize the degree of nonlinearity of deformations. The compliance afforded by the corrugations would also help to minimize the undesired coupling of deformations between adjacent pixels (a practical goal being to keep the influence coefficient between adjacent pixels below 10 percent).

Yang, Eui-Hyeok↗
NASA NTRS2006

Thermal Challenge for Sun-Viewing Instruments on Solar Probe 3 R(sub s) from Sun

The Solar Probe science team at NASA GSFC is considering enhance science observations by adding the nadir viewing Plasma Spectrometer instrument and using heat shields to protect the Plasma Wave antennas to permit full extension at 3 R. The electrostatic mirror of the Plasma Spectrometer is thermally protected from the Sun by a miniature sunshield that consists of two carbon-carbon composite layers, and a much smaller carbon-carbon heat shield. The sun-viewing surface of the miniature sunshield has an Al2O3 thin film coating. The slope of the sunshield is minimized to the smallest possible extent so that it can still accommodate the elliptical electrostatic mirror. Two small MLI flaps minimize the heat radiation from the Plasma Spectrometer to the spacecraft bus. This design meets the thermal requirements. Each of the four Plasma Wave wire antennas is 5 m long, and thermally protected from the Sun by a sunshield. The sunshield consists of two carbon-carbon composite sheets. One sheet views the Sun, and one does not. The slope of most of the sun-viewing sheet is 23deg with the nadir axis. For mechanical reason, it gradually increases to 37.5deg at the tip. The exterior of the sun viewing surfaces has a thin film of Al2O3. The exterior of the shaded sheets has a thin film of vapor deposited rhodium. It minimizes the heat radiation to the spacecraft bus. A high temperature MLI blanket between the carbon-carbon sheets radiatively isolates them. The thermal design meets the temperature requirements, but exceeds the 20 W limit of heat radiation to the spacecraft bus by 20 W. Thermal options to reduce the heat radiation include reducing the alpha to epsilon ratio of the Al2O3 thin film and reducing the number of antennas to three. Testing in 2006 includes thermal model validation and materials testing. High temperature ovens and a high light intensity Vortex Lamp will be used.

Choi, Michael K.↗
NASA NTRS1996

Computation of Static Shapes and Voltages for Micromachined Deformable Mirrors with Nonlinear Electrostatic Actuators

In modeling micromachined deformable mirrors with electrostatic actuators whose gap spacings are of the same order of magnitude as those of the surface deformations, it is necessary to use nonlinear models for the actuators. In this paper, we consider micromachined deformable mirrors modeled by a membrane or plate equation with nonlinear electrostatic actuator characteristics. Numerical methods for computing the mirror deformation due to given actuator voltages and the actuator voltages required for producing the desired deformations at the actuator locations are presented. The application of the proposed methods to circular deformable mirrors whose surfaces are modeled by elastic membranes is discussed in detail. Numerical results are obtained for a typical circular micromachined mirror with electrostatic actuators.

Wang, P. K. C.↗
DOE OSTI2012

Electron caustic lithography

A maskless method of electron beam lithography is described which uses the reflection of an electron beam from an electrostatic mirror to produce caustics in the demagnified image projected onto a resist-coated wafer. By varying the electron optics, e.g. via objective lens defocus, both the morphology and dimensions of the caustic features may be controlled, producing a range of bright and tightly focused projected features. The method is illustrated for line and fold caustics and is complementary to other methods of reflective electron beam lithography.

43 PARTICLE ACCELERATORS↗
NASA NTRS1992

Negative-ion formation in the explosives RDX, PETN, and TNT using the Reversal Electron Attachment Detection (READ) technique

In the search for high sensitivity and direct atmospheric sampling of trace species, techniques have been developed such as atmospheric-sampling, glow-discharge ionization (ASGDI), corona discharge, atmospheric pressure ionization (API), electron-capture detection (ECD), and negative-ion chemical ionization (NICI) that are capable of detecting parts-per-billion to parts-per-trillion concentrations of trace species. These techniques are based on positive- or negative-ion formation via charge-transfer to the target, or electron capture under multiple-collision conditions in a Maxwellian distribution of electron energies at the source temperature. One drawback of the high-pressure, corona- or glow-discharge devices is that they are susceptible to interferences either through indistinguishable product masses, or through undesired ion-molecule reactions. The ASGDI technique is relatively immune from such interferences, since at target concentrations of less than 1 ppm the majority of negative ions arises via electron capture rather than through ion-molecule chemistry. A drawback of the conventional ECD, and possibly of the ASGDI, is that they exhibit vanishingly small densities of electrons with energies in the range 0-10 millielectron volts (meV), as can be seen from a typical Maxwellian electron energy distribution function at T = 300 K. Slowing the electrons to these subthermal (less than 10 meV) energies is crucial, since the cross section for attachment of several large classes of molecules is known to increase to values larger than 10(exp -12) sq cm at near-zero electron energies. In the limit of zero energy these cross sections are predicted to diverge as epsilon(exp -1/2), where epsilon is the electron energy. In order to provide a better 'match' between the electron energy distribution function and attachment cross section, a new concept of attachment in an electrostatic mirror was developed. In this scheme, electrons are brought to a momentary halt by reversing their direction with electrostatic fields. At this turning point the electrons have zero or near-zero energy. A beam of target molecules is introduced, and the resultant negative ions extracted. This basic idea has been recently improved to allow for better reversal geometry, higher electron currents, lower backgrounds, and increased negative-ion extraction efficiency. We present herein application of the so-called reversal electron attachment detector (READ) to the study of negative-ion formation in the explosives molecules RDX, PETN, and TNT under single-collision conditions.

Chutijian, Ara↗
DOE OSTI2014

Development of position-sensitive time-of-flight spectrometer for fission fragment research

A position-sensitive, high-resolution time-of-flight detector for fission fragments has been developed. The SPectrometer for Ion DEtermination in fission Research (SPIDER) is a 2E–2v spectrometer designed to measure the mass of light fission fragments to a single mass unit. The time pick-off detector pairs to be used in SPIDER have been tested with α-particles from 229Th and its decay chain and α-particles and spontaneous fission fragments from 252Cf. Each detector module is comprised of thin electron conversion foil, electrostatic mirror, microchannel plates, and delay-line anodes. Particle trajectories on the order of 700 mm are determined accurately to within 0.7 mm. Flight times were measured with 250 ps resolution FWHM. Computed particle velocities are accurate to within 0.06 mm/ns corresponding to a precision of 0.5%. As a result, an ionization chamber capable of 400 keV energy resolution coupled with the velocity measurements described here will pave the way for modestly efficient measurements of light fission fragments with unit mass resolution.

2E-2v↗
NASA NTRS1987

Generation of intense negative ion beams

An electron gun is used with a mirror electrostatic field to produce zero or near zero velocity electrons by forming a turning point in their trajectories. A gas capable of attaching zero or near zero velocity is introduced at this turning point, and negative ions are produced by the attachment or dissociative attachment process. Operation may be continuous or pulsed. Ions thus formed are extracted by a simple lens system and suitable biasing of grids.

Chutjian, Ara↗
NASA NTRS1989

Pulsed, high-current, in-line reversal electron attachment detector

A new, pulsed, high-current, in-line reversal electron attachment ionizer/detector is described. The ionizer is capable of delivering a beam of electrons into an electrostatic mirror field to form a planar wall of electrons having zero kinetic energy. Electron attachment to a molecular target at the reversal point produces either parent or fragment negative ions through a zero-energy (s-wave) state. The atomic or molecular ion is pulsed out of the attachment region approximately 2 microsec after the electrons are pulsed off, and focused onto the entrance plane of a quadrupole mass analyzer. The sensitivity of the apparatus is preliminarily assessed, and its higher-energy behavior with regard to molecular attachment and ionization is described.

Bernius, Mark T.↗
NASA NTRS1992

Increased response of the reversal electron attachment detector and modeling of ion space-charge effects

Design and sensitivity tests of a modified version of the so-called reversal electron attachment detector (READ) are presented. The new version uses a spherical cathode capable of emitting higher electron currents. As in the original READ (which used a planar emitter) electrons are focused into an electrostatic mirror which reverses their trajectories. In the reversal region electrons have essentially zero energy and attach to target molecules to form negative ions. The electron gun lens system has been modified using a field and trajectory code with space charge included. Electron trajectories have been calculated for 1-mA current focused into a reversal region of 3.5-mm diameter. The detection limit of the apparatus is approximately 25 times lower than for the original READ. Nonlinearity in the measured signal vs electron current is described by a model in which a spherical ball of ions expands outward with velocity determined by the space-charge force and the initial velocity of ion formation.

Boumsellek, S.↗
NASA NTRS2003

Genesis Discovery Mission: Science Canister Processing at JSC

Genesis addresses questions about materials and processes involved in the origins of the solar system by providing precise knowledge of solar isotopic and elemental compositions. Solar wind ions are collected and returned to Earth for analyses. The spacecraft has two primary instruments to collect solar wind: a set of collector arrays each of which can deploy to sample different solar wind regimes, and a concentrator that is an electrostatic mirror to concentrate and focus low mass ions onto a 6 cm target. One of the key challenges to obtaining a good sample of solar wind, uncontaminated by terrestrial atoms, is to have clean collection surfaces in a clean sample canister and clean facilities to handle the samples for allocation and future reference. The Johnson Space Center (JSC) is responsible for contamination control for the mission, for ensuring the cleanliness of collection surfaces, and for providing a clean environment for handling of the samples. The level of cleanliness required is high; at the time of analysis (after sample return), the surface contamination by C, N, O must each be <10(exp 15) atoms/sq cm and for other elements the number of atoms/sq cm of each surface contaminant shall not exceed the estimated solar wind fluence of the species (varies by element between U at approx. 10(exp 4) atoms/sq cm to Fe, Si, Mg, and Ne at approx. 10(exp 12) atoms/sq cm).

Stansbery, E. K.↗
NASA NTRS2003

Genesis Solar-Wind Sample Return Mission: The Materials

The Genesis spacecraft has two primary instruments which passively collect solar wind. The first is the collector arrays , a set of panels, each of which can deploy separately to sample the different kinds of solar wind (regimes). The second is the concentrator, an electrostatic mirror which will concentrate ions of mass 4 through mass 25 by about a factor of 20 by focusing them onto a 6 cm diameter target. When not deployed, these instruments fit into a compact canister. After a two year exposure time, the deployed instruments can be folded up, sealed into the canister, and returned to earth for laboratory analysis. Both the collector arrays and the concentrator will contain suites of ultra-high purity target materials, each of which is tailored to enable the analysis of a different family of elements. This abstract is meant to give a brief overview of the Genesis mission, insight into what materials were chosen for flight and why, as well as head s up information as to what will be available to planetary scientist for analysis when the solar-wind samples return to Earth in 2003. Earth. The elemental and isotopic abundances of the solar wind will be analyzed in state-of-the-art laboratories, and a portion of the sample will be archived for the use of future generations of planetary scientists. Technical information about the mission can be found at www.gps.caltech.edu/genesis.

Jurewicz, A. J. G.↗
NASA NTRS2005

Genesis Recovery Processing

The Genesis spacecraft, launched in August 2001 to collect samples of the solar wind, returned to Earth on 8 September 2004. The Sample Return Capsule (SRC) failed to deploy its drogue parachute and parafoil and subsequently impacted the Utah Test and Training Range (UTTR) at an estimated 310 kph (193 mph). The goal of the Genesis mission to collect and return samples of the solar wind for precise elemental and isotopic analysis provides the scientific community with a unique set of materials to aid in understanding the origin of our solar system. The spacecraft orbited the Earth-Sun L1 point for 29 months exposing a suite of fifteen types of ultrapure, ultraclean materials in several different locations. Most of the materials were mounted on fixed or deployable wafer panels called collector arrays . A few materials were mounted as targets in the focal spot of an electrostatic mirror (the concentrator ). Other materials were strategically placed to maximize the area for solar-wind collection.

Stansbery, E. K.↗
NASA NTRS2008

Chemical sensor system

A chemical sensing apparatus and method for the detection of sub parts-per-trillion concentrations of molecules in a sample by optimizing electron utilization in the formation of negative ions is provided. A variety of media may be sampled including air, seawater, dry sediment, or undersea sediment. An electrostatic mirror is used to reduce the kinetic energy of an electron beam to zero or near-zero kinetic energy.

Darrach, Murray R.↗
NASA NTRS2002

The Genesis Mission: Contamination Control and Curation

The Genesis mission, launched in August 2001, is collecting samples of the solar wind and will return to Earth in 2004. Genesis can be viewed as the most fundamental of NASA's sample return missions because it is expected to provide insight into the initial elemental and isotopic composition of the solar nebula from which all other planetary objects formed. The data from this mission will have a large impact on understanding the origins and diversity of planetary materials. The collectors consist of clean, pure materials into which the solar wind will imbed. Science and engineering issues such as bulk purity, cleanliness, retention of solar wind, and ability to withstand launch and entry drove material choices. Most of the collector materials are installed on array frames that are deployed from a clean science canister. Two of the arrays are continuously exposed for collecting the bulk solar wind; the other three are only exposed during specific solar wind regimes as measured by ion and electron monitors. Other materials are housed as targets at the focal point of an electrostatic mirror, or "concentrator", designed to enhance the flux of specific solar wind species. Johnson Space Center (JSC) has two principal responsibilities for the Genesis mission: contamination control and curation. Precise and accurate measurements of the composition of the solar atoms require that the collector materials be extremely clean and well characterized before launch and during the mission. Early involvement of JSC curation personnel in concept development resulted in a mission designed to minimize contaminants from the spacecraft and operations. A major goal of the Genesis mission is to provide a reservoir of materials for the 21 51 century. When the collector materials are returned to Earth, they must be handled in a clean manner and their condition well documented. Information gained in preliminary examination of the arrays and detailed surveys of each collector will be used to guide sample allocations to the scientific community. Samples allocated for analysis are likely to be small sections of individual collectors, therefore subdividing the materials must take place in a clean, well characterized way. A major focus of current research at JSC includes identifying and characterizing the contamination, waste, and alteration of the sample when using different subdividing, transport, and storage techniques and developing protocols for reducing their impact on the scientific integrity of the mission.

Stansbery, E. K.↗
NASA NTRS2016

The 2 Pi Charged Particles Analyzer: All-Sky Camera Concept and Development for Space Missions

Increasing the temporal resolution and instant coverage of velocity space of space plasma measurements is one of the key issues for experimentalists. Today, the top-hat plasma analyzer appears to be the favorite solution due to its relative simplicity and the possibility to extend its application by adding a mass-analysis section and an electrostatic angular scanner. Similarly, great success has been achieved in MMS mission using such multiple top-hat analyzers to achieve unprecedented temporal resolution. An instantaneous angular coverage of charged particles measurements is an alternative approach to pursuing the goal of high time resolution. This was done with 4-D Fast Omnidirectional Nonscanning Energy Mass Analyzer and, to a lesser extent, by DYMIO instruments for Mars-96 and with the Fast Imaging Plasma Spectrometer instrument for MErcury Surface, Space ENvironment, GEochemistry, and Ranging mission. In this paper we describe, along with precursors, a plasma analyzer with a 2 electrostatic mirror that was developed originally for the Phobos-Soil mission with a follow-up in the frame of the BepiColombo mission and is under development for future Russian missions. Different versions of instrument are discussed along with their advantages and drawbacks.

Vaisberg, O.↗
NASA NTRS2006

A Novel Concept for a Deformable Membrane Mirror for Correction of Large Amplitude Aberrations

Very large, light weight mirrors are being developed for applications in space. Due to launch mass and volume restrictions these mirrors will need to be much more flexible than traditional optics. The use of primary mirrors with these characteristics will lead to requirements for adaptive optics capable of correcting wave front errors with large amplitude relatively low spatial frequency aberrations. The use of low modulus membrane mirrors actuated with electrostatic attraction forces is a potential solution for this application. Several different electrostatic membrane mirrors are now available commercially. However, as the dynamic range requirement of the adaptive mirror is increased the separation distance between the membrane and the electrodes must increase to accommodate the required face sheet deformations. The actuation force applied to the mirror decreases inversely proportional to the square of the separation distance; thus for large dynamic ranges the voltage requirement can rapidly increase into the high voltage regime. Experimentation with mirrors operating in the KV range has shown that at the higher voltages a serious problem with electrostatic field cross coupling between actuators can occur. Voltage changes on individual actuators affect the voltage of other actuators making the system very difficult to control. A novel solution has been proposed that combines high voltage electrodes with mechanical actuation to overcome this problem. In this design an array of electrodes are mounted to a backing structure via light weight large dynamic range flextensional actuators. With this design the control input becomes the separation distance between the electrode and the mirror. The voltage on each of the actuators is set to a uniform relatively high voltage, thus the problem of cross talk between actuators is avoided and the favorable distributed load characteristic of electrostatic actuation is retained. Initial testing and modeling of this concept demonstrates that this is an attractive concept for increasing the dynamic range capability of electrostatic deformable mirrors.

Moore, Jim↗
NASA NTRS1983

Static shape forming for an electrostatically controlled membrane mirror

A design concept is described permitting the static construction of a flexible membrane reflector for use in a radiometer spacecraft. The scheme utilizes electrostatic forces to actively shape the membrane toward a specified reflector surface with a required degree of precision. The formulations of the required electrostatic attractive forces, and stress and strain distributed in the membrane are presented in this paper in terms of curvilinear coordinates. An example is given to illustrate a variety of spherical membrane characteristics associated with different boundary conditions.

Juang, J. N.↗
NASA NTRS1996

Computation of Static Shapes and Voltages for Micromachined Deformable Mirrors with Nonlinear Electostatic Actuators

In modeling micromachined deformable mirrors with electrostatic actuators whose gap spacings are of the same order of magnitude as that of the surface deformations, it is neccessary to use nonlinear models for the actuators. In this paper, we consider micromachined deformable mirrors modeled by a membrane or plate equation with nonlinear electrostatic actuator characteristics.

deformations optical systems adaptive optical syst↗