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NASA NTRS1999

A Method for Assessing Material Flammability for Micro-Gravity Environments

On a spacecraft, one of the greatest fears during a mission is the outbreak of a fire. Since spacecraft are enclosed spaces and depend highly on technical electronics, a small fire could cause a large amount of damage. NASA uses upward flame spread as a "worst case scenario" evaluation for materials and the Heat and Visible Smoke Release Rates Test to assess the damage potential of a fire. Details of these tests and the protocols followed are provided by the "Flammability, Odor, Offgassing, and Compatibility Requirements and Test Procedures for Materials in Environments that Support Combustion" document. As pointed by Ohlemiller and Villa, the upward flame spread test does not address the effect of external radiation on ignition and spread. External radiation, as that coming from an overheated electrical component, is a plausible fire scenario in a space facility and could result in a reversal of the flammability rankings derived from the upward flame spread test. The "Upward Flame Propagation Test" has been the subject of strong criticism in the last few years. In many cases, theoretical exercises and experimental results have demonstrated the possibility of a reversal in the material flammability rankings from normal to micro-gravity. Furthermore, the need to incorporate information on the effects of external radiation and opposed flame spread when ranking materials based on their potential to burn in micro-gravity has been emphasized. Experiments conducted in a 2.2 second drop tower with an ethane burner in an air cross flow have emphasized that burning at the trailing edge is deterred in micro-gravity due to the decreased oxygen transport. For very low air flow velocities (U<0.005 m/s) the flame envelopes the burner and a slight increase in velocity results in extinction of the trailing edge (U>0.01 m/s). Only for U>0.l m/s extinction is observed at the leading edge (blow-off). Three dimensional numerical calculations performed for thin cellulose centrally ignited with an axisymmetric source have shown that under the presence of a forced flow slower than 0.035 m/s flames spreads only opposing the flow. Extinction is observed at the trailing edge with no concurrent propagation. Experiments conducted by the same authors at the JAMIC 10 second drop tower verified these calculations. Reducing the oxygen supply to the flame also results in a decrease of the Damk6hler number which might lead to extinction. Greyson et al. and Ferkul conducted experiments in micro-gravity (5 second drop tower) with thin paper and observed that at very low flow velocities concurrent flame spread will stop propagating and the flame will reduce in size and extinguish. They noted that quenching differs significantly from blow-off in that the upstream leading edge will remain anchored to the burn out edge.

Steinhaus, T.↗

NASA NTRS2000

Development of Individually Addressable Micro-Mirror-Arrays for Space Applications

We have been developing a 32 x 32 prototype array of individually addressable Micro-Mirrors capable of operating at cryogenic temperature for Earth and Space Science applications. Micro-Mirror-Array technology has the potential to revolutionize imaging and spectroscopy systems for NASA's missions of the 21st century. They can be used as programmable slits for the Next Generation Space Telescope, as smart sensors for a steerable spectrometer, as neutral density filters for bright scene attenuation etc. The, entire fabrication process is carried out in the Detector Development Laboratory at NASA, GSFC. The fabrication process is low temperature compatible and involves integration of conventional CMOS technology and surface micro-machining used in MEMS. Aluminum is used as the mirror material and is built on a silicon substrate containing the CMOS address circuit. The mirrors are 100 microns x l00 microns in area and deflect by +/- 10 deg induced by electrostatic actuation between two parallel plate capacitors. A pair of thin aluminum torsion straps allow the mirrors to tilt. Finite-element-analysis and closed form solutions using electrostatic and mechanical torque for mirror operation were developed and the results were compared with laboratory performance. The results agree well both at room temperature and at cryogenic temperature. The development demonstrates the first cryogenic operation of two-dimensional Micro-Mirrors with bi-state operation. Larger arrays will be developed meeting requirements for different science applications. Theoretical analysis, fabrication process, laboratory test results and different science applications will be described in detail.

Dutta, Sanghamitra B.↗

NASA NTRS1998

MEMS Micro-Valve for Space Applications

We report on the development of a Micro-ElectroMechanical Systems (MEMS) valve that is designed to meet the rigorous performance requirements for a variety of space applications, such as micropropulsion, in-situ chemical analysis of other planets, or micro-fluidics experiments in micro-gravity. These systems often require very small yet reliable silicon valves with extremely low leak rates and long shelf lives. Also, they must survive the perils of space travel, which include unstoppable radiation, monumental shock and vibration forces, as well as extreme variations in temperature. Currently, no commercial MEMS valve meets these requirements. We at JPL are developing a piezoelectric MEMS valve that attempts to address the unique problem of space. We begin with proven configurations that may seem familiar. However, we have implemented some major design innovations that should produce a superior valve. The JPL micro-valve is expected to have an extremely low leak rate, limited susceptibility to particulates, vibration or radiation, as well as a wide operational temperature range.

Chakraborty, I.↗

NASA NTRS1999

Enhanced Boiling on Micro-Configured Composite Surfaces Under Microgravity Conditions

In order to accommodate the growing thermal management needs of future space platforms, several two-phase active thermal control systems (ATCSs) have evolved and were included in the designs of space stations. Compared to the pumped single-phase liquid loops used in the conventional Space Transportation System and Spacelab, ATCSs offer significant benefits that may be realized by adopting a two-phase fluid-loop system. Alternately, dynamic power systems (DPSs), based on the Rankine cycle, seem inevitably to be required to supply the electrical power requirements of expanding space activities. Boiling heat transfer is one of the key technologies for both ATCSs and DPSs. Nucleate boiling near critical heat flux (CHF) can transport very large thermal loads with much smaller device size and much lower pumping power. However, boiling performance deteriorates in a reduced gravity environment and operation in the CHF regime is precarious because any slight overload will cause the heat transfer to suddenly move to the film boiling regime, which in turn, will result in burnout of the heat transfer surfaces. New materials, such as micro-configured metal-graphite composites, can provide a solution for boiling enhancement. It has been shown experimentally that this type of material manifests outstanding boiling heat transfer performance and their CHF is also extended to higher values. Due to the high thermal conductivity of graphite fiber (up to 1,200 W/m-K in the fiber direction), the composite surfaces are non-isothermal during the boiling process. The composite surfaces are believed to have a much wider safe operating region (a more uniform boiling curve in the CHF regime) because non-isothermal surfaces have been found to be less sensitive to variations of wall superheat in the CHF regime. The thermocapillary forces formed by the temperature difference between the fiber tips and the metal matrix play a more important role than the buoyancy in the bubble detachment, for the bubble detachment manifests itself by a necking process which should not be weakened by reduced gravity. In addition, the composite surfaces introduce no extra pressure drop, no fouling and do not impose significant primary or maintenance costs. All of these suggest that this type of composite is an ideal material for the challenge of accounting for both reliability and economy of the relevant components applied in the ATCSs, the DPSs and other devices in future space missions. The aim of the proposed work is to experimentally investigate high nucleate pool boiling performance on a micro-configured metal-graphite composite surface and to determine the mechanisms of the nucleate boiling heat transfer both experimentally and theoretically. Freon-113 and water will be used as the test liquids to investigate wettability effects on boiling characteristics. The Cu-Gr and Al-Gr composites with various volume fractions of graphite fibers will be tested to obtain the heat transfer characteristic data in the nucleate boiling region and in the CHF regime. In the experiments, the bubble emission and coalescence processes will be recorded by a video camera with a magnifying borescope probe immersed in the working fluid. The temperature profile in the thermal boundary layer on the composite surfaces will be measured by a group of micro thermocouples consisting of four ultra fine micro thermocouples. This instrument was developed and successfully used to measure the temperature profile of evaporating liquid thin layers by the proposers in a study performed at the NASA/Lewis Research Center. A two tier model to explain the nucleate boiling process and the performance enhancement on the composite surfaces has been suggested by the authors. According to the model, the thicknesses of the microlayer and the macrolayer underneath the bubbles and mushrooms, can be estimated by the geometry of the composite surface. The experimental results will be compared to the predictions from the model, and in turn, to revise and improve it.

Zhang, Nengli↗

NASA NTRS2002

Optimal Micro-Scale Secondary Flow Control for the Management of High Cycle Fatigue and Distortion in Compact Inlet Diffusers

The purpose of this study on micro-scale secondary flow control (MSFC) is to study the aerodynamic behavior of micro-vane effectors through their factor (i.e., the design variable) interactions and to demonstrate how these statistical interactions, when brought together in an optimal manner, determine design robustness. The term micro-scale indicates the vane effectors are small in comparison to the local boundary layer height. Robustness in this situation means that it is possible to design fixed MSFC robust installation (i.e.. open loop) which operates well over the range of mission variables and is only marginally different from adaptive (i.e., closed loop) installation design, which would require a control system. The inherent robustness of MSFC micro-vane effector installation designs comes about because of their natural aerodynamic characteristics and the manner in which these characteristics are brought together in an optimal manner through a structured Response Surface Methodology design process.

Anderson, Bernhard H.↗

NASA NTRS2004

Space Technology 5: Pathfinder for Future Micro-Sat Constellations

The Space Technology 5 (ST-5) Project, currently in the implementation phase, is part of the National Aeronautics and Space Administration (NASA) s New Millennium Program (NMP). ST-5 will consist of a constellation of three miniature satellites, each with mass less than 25 kg and size approximately 60 cm by 30 cm. ST-5 addresses technology challenges, as well as fabrication, assembly, test and operations strategies for future micro-satellite missions. ST-5 will be deployed into a highly eccentric, geo-transfer orbit (GTO). This will expose the spacecraft to a high radiation environment as well as provide a low level magnetic background. A three-month flight demonstration phase is planned to validate the technologies and demonstrate concepts for future missions. Each ST-5 spacecraft incorporates NMP competitively-selected breakthrough technologies. These include Cold Gas Micro-Thrusters for propulsion and attitude control, miniature X-band transponder for space-ground communications, Variable Emittance Coatings for dynamic thermal control, and CULPRiT ultra low power logic chip used for Reed-Solomon encoding. The ST-5 spacecraft itself is a technology that can be infused into future missions. It is a fully functional micro-spacecraft built within tight volume and mass constraints. It is built to withstand a high radiation environment, large thermal variations, and high launch loads. The spacecraft power system is low-power and low-voltage, and is designed to turn on after separation &om the launch vehicle. Some of the innovations that are included in the ST-5 design are a custom spacecraft deployment structure, magnetometer deployment boom, nutation damper, X-band antenna, miniature spinning sun sensor, solar array with triple junction solar cells, integral card cage assembly containing single card Command and Data Handling and Power System Electronics, miniature magnetometer, and lithium ion battery. ST-5 will demonstrate the ability of a micro satellite to perform research-quality science. Each ST-5 spacecraft will deploy a precision magnetometer to be used both for attitude determination and as a representative science instrument. The spacecraft has been developed with a low magnetic signature to avoid interference with the magnetometer. The spacecraft will be able to detect and respond autonomously to science events, i.e. significant changes in the magnetic field measurements. The three spacecraft will be a pathfinder for future constellation missions. They will be deployed to demonstrate an appropriate geometry for scientific measurements as a constellation. They will be operationally managed as a constellation, demonstrating automation and communication strategies that will be useful for future missions. The technologies and future mission concepts will be validated both on the ground and in space. Technologies will be validated on the ground by a combination of component level and system level testing of the flight hardware in a thermal vacuum environment. In flight, specific validation runs are planned for each of the technologies. Each validation run consists of one or more orbits with a specific validation objective. This paper will describe the ST-5 mission, and the applicability of the NMP technologies, spacecraft, and mission concepts to future missions. It will also discuss the validation approach for the ST-5 technologies and mission concepts.

Carlisle, Candace↗

NASA NTRS2004

Development of Micro Air Vehicle Technology With In-Flight Adaptive-Wing Structure

This is a final report on the research studies, "Development of Micro Air Vehicle Technology with In-Flight Adaptrive-Wing Structure". This project involved the development of variable-camber technology to achieve efficient design of micro air vehicles. Specifically, it focused on the following topics: 1) Low Reynolds number wind tunnel testing of cambered-plate wings. 2) Theoretical performance analysis of micro air vehicles. 3) Design of a variable-camber MAV actuated by micro servos. 4) Test flights of a variable-camber MAV.

Waszak, Martin R.↗

NASA NTRS2004

Electric-field-driven Phenomena for Manipulating Particles in Micro-Devices

Compared to other available methods, ac dielectrophoresis is particularly well-suited for the manipulation of minute particles in micro- and nano-fluidics. The essential advantage of this technique is that an ac field at a sufficiently high frequency suppresses unwanted electric effects in a liquid. To date very little has been achieved towards understanding the micro-scale field-and shear driven behavior of a suspension in that, the concepts currently favored for the design and operation of dielectrophoretic micro-devices adopt the approach used for macro-scale electric filters. This strategy considers the trend of the field-induced particle motions by computing the spatial distribution of the field strength over a channel as if it were filled only with a liquid and then evaluating the direction of the dielectrophoretic force, exerted on a single particle placed in the liquid. However, the exposure of suspended particles to a field generates not only the dielectrophoretic force acting on each of these particles, but also the dipolar interactions of the particles due to their polarization. Furthermore, the field-driven motion of the particles is accompanied by their hydrodynamic interactions. We present the results of our experimental and theoretical studies which indicate that, under certain conditions, these long-range electrical and hydrodynamic interparticle interactions drastically affect the suspension behavior in a micro-channel due to its small dimensions.

Khusid, Boris↗

NASA NTRS2004

Space Technology 5: Enabling Future Micro-Sat Constellation Science Missions

The Space Technology 5 (ST-5) Project is part of NASA s New Millennium Program. ST-5 will consist of a constellation of three micro-satellites, each approximately 25 kg in mass. The mission goals are to demonstrate the research-quality science capability of the ST-5 spacecraft; to operate the three spacecraft as a constellation; and to design, develop and flight-validate three capable micro-satellites with new technologies. ST-5 is designed to measurably raise the utility of small satellites by providing high functionality in a low mass, low power, and low volume package. The whole of ST-5 is greater than the sum of its parts: the collection of components into the ST-5 spacecraft allows it to perform the functionality of a larger scientific spacecraft on a micro-satellite platform. The ST-5 mission was originally designed to be launched as a secondary payload into a Geosynchronous Transfer Orbit (GTO). Recently, the mission has been replanned for a Pegasus XL dedicated launch into an elliptical polar orbit. A three-month flight demonstration phase, beginning in March 2006, will validate the ability to perform science measurements, as well as the technologies and constellation operations. ST- 5 s technologies and concepts will then be transferred to future micro-sat science missions.

Carlisle, Candace C.↗

NASA NTRS2004

Space Technology 5: Enabling Future Micro-Sat Constellation Science Missions

The Space Technology 5 (ST-5) Project is part of NASA s New Millennium Program. ST-5 will consist of a constellation of three micro-satellites, each approximately 25 kg in mass. The mission goals are to demonstrate the research-quality science capability of the ST-5 spacecraft, to operate the three spacecraft as a constellation; and to design, develop and flight-validate three capable micro-satellites with new technologies. ST-5 is designed to measurably raise the utility of small satellites by providing high functionality in a low mass, low power, and low volume package. The whole of ST-5 is greater than the sum of its parts: the collection of components into the ST-5 spacecraft allows it to perform the functionality of a larger scientific spacecraft on a micro-satellite platform. The ST-5 mission was originally designed to be launched as a secondary payload into a Geosynchronous Transfer Orbit (GTO). Recently, the mission has been replanned for a Pegasus XL dedicated launch into an elliptical polar orbit. A three-month flight demonstration phase, beginning in March 2006, will validate the ability to perform science measurements, as well as the technologies and constellation operations. ST- 5 s technologies and concepts will then be transferred to future micro-sat science missions.

Carlisle, Candace C.↗

NASA NTRS2005

Sub-Grid Modeling of Electrokinetic Effects in Micro Flows

Advances in micro-fabrication processes have generated tremendous interests in miniaturizing chemical and biomedical analyses into integrated microsystems (Lab-on-Chip devices). To successfully design and operate the micro fluidics system, it is essential to understand the fundamental fluid flow phenomena when channel sizes are shrink to micron or even nano dimensions. One important phenomenon is the electro kinetic effect in micro/nano channels due to the existence of the electrical double layer (EDL) near a solid-liquid interface. Not only EDL is responsible for electro-osmosis pumping when an electric field parallel to the surface is imposed, EDL also causes extra flow resistance (the electro-viscous effect) and flow anomaly (such as early transition from laminar to turbulent flow) observed in pressure-driven microchannel flows. Modeling and simulation of electro-kinetic effects on micro flows poses significant numerical challenge due to the fact that the sizes of the double layer (10 nm up to microns) are very thin compared to channel width (can be up to 100 s of m). Since the typical thickness of the double layer is extremely small compared to the channel width, it would be computationally very costly to capture the velocity profile inside the double layer by placing sufficient number of grid cells in the layer to resolve the velocity changes, especially in complex, 3-d geometries. Existing approaches using "slip" wall velocity and augmented double layer are difficult to use when the flow geometry is complicated, e.g. flow in a T-junction, X-junction, etc. In order to overcome the difficulties arising from those two approaches, we have developed a sub-grid integration method to properly account for the physics of the double layer. The integration approach can be used on simple or complicated flow geometries. Resolution of the double layer is not needed in this approach, and the effects of the double layer can be accounted for at the same time. With this approach, the numeric grid size can be much larger than the thickness of double layer. Presented in this report are a description of the approach, methodology for implementation and several validation simulations for micro flows.

Chen, C. P.↗

NASA NTRS1996

Micro heat pipe panels and method for producing same

Flat or curved micro heat pipe panels are fabricated by arranging essentially parallel filaments in the shape of the desired panel. The configuration of the filaments corresponds to the desired configuration of the tubes that will constitute the heat pipes. A thermally conductive material is then deposited on and around the filaments to fill in the desired shape of the panel. The filaments are then removed, leaving tubular passageways of the desired configuration and surface texture in the material. The tubes are then filled with a working fluid and sealed. Composite micro heat pipe laminates are formed by layering individual micro heat pipe panels and bonding them to each other to form a single structure. The layering sequence of the micro heat pipe panels can be tailored to transport heat preferentially in specific directions as desired for a particular application.

Camarda, Charles J.↗

NASA NTRS1997

Method for producing micro heat panels

Camarda, Charles J.↗

NASA NTRS2007

Space Technology 5 - A Successful Micro-Satellite Constellation Mission

The Space Technology 5 (ST5) constellation of three micro-satellites was launched March 22, 2006. During the three-month flight demonstration phase, the ST5 team validated key technologies that will make future low-cost micro-sat constellations possible, demonstrated operability concepts for future micro-sat science constellation missions, and demonstrated the utility of a micro-satellite constellation to perform research-quality science. The ST5 mission was successfully completed in June 2006, demonstrating high-quality science and technology validation results.

Carlisle, Candace↗

NASA NTRS2008

Checking Contamination during Storage of Carbonaceous Chondrites for Micro FTIR Measurements

We examined organic contamination by Fourier transform infrared micro spectroscopic (micro FTIR) measurements of carbonaceous chondrite samples. Carbonaceous chondrites, Tagish Lake (C2), Murchison (CM2) and Moss (CO3), and some mineral powder samples pressed on aluminum plates were measured by micro FTIR before and after storage in several containers with silicone rubber mat. During storage, samples did not touch directly anything except the holding aluminum plates. The carbonaceous chondrites containing hydrous minerals (Tagish Lake and Murchison) pressed on aluminum plates and measured by transmission-reflection micro FTIR measurements were found to be contaminated during storage after only one day, as revealed by an increase of approximately 2965 /cm and approximately 1260 /cm peaks. The Moss meteorite which contains no hydrous minerals, did not show an increase of these peaks, indicating no organic contamination. This difference is probably related to the differing mineralogy and physical properties (including porosity and permeability) of these chondrites. Hydrous minerals such as antigorite, muscovite, montmorillonite and silica gel showed organic contamination by the same infrared measurements, while anhydrous materials such as SiO2 and KBr showed no contamination. These results indicate importance of surface OH groups for the organic contamination. Organic contamination was found on silica gel samples pressed on aluminum plates when they were stored within containers including silicone rubber, silicone grease or adhesive tape. Long path gas cell FTIR measurements for silicone rubber indicated methylsiloxane oligomers were released from the silicone rubber. In-situ heating infrared measurements on the contaminated antigorite and Tagish Lake showed decrease of the 1262 /cm (Si-CH3) and 2963 /cm (CH3) peaks from room temperature to 200-300 C indicating desorption of volatile contaminants. These results indicate that careful preparation and storage are essential for FTIR measurements on precious astromaterial samples such as meteorites, IDPs and samples returned from comets, asteroids and Mars. Every possible contamination source should be evaluated before anything is done to these samples.

Zolensky, Michael E.↗

NASA NTRS2010

Micro-Ramp Flow Control for Oblique Shock Interactions: Comparisons of Computational and Experimental Data

Computational fluid dynamics was used to study the effectiveness of micro-ramp vortex generators to control oblique shock boundary layer interactions. Simulations were based on experiments previously conducted in the 15 x 15 cm supersonic wind tunnel at NASA Glenn Research Center. Four micro-ramp geometries were tested at Mach 2.0 varying the height, chord length, and spanwise spacing between micro-ramps. The overall flow field was examined. Additionally, key parameters such as boundary-layer displacement thickness, momentum thickness and incompressible shape factor were also examined. The computational results predicted the effects of the micro-ramps well, including the trends for the impact that the devices had on the shock boundary layer interaction. However, computing the shock boundary layer interaction itself proved to be problematic since the calculations predicted more pronounced adverse effects on the boundary layer due to the shock than were seen in the experiment.

Hirt, Stefanie M.↗

NASA NTRS2001

Terahertz-Regime, Micro-VEDs: Evaluation of Micromachined TWT Conceptual Designs

Summary form only given. The Terahertz (THz) region of the electromagnetic spectrum (approx.300-3000 GHz) has enormous potential for high-data-rate communications, spectroscopy, astronomy, space research, medicine, biology, surveillance, remote sensing, industrial process control, etc. The most critical roadblock to full exploitation of the THz band is lack of coherent radiation sources that are powerful (0.01-10.0 W continuous wave), efficient (>1 %), frequency agile (instantaneously tunable over 1% bandwidths or more), reliable, and relatively inexpensive. Micro-machined Vacuum Electron Devices (micro-VEDs) represent a promising solution. We describe prospects for miniature, THz-regime TWTs fabricated using micromachining techniques. Several approx.600 GHz conceptual designs are compared. Their expected performance has been analyzed using SD, 2.51), and 3D TWT codes. A folded waveguide (FWG) TWT forward-wave amplifier design is presented based on a Northrop Grumman (NGC) optimized design procedure. This conceptual device is compared to the simulated performance of a novel, micro-VED helix TWT. Conceptual FWG TWT backward-wave amplifiers and oscillators are also discussed. A scaled (100 GHz) FWG TWT operating at a relatively low voltage (-12 kV) is under development at NGC. Also, actual-size micromachining experiments are planned to evaluate the feasibility of arrays of micro-VED TWTs. Progress and results of these efforts are described. This work was supported, in part by AFOSR, ONR, and NSF.

Booske, John H.↗

NASA NTRS2013

Micro-XRF for In Situ Geological Exploration of Other Planets

In situ analysis of rock chemistry is a fundamental tool for exploration of planets. To meet this need, a high-spatial-resolution micro x-ray fluorescence (Micro-XRF) instrument was developed that is capable of determining the elemental composition of rocks (elements Na U) with 100 microns spatial resolution, thus providing insight to the composition of features as small as sand grains and individual laminae. The resulting excitation beam is of sufficient intensity that high signal-to-noise punctual spectra are acquired in seconds to a few minutes using an Amptek Silicon Drift Detector (SDD). The instrument features a tightly focused x-ray tube and HVPS developed by Moxtek that provides up to 200 micro-A at 10 to 50 keV, with a custom polycapillary optic developed by XOS Inc. and integrated into a breadboard Micro-XRF (see figure). The total mass of the complete breadboard instrument is 2.76 kg, including mounting hardware, mounting plate, camera, laser, etc. A flight version of this instrument would require less than 5W nominal power and 1.5 kg mass. The instrument includes an Amptek SDD that draws 2.5 W and has a resolution of 135 to 155 eV FWHM at 5.9 keV. It weighs 180 g, including the preamplifier, digital pulse processor, multichannel analyzer, detector and preamp power supplies, and packaging. Rock samples are positioned relative to the instrument by a three-axis arm whose position is controlled by closed-loop translators (mimicking the robotic arm of a rover). The distance from the source to the detector is calculated from the position of a focused laser beam on the sample as imaged by the camera. The instrument enables quick scans of major elements in only 1 second, and rapid acquisition (30 s) of data with excellent signal-to-noise and energy resolution for trace element analysis

Wade, Lawrence A.↗