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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Performance characterization of a segmented anode arcjet thruster

A modular, 1 to 2 kW class arcjet thruster incorporating a segmented anode/nozzle was operated on a thrust stand to obtain performance characteristics of the device and further study its operating characteristics under a number of experimental conditions. The nozzle was composed of five axial conducting segments isolated from one another by boron nitride spacers. The electrical configuration allowed the current delivered to the arcjet to be collected at any combination of segments. Both the current collected by each segment, and the potential difference between the cathode and each segment were monitored throughout the test period. As in previous tests a similar device, current appeared to attach diffusely in the anode when all of the segments were allowed to conduct. Improvements to the device allowed long term (4 to 8 hour) operation at steady-state and operating characteristics were repeatable over extended periods. Performance characteristics indicated that the segmented anode reasonably simulates the behavior of solid anodes of similar geometry. Current distribution depended on flow rate as the arc attachment moved downstream in the nozzle with increases in the mass flow rate. The current level had little effect on current distribution on the anode segments. Thrust measurements indicated that the current distribution in the nozzle did not significantly affect performance of the device.

Curran, Francis M.↗
NASA NTRS2004

NASA Tech Briefs, June 2004

Topics covered include: COTS MEMS Flow-Measurement Probes; Measurement of an Evaporating Drop on a Reflective Substrate; Airplane Ice Detector Based on a Microwave Transmission Line; Microwave/Sonic Apparatus Measures Flow and Density in Pipe; Reducing Errors by Use of Redundancy in Gravity Measurements; Membrane-Based Water Evaporator for a Space Suit; Compact Microscope Imaging System with Intelligent Controls; Chirped-Superlattice, Blocked-Intersubband QWIP; Charge-Dissipative Electrical Cables; Deep-Sea Video Cameras Without Pressure Housings; RFID and Memory Devices Fabricated Integrally on Substrates; Analyzing Dynamics of Cooperating Spacecraft; Spacecraft Attitude Maneuver Planning Using Genetic Algorithms; Forensic Analysis of Compromised Computers; Document Concurrence System; Managing an Archive of Images; MPT Prediction of Aircraft-Engine Fan Noise; Improving Control of Two Motor Controllers; Electro-deionization Using Micro-separated Bipolar Membranes; Safer Electrolytes for Lithium-Ion Cells; Rotating Reverse-Osmosis for Water Purification; Making Precise Resonators for Mesoscale Vibratory Gyroscopes; Robotic End Effectors for Hard-Rock Climbing; Improved Nutation Damper for a Spin-Stabilized Spacecraft; Exhaust Nozzle for a Multitube Detonative Combustion Engine; Arc-Second Pointer for Balloon-Borne Astronomical Instrument; Compact, Automated Centrifugal Slide-Staining System; Two-Armed, Mobile, Sensate Research Robot; Compensating for Effects of Humidity on Electronic Noses; Brush/Fin Thermal Interfaces; Multispectral Scanner for Monitoring Plants; Coding for Communication Channels with Dead-Time Constraints; System for Better Spacing of Airplanes En Route; Algorithm for Training a Recurrent Multilayer Perceptron; Orbiter Interface Unit and Early Communication System; White-Light Nulling Interferometers for Detecting Planets; and Development of Methodology for Programming Autonomous Agents.

Source record↗
DOE OSTI2024

Oscillating surge wave energy converter using a novel above-water power takeoff with belt-arc speed amplification

We investigate the performance of a novel power takeoff (PTO) featuring belt-arc speed amplification for oscillating surge wave energy converters (OSWECs), aiming to address the challenges of extremely low rotary speed and large torque under the low-frequency ocean wave excitations. The belt-arc design significantly increases the rotary speed of the generator, enabling generator downsizing and decreasing the powertrain friction losses. The design also allows for placing the generator above water, eliminating the need for high Ingress Protection ratings for the generator and powertrain, and potentially leading to substantial reductions in capital and maintenance costs. Using the linear potential wave theory, the dynamics of the integrated system are analyzed, and key parameters are identified. To validate the numerical analysis, a 1:10 scale model is designed, fabricated, and tested in a wave tank. Performance evaluations are conducted under regular and irregular wave conditions, with quantified effects of parameter tuning. The results reveal an optimal wave-to-electric efficiency of 48% under regular wave excitation and 20% under irregular excitation. Furthermore, these findings underscore the effectiveness of the proposed novel PTO design in addressing the challenges of low rotation speed and large torque inherent in OSWECs, demonstrating its ability to efficiently convert wave power into electricity.

16 TIDAL AND WAVE POWER↗
NASA NTRS1980

Near-comet trajectory design

The Halley Flyby/Tempel 2 Rendezvous mission requires not only a new spacecraft design and a new propulsion system (the Solar Electric Propulsion System), but it also requires new approaches to the trajectory and the mission design. Because of the feebleness of Tempel 2 gravitation and because of the presence of various other competing forces, a realization and/or preservation of a spacecraft trajectory about the comet is characteristically different from that about a more massive body. This paper surveys, compares, and evaluates the significance of various forces acting on the spacecraft in the vicinity of the comet. The range of variations and uncertainties inherent in modeling of these forces are also discussed. Then, a number of different types of trajectories relevant to the design of the Tempel 2 exploration are depicted and examined. These include short-arc trajectories, near-comet short- and long-term orbits, and comet-landing trajectories.

Jones, J. B.↗
DOE OSTI2021

Nonlinear nanoelectrodynamics of a Weyl metal

Chiral Weyl fermions with linear energy-momentum dispersion in the bulk accompanied by Fermi-arc states on the surfaces prompt a host of enticing optical effects. While new Weyl semimetal materials keep emerging, the available optical probes are limited. In particular, isolating bulk and surface electrodynamics in Weyl conductors remains a challenge. We devised an approach to the problem based on near-field photocurrent imaging at the nanoscale and applied this technique to a prototypical Weyl semimetal TaIrTe 4 . As a first step, we visualized nano-photocurrent patterns in real space and demonstrated their connection to bulk nonlinear conductivity tensors through extensive modeling augmented with density functional theory calculations. Notably, our nanoscale probe gives access to not only the in-plane but also the out-of-plane electric fields so that it is feasible to interrogate all allowed nonlinear tensors including those that remained dormant in conventional far-field optics. Surface- and bulk-related nonlinear contributions are distinguished through their “symmetry fingerprints” in the photocurrent maps. Robust photocurrents also appear at mirror-symmetry breaking edges of TaIrTe 4 single crystals that we assign to nonlinear conductivity tensors forbidden in the bulk. Here, nano-photocurrent spectroscopy at the boundary reveals a strong resonance structure absent in the interior of the sample, providing evidence for elusive surface states.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2014

Integration of a MicroCAT Propulsion System and a PhoneSat Bus into a 1.5U CubeSat

NASA Ames Research Center and the George Washington University have developed an electric propulsion subsystem that can be integrated into the PhoneSat bus. Experimental tests have shown a reliable performance by firing three different thrusters at various frequencies in vacuum conditions. The three thrusters were controlled by a SmartPhone that was running the PhoneSat software. The subsystem is fully operational and it requires low average power to function (about 0.1 W). The interface consists of a microcontroller that sends a trigger pulses to the PPU (Plasma Processing Unit), which is responsible for the thruster operation. Frequencies ranging from 1 to 50Hz have been tested, showing a strong flexibility. A SmartPhone acts as the main user interface for the selection of commands that control the entire system. The micro cathode arc thruster MicroCAT provides a high 1(sub sp) of 3000s that allows a 4kg satellite to obtain a (delta)V of 300m/s. The system mass is only 200g with a total of volume of 200(cu cm). The propellant is based on a solid cylinder made of Titanium, which is the cathode at the same time. This simplicity in the design avoids miniaturization and manufacturing problems. The characteristics of this thruster allow an array of MicroCATs to perform attitude control and orbital correcton maneuvers that will open the door for the implementation of an extensive collection of new mission concepts and space applications for CubeSats. NASA Ames is currently working on the integration of the system to fit the thrusters and PPU inside a 1.5U CubeSat together with the PhoneSat bus into a 1.5U CubeSat. This satellite is intended to be deployed from the ISS in 2015 and test the functionality of the thrusters by spinning the satellite around its long axis and measure the rotational speed with the phone byros. This test flight will raise the TRL of the propulsion system from 5 to 7 and will be a first test for further CubeSats with propulsion systems, a key subsystem for long duration or interplanetary CubeSat missions.

PhoneSat↗
NASA NTRS1961

Study of a Solar Sensor for use in Space Vehicle Orientation Control Systems

The solar sensor described herein may be used for a variety of space operations requiring solar orientation. The use of silicon solar cells as the sensing elements provides the sensor with sufficient capability to withstand the hazards of a space environment. A method of arranging the cells in a sensor consists simply of mounting them at a large angle to the base. The use of an opaque shield placed between the cells and perpendicular to the base enhances the small-angle sensitivity while adding slightly to the bulk of the sensor. The difference in illumination of these cells as the result of an oblique incidence of the light rays from the reference source causes an electrical error signal which, when used in a battery-bridge circuit, requires a minimum of electrical processing for use in a space-vehicle orientation control system. An error which could occur after prolonged operation of the sensor is that resulting from asymmetrical aging of opposite cells. This could be periodically corrected with a balance potentiometer. A more routine error in the sensor is that produced by reflected earth radiation. This error may be eliminated over a large portion of the operation time by restricting the field of view and, consequently, the capture capability. A more sophisticated method of eliminating this error is to use separate sensors, for capture and fine pointing, along with a switching device. An experimental model has been constructed and tested to yield an output sensitivity of 1.2 millivolts per second of arc with a load resistance of 1,000 ohms and a reference light source of approximately 1,200 foot-candles delivered at the sensor.

Spencer, Paul R.↗
NASA NTRS1994

Magnetotail views at 33R(sub E): IMP 8 magnetometer observations

This paper presents magnetic field vector (B) maps, electric current vector (curl B) maps, magnetic force (JxB) contour maps, and total field contour maps covering the full tail cross section in the yz plane. The maps are based on 16 years of 5-min averages of Interplanetary Monitoring Platform (IMP) 8 magnetic field data. During this time, IMP 8 traversed the tail between -25R(sub E) and -40R(sub E) in the x direction. Its average x distance was -33R(sub E). For this average distance we show separate maps for low and high dipole tilts, corresponding to equinox and northern hemisphere summer seasons. The low-tilt (equinox) maps show symmetrical field and current patterns; the high-tilt (solstice) maps show the cross-tail current sheet arcing above the equatorial diagonal in the center and dipping below it on the flanks. The shape of warped current sheet fits Fairfield's (1980) displaced ellipse model fairly well. The distance at which the current sheet is hinged to the magnetic equator is found to be 9.88R(sub E) and is independent of Kp. The z profile of current density shows a central peak, 3R(sub E) full width at half maximum, and smaller, flanking shoulders. A Harris sheet profile with a 7R(sub E) thickness fits the B(sub x) profile. Though these are magnetic field data, the JxB maps clearly outline the plasma sheet. This approach also gives 7R(sub E) thickness. Many of the average field and current features inferred and demonstrated in earlier studies are confirmed here; some of them are seen for the first time in full cross-section view. Among new features revealed are a large current vortex in the winter hemisphere lobe, a dawn-dusk asymmetry in the JxB force in the plasma sheet (it is stronger on the duskside), and a separation of the cross-tail current sheet into core and wing parts.

Kaymaz, Zerefsan↗
NASA NTRS2014

Modular Pulsed Plasma Electric Propulsion System for Cubesats

Current capabilities of CubeSats must be improved in order to perform more ambitious missions. Electric propulsion systems will play a key role due to their large specific impulse. Compared to other propulsion alternatives, their simplicity allows an easier miniaturization and manufacturing of autonomous modules into the nano and pico-satellite platform. Pulsed Plasma Thrusters (PPTs) appear as one of the most promising technologies for the near term. The utilization of solid and non-volatile propellants, their low power requirements and their proven reliability in the large scale make them great candidates for rapid implementation. The main challenges are the integration and miniaturization of all the electronic circuitry into a printed circuit board (PCB) that can satisfy the strict requirements that CubeSats present. NASA Ames and the George Washington University have demonstrated functionality and control of three discrete Micro-Cathode Arc Thrusters (CAT) using a bench top configuration that was compatible with the ARC PhoneSat Bus. This demonstration was successfully conducted in a vaccum chamber at the ARC Environmental Test Laboratory. A new effort will integrate a low power Plasma Processing Unit and two plasma thrusters onto a single printed circuit board that will utilize less than 13 U of Bus volume. The target design will be optimized for the accommodation into the PhoneSatEDISON Demonstration of SmallSatellite Networks (EDSN) bus as it uses the same software interface application, which was demonstrated in the previous task. This paper describes the design, integration and architecture of the proposed propulsion subsystem for a planned Technology Demonstration Mission. In addition, a general review of the Pulsed Plasma technology available for CubeSats is presented in order to assess the necessary challenges to overcome further development.

PCB↗
DOE OSTI2025

Sm 2 Ru 3 Sn 5 : A Noncentrosymmetric Cubic Member of the Ln 2 M 3 X 5 Family

An optimized synthetic method is presented for Sm 2 Ru 3 Sn 5 and investigate its physical properties and electronic structure. Sm 2 Ru 3 Sn 5 is prepared by arc-melting stoichiometric ratios of the elements and is confirmed by single crystal and powder X-ray diffraction. An antiferromagnetic transition is observed at T N = 3.8 K. A modified Curie-Weiss fit to the data in the range 50–150 K yields a Curie-Weiss temperature: θ CW = −36.6 K and an effective magnetic moment: μ eff = 0.83 μ B , in agreement with a Sm 3+ oxidation state. Field-dependent magnetization up to H = 7 T at 2 K shows a maximum response of 0.06 μ B , which is significantly lower than the expected Sm 3+ saturation moment (0.71 μ B ). Resistivity measurements indicate metallic behavior, and analysis of the magnetic entropy from the heat capacity reveals a doublet ground state due to crystal electric field splitting. The electronic structure and density of states are calculated with density function theory and further supported by the local density approximation with dynamical mean-field theory. Finally, the experimental and computational results highlight localized Sm 3+ moments and suggest a possible interplay between Ruddelman–Kitel–Kasuya–Yosida and Kondo interactions, positioning Sm 2 Ru 3 Sn 5 as a promising material for studying topology and complex physical phenomena.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Molten Salt Reactor Signatures and Modeling Study

Molten salt reactor (MSR) technologies, either liquid fueled and cooled or only liquid cooled, pose specific, unique challenges for safeguards of the special nuclear material during the operation, fueling, and maintenance of the reactor. MSRs are one type of Generation IV technologies being invested in and considered for U.S. domestic fabrication primarily for electricity and process heat production. These designs have generated growing commercial interest for several reasons, including high (≈40%) thermal efficiency, ease of fueling, improved use of uranium fuel, potential utilization of thorium fuel, and proposed inherent safety features. U.S. companies have several planned designs that differ in fuel, cooling, and neutron energy spectrum. Driven by commercial interest and the intent of licensing MSRs, the U.S. Nuclear Regulatory Commission (NRC) has developed a vision and strategy to accommodate non-light water reactors (LWR), which include MSRs (U.S. Nuclear Regulatory Commission 2019). In addition, the Department of Energy (DOE) through the Office of Nuclear Energy (NE) Office of Advanced Reactor Technologies (ART), …sponsors research, development and deployment (RD&D) activities through its Next Generation Nuclear Plant (NGNP), Advanced Reactor Concepts (ARC), and Advanced Small Modular Reactor (aSMR) programs to promote safety, technical, economical, and environmental advancements of innovative Generation IV nuclear energy technologies. Reactor types considering the use of salts, liquid metals, or gases for coolant fall under both ARC and aSMR. Therefore, Research Design & Development is being pursued by DOE-NE through national laboratories, universities, and international and industrial collaborations. Additionally, the U.S. is a member of the Gen IV International Forum (GIF). The GIF is a cooperative, multinational organization to guide and carry out research and development needed for the GEN IV reactor systems (Forum 2018). GIF evaluated numerous reactor concepts and down-selected to the six most feasible advanced reactor technologies: gas-cooled fast reactor (GFR), lead-cooled fast reactor (LFR), MSR, supercritical watercooled reactor (SCWR), sodium-cooled fast reactor (SFR), and very high temperature reactor (VHTR). In support of the growing interest domestically and internationally, the Materials Protection, Accounting, and Control Technologies (MPACT) campaign, under the DOE-NE Fuel Cycle Technologies (FCT) program, engages in R&D activities by developing advanced instrumentation and analysis for safeguards and security of modern, advanced nuclear fuel cycle (non-LWR) facilities. Because of the historic experience in the operation of the Aircraft Reactor Experiment (ARE) and the Molten Salt Reactor Experiment (MSRE) (Robertson, MSRE Design and Operations Report Part I 1965), Oak Ridge National Laboratory (ORNL) is heavily engaged in the various R&D activities through the DOE complex related to MSRs including national technical leadership of the DOE-NE MSR campaign. This report discusses and presents the outcomes of the FY19 MPACT MSR Safeguards task. The challenges presented by MSRs for nuclear material accountancy and control (NMAC) and associated safeguards will be investigated. The objective of this research is to explore and compile the safeguards requirements and identify measurement signatures through an initial high-level MSR design and develop complementary advanced simulation and modeling capabilities. A high-level ORNL-developed MSR design called the Molten Salt Demonstration Reactor (MSDR) (Bettis, Alexander and Watts 1972) was used as the target reactor design for this research. The MSDR model incorporates technology from the MSRE and the Molten Salt Breeder Reactor (Robertson, Conceptual Design of a Single-Fluid Molten-Salt Breeder Reactor 1971). But the MSDR is a 750 MWth graphite moderated liquid fueled (low-enriched uranium) MSR compared to the MSRE’s of 7.5 MWth. The focus of this report is to discuss the evaluation of novel signatures, correlations, and indicators to understand the applicability of current safeguards instrumentation to MSRs using the modeling results from the MSDR.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
NASA NTRS1979

Two-dimensional potential double layers and discrete auroras

This paper is concerned with the formation of the acceleration region for electrons which produce the visible auroral arc and with the formation of the inverted V precipitation region. The former is embedded in the latter, and both are associated with field-aligned current sheets carried by plasma sheet electrons. It is shown that an electron current sheet driven from the plasma sheet into the ionosphere leads to the formation of a two-dimensional potential double layer. For a current sheet of a thickness less than the proton gyrodiameter solutions are obtained in which the field-aligned potential drop is distributed over a length much greater than the Debye length. For a current sheet of a thickness much greater than the proton gyrodiameter solutions are obtained in which the potential drop is confined to a distance on the order of the Debye length. The electric field in the two-dimensional double-layer model is the zeroth-order field inherent to the current sheet configuration, in contrast to those models in which the electric field is attributed to the first-order field due to current instabilities or turbulences. The maximum potential in the two-dimensional double-layer models is on the order of the thermal energy of plasma sheet protons, which ranges from 1 to 10 keV.

Kan, J. R.↗
DOE OSTI2023

THz Plasmonics and Topological Optics of Weyl Semimetals

THz magneto-optical properties of 3D topological Weyl semimetals were investigated with both THz spectroscopy and THz pump-probe measurements. The unique THz effects predicted in these materials may have important applications in THz technology. The electronic band structure was characterized spectroscopically through THz zero-field reflectance and/or cyclotron resonance measurements. The studies included the dynamic chiral pumping and the study of the predicted novel magneto-electric effects arising from the underlying Berry curvature and magneto plasmonic-like effects in the absence of an applied magnetic field. Chiral pumping in the extreme quantum limit was studied on Weyl semimetals to directly probe the chiral N=0 Landau level. Non-linear pump-probe measurements were used to measure the chiral pumping lifetime. Solids with topologically robust electronic states exhibit unusual electronic and optical transport properties that do not exist in other materials. A particularly interesting example is chiral charge pumping, the so-called chiral anomaly, in recently discovered topological Weyl and Dirac semimetals, where simultaneous application of parallel DC electric and magnetic fields creates an imbalance in the number of carriers of opposite topological charge (chirality). In an earlier study we investigated the Weyl metals Na 3 Bi and Cd 3 As 2 . In this grant we followed up with magneto-optical studies of TaAs, another Weyl semimetal. More recently, we have also characterized other Weyl and Dirac systems that have come on line. The Physics community is still looking for the “hydrogen atom” of the Weyl semimetal. CoSi is one promising new system which features Weyl node spacing comparable to the Brillouin zone size. This system may be suitable for study of the predicted chiral plasmons that arise from the Berry curvature in Weyl materials. In other experiments gates can be applied to the samples in order to study the Fermi arc surface states by modulation reflectance spectroscopy at THz frequencies.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Superconductivity in WBe 2

WBe 2 , which occurs in space group 194, with hexagonal symmetry P6 3 /mmc, is prepared by arc-melting at temperatures above 2200 C, where Be vapor loss is significant. This study is motivated by recent work on MoB 2 and WB 2 , both superconductors (T c =32 and 17 K respectively) under high (∼70 GPa) pressure. In order to avoid the known Be-rich superconducting phases (WBe 13 and WBe 22 ) in the complex phase diagram, both known to be superconducting at 4.1 K, the sample was prepared with a slight (∼5 %) excess of W. The resultant sample, prepared using high purity (99.999 %) Be, is essentially single phase WBe 2 , with some spread in its superconducting properties due to the known homogeneity range. (WBe 2 forms in space group 194 between approximately W 1.02 Be 1.98 and W 0.88 Be 2.12 .) Characterization was carried out with x-ray diffraction, electrical resistivity, ρ, in zero and applied magnetic fields, and specific heat. The resistivity in zero and applied fields and specific heat data indicate that our sample of WBe 2 is a bulk superconductor at ambient pressure with a T c onset in ρ at 1.05 K, and T c (ρ→0) at ∼0.86 K. Furthermore, there is no signature of superconductivity in ρ at 4.1 K, indicating successful avoidance of WBe 13 and WBe 22 . The ρ data in field indicate an upper critical field of approximately 400 gauss.

Electrical transport↗
DOE OSTI2022

Role of Eu-Doping in the Electron Transport Behavior in the Zintl Thermoelectric Ca 5-x-y Yb x Eu y Al 2 Sb 6 System

A series of Eu-doped Zintl compounds belonging to theCa 5-x-y Yb x Eu y Al 2 Sb 6 (x = 0, 1.12; 0 ≤ y ≤ 0.63(2)) system have been successfully synthesized by both the arc-melting and the molten Pb-flux methods. All of the five title compounds initially crystallized in the Ca 5 Ga 2 As 6 -type phase (space group Pbam, Z = 2, Pearson code oP26) and maintained their original structure even after the post-heat treatment, unlike the recently reported n-type Zintl analogues in the Ca 5-x-y Yb x RE y Al 2 Sb 6 (RE = Pr, Nd, Sm) systems, which underwent a phase transition from the Ca 5 Ga 2 As 6 -type to the Ca 5 Al 2 Bi 6 -type phase after annealing. This research aimed to understand the origin of the structural preference of the title Ca 5-x-y Yb x Eu y Al 2 Sb 6 system, whether it was affected by the valence electron count or the cationic size. Electrical transport property measurements showed an increase in electrical conductivities and a decrease of Seebeck coefficients for Ca 4.89(1) Eu 0.11 Al 2 Sb 6 , Ca 4.82(1) Eu 0.18 Al 2 Sb 6 , and Ca 4.62(1) Eu 0.38 Al 2 Sb 6 , compared to the parental compound Ca 5 Al 2 Sb 6 . Hole effect measurements proved that these changes should be attributed to the reduced carrier concentration and enhanced carrier mobility. The comprehensive density functional theory calculations including electron density map analysis for the hypothetical model Ca 4.5 Eu 0.5 Al 2 Sb 6 revealed that the polarity between Al and Sb forming the anionic frameworks decreased as the Eu-dopants were introduced, which eventually affected the carrier mobility in the anionic frameworks. Thermal conductivity measurements proved that the Eu-doping successfully lowered the lattice thermal conductivity because of the enhanced atomic disordering. In conclusion, the magnetization measurements for Ca 4.37(2) Eu 0.63 Al 2 Sb 6 showed a typical Curie–Weiss behavior with weak antiferromagnetic nearest-neighbor interactions with θ p = -5.07 K.

36 MATERIALS SCIENCE↗
NASA NTRS2022

Preliminary Airfoil Design for Low Reynolds Numbers

Advances in the fields of electronics, batteries, and electric motors have enabled broad adoption of small-scale aircraft for various terrestrial applications. Numerous Micro Aerial Vehicles (MAVs) and small Unmanned Aerial Vehicles (UAVs), both civil and military, are in use today. Operation at their design flight condition often requires rotors, propellers, or wings to perform at Reynolds numbers significantly below 500,000 [1]. Airfoil performance at low Reynolds numbers is generally characterized by low aerodynamic performance (i.e. the attainable lift-to-drag ratio) compared to performance of airfoils at higher Reynolds numbers. The critical chord-based Reynolds number for conventional airfoils lies around Rec = 100,000 to Rec = 500,000 [2]. Below this critical Reynolds number, laminar separation of the boundary layer is usually the cause for poor performance. Researchers have found that below the critical Reynolds number, flat and cambered plates can outperform smooth airfoils. Circular-arc cambered plates especially have remarkable performance advantages compared to conventional airfoil shapes [3].

airfoil↗
NASA NTRS2011

NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE)

Nearly 40 years have passed since the last Apollo missions investigated the mysteries of the lunar atmosphere and the question of levitated lunar dust. The most important questions remain: what is the composition, structure and variability of the tenuous lunar exosphere? What are its origins, transport mechanisms, and loss processes? Is lofted lunar dust the cause of the horizon glow observed by the Surveyor missions and Apollo astronauts? How does such levitated dust arise and move, what is its density, and what is its ultimate fate? The US National Academy of Sciences/National Research Council decadal surveys and the recent "Scientific Context for Exploration of the Moon" (SCEM) reports have identified studies of the pristine state of the lunar atmosphere and dust environment as among the leading priorities for future lunar science missions. These measurements have become particularly important since recent observations by the Lunar Crater Observation and Sensing Satellite (LCROSS) mission point to significant amounts of water and other volatiles sequestered within polar lunar cold traps. Moreover Chandrayaan/M3, EPOXI and Cassini/VIMS have identified molecular water and hydroxyl on lunar surface regolith grains. Variability in concentration suggests these species are likely to be present in the exosphere, and thus constitute a source for the cold traps. NASA s Lunar Atmosphere and Dust Environment Explorer (LADEE) is currently under development to address these goals. LADEE will determine the composition of the lunar atmosphere and investigate the processes that control its distribution and variability, including sources, sinks, and surface interactions. LADEE will also determine whether dust is present in the lunar exosphere, and reveal its sources and variability. LADEE s results are relevant to surface boundary exospheres and dust processes throughout the solar system, will address questions regarding the origin and evolution of lunar volatiles, and will have implications for future exploration activities. LADEE will be the first mission based on the Ames Common Bus design. LADEE employs a high heritage instrument payload: a Neutral Mass Spectrometer (NMS), an Ultraviolet/Visible Spectrometer (UVS), and the Lunar Dust Experiment (LDEX). It will also carry a space terminal as part of the Lunar Laser Communication Demonstration (LLCD), which is a technology demonstration. LLCD will also supply a ground terminal. LLCD is funded by the Space Operations Mission Directorate (SOMD), managed by GSFC, and built by MIT Lincoln Lab. NMS was directed to the Goddard Space Flight Center (GSFC) and UVS to Ames Research Center (ARC). LDEX was selected through the Stand Alone Missions of Opportunity Notice (SALMON) Acquisition Process, and is provided by the University of Colorado at Boulder. The LADEE NMS covers a m/z range of 2-150 and draws its design from mass spectrometers developed at GSFC for the MSL/SAM, Cassini Orbiter, CONTOUR, and MAVEN missions. The UVS instrument is a next-generation, high-reliability version of the LCROSS UV-Vis spectrometer, spanning 250-800 nm wavelength, with high (<1 nm) spectral resolution. UVS will also perform dust occultation measurements via a solar viewer optic. LDEX senses dust impacts in situ, at LADEE orbital altitudes of 50 km and below, with a particle size range of between 100 nm and 5 micron. Dust particle impacts on a large hemispherical target create electron and ion pairs. The latter are focused and accelerated in an electric field and detected at a microchannel plate. LADEE is an important part of NASA s portfolio of near-term lunar missions; launch is planned for May, 2013. The lunar atmosphere is the most accessible example of a surface boundary exosphere, and may reveal the sources and cycling of volatiles. Dynamic dust activity must be accounted for in the design and operation of lunar surface operations.

Elphic, Richard↗
NASA NTRS1993

Decay of equatorial ring current ions and associated aeronomical consequences

The decay of the major ion species which constitute the ring current is studied by solving the time evolution of their distribution functions during the recovery phase of a moderate geomagnetic storm. In this work, only equatorially mirroring particles are considered. Particles are assumed to move subject to E x B and gradient drifts. They also experience loses along their drift paths. Two loss mechanisms are considered: charge exchange with neutral hydrogen atoms and Coulomb collisions with thermal plasma in the plasmasphere. Thermal plasma densities are calculated with a plasmaspheric model employing a time-dependent convection electric field model. The drift-loss model successfully reproduces a number of important and observable features in the distribution function. Charge exchange is found to be the major loss mechanism for the ring current ions; however the important effects of Coulomb collisions on both the ring current and thermal populations are also presented. The model predicts the formation of a low-energy (less than 500 eV) ion population as a result of energy degradation caused by Coulomb collision of the ring current ions with the plasmaspheric electrons; this population may be one source of the low-energy ions observed during active and quiet periods in the inner magnetosphere. The energy transferred to plasmaspheric electrons through Coulomb collisions with ring current ions is believed to be the energy source for the electron temperature enhancement and the associated 6300 A (stable auroral red (SAR) arc) emission in the subauroral region. The calculated energy deposition rate is sufficient to produce a subauroral electron temperature enhancement and SAR arc emissions that are consistent with observations of these quantities during moderate magnetic activity levels.

Fok, M.-C.↗