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NASA NTRS2000

Research Activities at Plasma Research Laboratory at NASA Ames Research Center

In order to meet NASA's requirements for the rapid development and validation of future generation electronic devices as well as associated materials and processes, enabling technologies are being developed at NASA-Ames Research Center using a multi-discipline approach. The first step is to understand the basic physics of the chemical reactions in the area of plasma reactors and processes. Low pressure glow discharges are indispensable in the fabrication of microelectronic circuits. These plasmas are used to deposit materials and also etch fine features in device fabrication. However, many plasma-based processes suffer from stability and reliability problems leading to a compromise in performance and a potentially increased cost for the semiconductor manufacturing industry. Although a great deal of laboratory-scale research has been performed on many of these processing plasmas, little is known about the gas-phase and surface chemical reactions that are critical in many etch and deposition processes, and how these reactions are influenced by the variation in operating conditions. Such a lack of understanding has hindered the development of process models that can aid in the scaling and improvement of plasma etch and deposition systems. Our present research involves the study of such plasmas. An inductively-coupled plasma (ICP) source in place of the standard upper electrode assembly of the Gaseous Electronics Conference (GEC) radio-frequency (RF) Reference Cell is used to investigate the discharge characteristics. This ICP source generates plasmas with higher electron densities and lower operating pressures than obtainable with the original parallel-plate version of the GEC Cell. This expanded operating regime is more relevant to new generations of industrial plasma systems being used by the microelectronics industry. The research goal is to develop an understanding of the physical phenomena involved in plasma processing and to measure much needed fundamental parameters, such as gas phase and surface reaction rates, species concentration, temperature, ion energy distribution, and electron number density.

Sharma, S. P.↗

DOE OSTI2024

Towards modelling AR Sco: generalized particle dynamics and strong radiation-reaction regimes

Numerical simulations of relativistic plasmas have become more feasible, popular, and crucial for various astrophysical sources with the availability of computational resources. The necessity for high-accuracy particle dynamics is especially highlighted in pulsar modelling due to the extreme associated electromagnetic fields and particle Lorentz factors. Including the radiation-reaction force in the particle dynamics adds even more complexity to the problem, but is crucial for such extreme astrophysical sources. We have also realized the need for such modelling concerning magnetic mirroring and particle injection models proposed for AR Sco, the first white dwarf pulsar. This paper demonstrates the benefits of using higher-order explicit numerical integrators with adaptive time-step methods to solve the full particle dynamics with radiation-reaction forces included. We show that for standard test scenarios, namely various combinations of uniform E- and B-fields and a static dipole B-field, the schemes we use are equivalent to and in extreme field cases outperform standard symplectic integrators in accuracy. We show that the higher-order schemes have massive computational time improvements due to the adaptive time-steps we implement, especially in non-uniform field scenarios and included radiation reaction where the particle gyro-radius rapidly changes. When balancing accuracy and computational time, we identified the adaptive Dormand–Prince eighth-order scheme to be ideal for our use cases. The schemes we use maintain accuracy and stability in describing the particle dynamics and we indicate how a charged particle enters radiation-reaction equilibrium and conforms to the analytical Aristotelian Electrodynamics expectations.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2022

Preconditioned least‐squares Petrov–Galerkin reduced order models

Abstract In this article, we introduce a methodology for improving the accuracy and efficiency of reduced order models (ROMs) constructed using the least‐squares Petrov–Galerkin (LSPG) projection method through the introduction of preconditioning. Unlike prior related work, which focuses on preconditioning the linear systems arising within the ROM numerical solution procedure to improve linear solver performance, our approach leverages a preconditioning matrix directly within the minimization problem underlying the LSPG formulation. Applying preconditioning in this way has the potential to improve ROM accuracy for several reasons. First, preconditioning the LSPG formulation changes the norm defining the residual minimization, which can improve the residual‐based stability constant bounding the ROM solution's error. The incorporation of a preconditioner into the LSPG formulation can have the additional effect of scaling the components of the residual being minimized to make them roughly of the same magnitude, which can be beneficial when applying the LSPG method to problems with disparate scales (e.g., dimensional equations, multi‐physics problems). Importantly, we demonstrate that an “ideal preconditioned” LSPG ROM (a ROM in which the preconditioner is the inverse of the Jacobian of its corresponding full order model) emulates projection of the full order model solution increment onto the reduced basis. This quantity defines a lower bound on the error of a ROM solution for a given reduced basis. By designing preconditioners that approximate the Jacobian inverse—as is common in designing preconditioners for solving linear systems—it is possible to obtain a ROM whose error approaches this lower bound. The proposed approach is evaluated on several mechanical and thermo‐mechanical problems implemented within the Albany HPC code and run in the predictive regime, with prediction across material parameter space. We demonstrate numerically that the introduction of simple Jacobi, Gauss‐Seidel, and ILU preconditioners into the proper orthogonal decomposition/LSPG formulation reduces significantly the ROM solution error, the reduced Jacobian condition number, the number of nonlinear iterations required to reach convergence, and the wall time (thereby improving efficiency). Moreover, our numerical results reveal that the introduction of preconditioning can deliver a robust and accurate solution for test cases in which the unpreconditioned LSPG method fails to converge.

Lindsay, Payton↗

DOE OSTI2020

Combinatorial Synthesis and High-Throughput Characterization of Microstructure and Phase Transformation in Ni–Ti–Cu–V Quaternary Thin-Film Library

Ni–Ti–based shape memory alloys (SMAs) have found widespread use in the last 70 years, but improving their functional stability remains a key quest for more robust and advanced applications. Named for their ability to retain their processed shape as a result of a reversible martensitic transformation, SMAs are highly sensitive to compositional variations. Alloying with ternary and quaternary elements to fine-tune the lattice parameters and the thermal hysteresis of an SMA, therefore, becomes a challenge in materials exploration. Combinatorial materials science allows streamlining of the synthesis process and data management from multiple characterization techniques. In this study, a composition spread of Ni–Ti–Cu–V thin-film library was synthesized by magnetron co-sputtering on a thermally oxidized Si wafer. Composition-dependent phase transformation temperature and microstructure were investigated and determined using high-throughput wavelength dispersive spectroscopy, synchrotron X-ray diffraction, and temperature-dependent resistance measurements. Of the 177 compositions in the materials library, 32 were observed to have shape memory effect, of which five had zero or near-zero thermal hysteresis. These compositions provide flexibility in the operating temperature regimes that they can be used in. A phase map for the quaternary system and correlations of functional properties are discussed with respect to the local microstructure and composition of the thin-film library.

42 ENGINEERING↗

DOE OSTI2022

Stability of Fe 2 S and Fe 12 S 7 to 125 GPa; implications for S-rich planetary cores

The Fe-FeS phase relations were explored in the 22–25 wt. % S compositional range using single crystal X-ray diffraction in a laser heated diamond anvil cell. At pressures up to 125 GPa and at high temperatures, Fe 2 S and Fe 12 S 7 were determined to co-crystallise. The novel Fe 12 S 7 compound adopts the Co 12 P 7 structure and Fe 2 S assumes the Fe 2 P-type structure. Applying these results to an Fe-FeS binary phase diagram exposes a complex series of FeS phase assemblages in the 16–25 wt. % S range, whereby minor changes in S content significantly affect the crystallisation sequence of Fe-S rich planetary cores. For core compositions S-rich of the Fe 2 S-Fe 12 S 7 eutectic, the small density difference between solid Fe 12 S 7 and Fe 2 S is likely to result in the formation of a core slush rather than a gravitationally stable inner core. Crystallisation of denser Fe 2 S at eutectic conditions could then result in gravitational settling of an Fe 2 S-rich inner core over time. As the Fe 2 P-type Fe 2 S has previously been identified forming at high temperatures to pressures as low as 22 GPa, the core crystallisation regimes determined here also elucidate that the Martian core sulfur composition must lie on the S-rich side of the Fe-Fe 3 S eutectic or even the S-rich side of the Fe 3 S-Fe 2 S eutectic to maintain a fully molten core.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Phase segregation and miscibility of TiO x nanocomposites in Gd-doped ceria solid electrolyte material

Electro-chemo-mechanical (ECM) coupling refers to mechanical deformation due to electrochemically driven compositional change in a solid. An ECM actuator producing micrometre-size displacements and long-term stability at room temperature was recently reported, comprising a 20 mol% Gd-doped ceria (20GDC), a solid electrolyte membrane, placed between two working bodies made of TiO x /20GDC (Ti-GDC) nanocomposites with Ti concentration of 38 mol%. The volumetric changes originating from oxidation or reduction in the local TiO x units are hypothesized to be the origin of mechanical deformation in the ECM actuator. Studying the Ti concentration-dependent structural changes in the Ti-GDC nanocomposites is therefore required for (i) understanding the mechanism of dimensional changes in the ECM actuator and (ii) maximizing the ECM response. Here, the systematic investigation of the local structure of the Ti and Ce ions in Ti-GDC over a broad range of Ti concentrations using synchrotron X-ray absorption spectroscopy and X-ray diffraction is reported. The main finding is that, depending on the Ti concentration, Ti atoms either form a cerium titanate or segregate into a TiO 2 anatase-like phase. The transition region between these two regimes with Ti(IV) concentration between 19% and 57% contained strongly disordered TiO x units dispersed in 20GDC containing Ce(III) and Ce(IV) and hence rich with oxygen vacancies. As a result, this transition region is proposed to be the most advantageous for developing ECM-active materials.

47 OTHER INSTRUMENTATION↗

NASA NTRS1995

Kinetic structure of intermediate shocks: Implications for the magnetopause

A general study of the structure and stability of intermediate shocks (IS) in an isotropic plasma is presented using a hybrid as well as a resistive Hall MHD code. Special emphasis is put on the question of whether the rotational layers observed at the magnetopause can be intermediate shocks. The shocks are formed dynamically by the interaction between a flowing plasma and a stationary piston. Coplanar ISs (both strong and weak) are found to be stable in a collisionless plasma. The existence of slow shocks in a high beta plasma is also established for the first time. Noncoplanar ISs are found to be time-dependent, evolving toward a rotational discontinuity (RD) after some characteristic time tau which can be quite long (1000 Omega(exp -1), where Omega is the ion gyrofrequency). The value tau is larger the closer the rotation angle is to 180 deg. Rotations larger than 180 deg are found to be unstable, decaying into a state of minimum shear (i.e., rotation angle less than 180 deg). There are various length scales associated with an IS in the kinetic regime. The shortest scale is found to be the length scale over which rotation of the transverse component of the magnetic field takes place. This scale can have a half width as small as one ion inertial length (c/omega(sub p)) for electron sense rotations and 3c/omega(sub p) for ion sense rotations, for an upstream ion beta of unity. Both of these scales are consistent with the observed thickness at the magnetopause and identical to the corresponding RD scales. A detailed study of the mode conversion of the Alfven ion cyclotron waves (A/IC) waves across both slow and intermediate shocks and the resulting downstream wave spectrum are presented. The possibility that the large number of relfected ions observed at the magnetopause may be due to the presence of strong ISs is considered. The identification of strong ISs and their distinction from RDs should be possible in observations due to significant differences that exist between jump conditions and overall structure of the two discontinuities. The jumps in the plasma parameters across a weak IS are typically small. This together with the fact that the weak ISs and RDs have very similar thickness and other overall properties makes the distinction between weak ISs and RDs in the observations largely inconsequential. However, at large noncoplanarity angles the weak IS approaches the RD limit in a relatively short time (approximately less than 100 Omega (exp -1)). Thus, magnetopause rotations with large noncoplanarity angles are most likely either RDs or strong ISs. Finally, direct comparisons between fluid (resistive Hall MHD) and kinetic simulations show that fluid theory is not applicable to study of ISs in a collisionless plasma.

Karimabadi, H.↗

NASA NTRS2010

Methods and Results for a Global Precipitation Measurement (GPM) Validation Network Prototype

As one component of a ground validation system to meet requirements for the upcoming Global Precipitation Measurement (GPM) mission, a quasi-operational prototype a system to compare satellite- and ground-based radar measurements has been developed. This prototype, the GPM Validation Network (VN), acquires data from the Precipitation Radar (PR) on the Tropical Rainfall Measuring Mission (TRMM) satellite and from ground radar (GR) networks in the continental U.S. and participating international sites. PR data serve as a surrogate for similar observations from the Dual-frequency Precipitation Radar (DPR) to be present on GPM. Primary goals of the VN prototype are to understand and characterize the variability and bias of precipitation retrievals between the PR and GR in various precipitation regimes at large scales, and to improve precipitation retrieval algorithms for the GPM instruments. The current VN capabilities concentrate on comparisons of the base reflectivity observations between the PR and GR, and include support for rain rate comparisons. The VN algorithm resamples PR and GR reflectivity and other 2-D and 3-D data fields to irregular common volumes defined by the geometric intersection of the instrument observations, and performs statistical comparisons of PR and GR reflectivity and estimated rain rates. Algorithmic biases and uncertainties introduced by traditional data analysis techniques are minimized by not performing interpolation or extrapolation of data to a fixed grid. The core VN dataset consists of WSR-88D GR data and matching PR orbit subset data covering 21 sites in the southeastern U. S., from August, 2006 to the present. On average, about 3.5 overpass events per month for these WSR-88D sites meet VN criteria for significant precipitation, and have matching PR and GR data available. This large statistical sample has allowed the relative calibration accuracy and stability of the individual ground radars, and the quality of the PR reflectivity attenuation correction in convective and stratiform precipitation to be evaluated. We will present results of PR-GR reflectivity and rain rate bias comparisons for each OR site, and for different rain types, for the full data set and as time series. The capabilities of the statistical analysis and vertical cross section tools for display and analysis of individual site overpass event data will be described, and examples of the tools' outputs will be shown.

Morris, Kenneth R.↗

NASA NTRS2002

An Experimental Investigation of Incompressible Richtmyer-Meshkov Instability

Richtmyer-Meshkov (RM) instability occurs when two different density fluids are impulsively accelerated in the direction normal to their nearly planar interface. The instability causes small perturbations on the interface to grow and eventually become a turbulent flow. It is closely related to Rayleigh-Taylor instability, which is the instability of a planar interface undergoing constant acceleration, such as caused by the suspension of a heavy fluid over a lighter one in the earth's gravitational field. Like the well-known Kelvin-Helmholtz instability, RM instability is a fundamental hydrodynamic instability which exhibits many of the nonlinear complexities that transform simple initial conditions into a complex turbulent flow. Furthermore, the simplicity of RM instability (in that it requires very few defining parameters), and the fact that it can be generated in a closed container, makes it an excellent test bed to study nonlinear stability theory as well as turbulent transport in a heterogeneous system. However, the fact that RM instability involves fluids of unequal densities which experience negligible gravitational force, except during the impulsive acceleration, requires RM instability experiments to be carried out under conditions of microgravity. This experimental study investigates the instability of an interface between incompressible, miscible liquids with an initial sinusoidal perturbation. The impulsive acceleration is generated by bouncing a rectangular tank containing two different density liquids off a retractable vertical spring. The initial perturbation is produced prior to release by oscillating the tank in the horizontal direction to produce a standing wave. The instability evolves in microgravity as the tank travels up and then down the vertical rails of a drop tower until hitting a shock absorber at the bottom. Planar Laser Induced Fluorescence (PLIF) is employed to visualize the flow. PLIF images are captured by a video camera that travels with the tank. Figure 1 is as sequence of images showing the development of the instability from the initial sinusoidal disturbance far into the nonlinear regime which is characterized by the appearance of mushroom structures resulting from the coalescence of baroclinic vorticity produced by the impulsive acceleration. At later times in this sequence the vortex cores are observed to become unstable showing the beginnings of the transition to turbulence in this flow. The amplitude of the growing disturbance after the impulsive acceleration is measured and found to agree well with theoretical predictions. The effects of Reynolds number (based on circulation) on the development of the vortices and the transition to turbulence are also determined.

Jacobs, J. W.↗

DOE OSTI2020

PbS/CdS Quantum Dot Room-Temperature Single-Emitter Spectroscopy Reaches the Telecom O and S Bands via an Engineered Stability

We synthesized PbS/CdS core/shell quantum dots (QDs) to have functional single-emitter properties for room-temperature, solid-state operation in the telecom O and S bands. Two shell-growth methods–cation exchange and successive ionic layer adsorption and reaction (SILAR)–were employed to prepare QD heterostructures with shells of 2–16 monolayers. PbS/CdS QDs were sufficiently bright and stable to resolve photoluminescence (PL) spectra representing both bands from single nanocrystals using standard detection methods, and for a QD emitting in the O-band a second-order correlation function showed strong photon antibunching, important steps toward demonstrating the utility of lead chalcogenide QDs as single-photon emitters (SPEs). Irrespective of type, few telecom-SPEs exist that are capable of such room-temperature operation. Access to single-QD spectra enabled a direct assessment of spectral line width, which was ~70–90 meV compared to much broader ensemble spectra (~300 meV). We show inhomogeneous broadening results from dispersity in PbS core sizes that increases dramatically with extended cation exchange. Quantum yields (QYs) are negatively impacted at thick shells (>6 monolayers) and, especially, by SILAR-growth conditions. Time-resolved PL measurements revealed that, with SILAR, initially single-exponential PL-decays transition to biexponential, with opening of nonradiative carrier-recombination channels. Radiative decay times are, overall, longer for core/shell QDs compared to PbS cores, which we demonstrate can be partially attributed to some core/shell sizes occupying a quasi-type II electron–hole localization regime. Finally, we demonstrate that shell engineering and the use of lower laser-excitation powers can afford significantly suppressed blinking and photobleaching. However, dependence on shell thickness comes at a cost of less-than-optimal brightness, with implications for both materials and experimental design

36 MATERIALS SCIENCE↗

DOE OSTI2025

High-compression implosions based on high density carbon ablator using modified drive and capsule dopant profiles

Laser-driven inertial fusion experiments have, for the first time, achieved a target gain greater than unity in a laboratory setting [Abu-Shawareb et al., Phys. Rev. Lett. 132, 065102 (2024)]. Despite this breakthrough, the burn-up fraction remains limited to about one-fourth of ideal estimates due to insufficient areal density, highlighting the potential for greater gains through enhanced compression. In our previous work, we demonstrated record-high compression of stagnated fuel in indirectly driven implosions using high-density carbon ablators. This was achieved by combining a continuous ramped pulse drive with a modified ablator dopant profile, which reduced mixing at the fuel–ablator interface and improved stability [Tommasini et al., Phys. Rev. Res. 5, L042034 (2023)]. Based on this foundation, the study presented here investigates the limits of compression achievable by combining the continuous ramped pulse drive with different dopant profiles to further minimize unstable interfaces and gradient discontinuities, thereby reducing fuel–ablator mixing. Our results demonstrate that the continuous ramped pulse consistently outperforms designs based on 3-shock drive pulses across all ablator profiles studied, with compression showing only a relatively modest dependence on dopant configurations that reduce the number of interfaces or eliminate discontinuities in the dopant gradient profile. Sub-scale experiments using the continuous ramped pulse achieved compression levels exceeding those of full-scale “HyE” implosions [Kritcher et al., Phys. Plasmas 28, 072706 (2021)] at similar adiabat, anticipating significant performance gains with increased scale, as supported by models and simulations. These findings underscore the critical role of the continuous ramped pulse in reducing mix and achieving improved compression. They also provide a foundation for future large-scale experiments to test the continuous ramped pulse design on deuterium–tritium fuel in the burn-wave propagation regime, leveraging the most effective combinations of continuous ramped pulse and dopant profiles identified in this study.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1987

A comparative study of rapidly and slowly rotating dynamical regimes in a terrestrial general circulation model

As a preliminary step in the development of a general circulation model for general planetary use, a simplified vesion of thef GISS Model I GCM has been run at various rotation periods to investigate differences between the dynamical regimes of rapidly and slowly rotating planets. To isolate the dynamical processes, the hydrologic cycle is suppressed and the atmosphere is forced with perpetual annual mean solar heating. All other parameters except the rotation period remain fixed at their terrestrial values. Experiments were conducted for rotation periods of 2/3, 1, 2, 4, 8, 16, 64 and 256 days. The results are in qualitative agreement with similar experiments carried out previously with other GCMs and with certain aspects of one Venus GCM simulation. As rotation rate decreases, the energetics shifts from baroclinc to quasi-barotropic when the Rossby radius of deformation reaches planetary scale. The Hadley cell expands poleward and replaces eddies as the primary mode of large-scale heat transport. Associated with this is a poleward shift of the baroclinic zone and jet stream and a reduction of the equator-pole temperature contrast. Midlatitude jet strength peaks at 8 days period, as does the weak positive equatorial zonal wind which occurs at upper levels at all rotation periods. Eddy momentum transport switches from poleward to equatorward at the same period. Tropospheric mean static stability generally increases in the tropics and decreases in midlatitudes as rotation rate decreases, but the global mean static stability is independent of rotation rate. The peak in the eddy kinetic energy spectrum shifts toward lower wavenumbers, reaching wavenumber 1 at a period of 8 days. Implications of these results for the dynamics of Venus and Titan are discussed. Specifically, it is suggested that the extent of low-level convection determines whether the Gierasch mechanism contributes significantly to equatorial superrotation on these planets.

Del Genio, Anthony D.↗

DOE OSTI2021

Bulk nanocrystalline Al alloys with hierarchical reinforcement structures via grain boundary segregation and complexion formation

Grain size engineering, particularly reducing grain size into the nanocrystalline regime, offers a promising pathway to further improve the strength-to-weight ratio of Al alloys. Unfortunately, the fabrication of nanocrystalline metals often requires non-equilibrium processing routes, which typically limit the specimen size and require large energy budgets. In this study, multiple dopant elements in ternary Al alloys are deliberately selected to enable segregation to the grain boundary region and promote the formation of amorphous complexions. Three different fully dense bulk nanocrystalline Al alloys (Al-Mg-Y, Al-Fe-Y, and Al-Ni-Y) with small grain sizes were successfully fabricated using a simple powder metallurgy approach, with full densification connected directly to the onset of amorphous complexion formation. All the compositions demonstrate densities above 99% with grain sizes <60 nm following consolidation via hot pressing at 585 °C. The very fine grain structure results in excellent mechanical properties, as evidenced by nanoindentation hardness values in the range of 2.2-2.8 GPa. Detailed microstructural characterization verifies the segregation of all dopant species to grain boundaries as well as the formation of amorphous complexions, which suggests their influential role in aiding effective consolidation and endowing thermal stability in the alloys. Moreover, nanorods with a core-shell structure are also observed at the grain boundaries, which likely contribute to the stabilization of the grain structure while also strengthening the materials. Lastly, intermetallic particles with sizes of hundreds of nanometers form in all systems. As a whole, the results presented here demonstrate a general alloy design strategy of segregation and boundary evolution pathway that enables the fabrication of multiple nanocrystalline Al alloys with hierarchical microstructures and improved performance.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Addressing R D() , R K() , muon g -2 and ANITA anomalies in a minimal R-parity violating supersymmetric framework

We analyze the recent hints of lepton flavor universality violation in both charged-current and neutral-current rare decays of B mesons in an R -parity-violating supersymmetric scenario. Motivated by simplicity and minimality, we had earlier postulated the third-generation superpartners to be the lightest (calling the scenario “RPV3”) and explicitly showed that it preserves gauge coupling unification and of course has the usual attribute of naturally addressing the Higgs radiative stability. Here we show that both R D ( * ) and R K ( * ) flavor anomalies can be addressed in this RPV3 framework. Interestingly, this scenario may also be able to accommodate two other seemingly disparate anomalies, namely, the longstanding discrepancy in the muon ( g - 2 ), as well as the recent anomalous upgoing ultrahigh-energy Antarctic Impulsive Transient Antenna events. Based on symmetry arguments, we consider three different benchmark points for the relevant RPV3 couplings and carve out the regions of parameter space where all (or some) of these anomalies can be simultaneously explained. We find it remarkable that such overlap regions exist, given the plethora of precision low-energy and high-energy experimental constraints on the minimal model parameter space. The third-generation superpartners needed in this theoretical construction are all in the 1–10 TeV range, accessible at the LHC and/or next-generation hadron colliders. We also discuss some testable predictions for the lepton-flavor-violating decays of the tau lepton and B mesons for the current and future B -physics experiments, such as LHCb and Belle II. Complementary tests of the flavor anomalies in the high- p T regime in collider experiments such as the LHC are also discussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS2009

ARTEMIS: The First Mission to the Lunar Libration Orbits

The ARTEMIS mission will be the first to navigate to and perform stationkeeping operations around the Earth-Moon L1 and L2 Lagrangian points. The NASA Goddard Space Flight Center (GSFC) has previous mission experience flying in the Sun-Earth L1 (SOHO, ACE, WIND, ISEE-3) and L2 regimes (WMAP) and have maintained these spacecraft in libration point orbits by performing regular orbit stationkeeping maneuvers. The ARTEMIS mission will build on these experiences, but stationkeeping in Earth-Moon libration orbits presents new challenges since the libration point orbit period is on the order of two weeks rather than six months. As a result, stationkeeping maneuvers to maintain the Lissajous orbit will need to be performed frequently, and the orbit determination solutions between maneuvers will need to be quite accurate. The ARTEMIS mission is a collaborative effort between NASA GSFC, the University of California at Berkeley (UCB), and the Jet Propulsion Laboratory (JPL). The ARTEMIS mission is part of the THEMIS extended mission. ARTEMIS comprises two of the five THEMIS spacecraft that will be maneuvered from near-Earth orbits into lunar libration orbits using a sequence of designed orbital maneuvers and Moon & Earth gravity assists. In July 2009, a series of orbit-raising maneuvers began the proper orbit phasing of the two spacecraft for the first lunar flybys. Over subsequent months, additional propulsive maneuvers and gravity assists will be performed to move each spacecraft though the Sun-Earth weak stability regions and eventually into Earth-Moon libration point orbits. We will present the overall orbit designs for the two ARTEMIS spacecraft and provide analysis results of the 3/4-body dynamics, and the sensitivities of the trajectory design to both · maneuver errors and orbit determination errors. We will present results from the. initial orbit-raising maneuvers.

Woodward, Mark↗

NASA NTRSDate not supplied

A Robust Uniform Control Approach for VTOL Aircraft

We present a uniform control approach for transitioning vertical take-off and landing aircraft. The approach combines several well-understood linear techniques, including robust servomechanism linear quadratic regulation, control allocation, and gain scheduling, to provide a practical control framework that can be used to unify the control design process in all flight regimes. The choice of command variables provides a pilot/operator with a uniform set of intuitive control inputs through all phases of flight while also being easily integrated into autonomous trajectory tracking operations. The control method is applied to the NASA LA-8 aircraft, a tandem tiltwing distributed electric propulsion research vehicle designed at NASA Langley Research Center. The trim envelope of the aircraft is explored and the aircraft control authority analyzed throughout the transition corridor. The uniform control approach is then used to develop reference command tracking controllers for both the longitudinal and lateral-directional dynamics. An example trajectory is simulated to demonstrate how the controller effectively transitions the aircraft from hover to forward flight and vice versa while tracking a desired trajectory.

VTOL↗

NASA NTRS2019

Long Term Biological Treatment of Space Habitation Waste Waters in a One Stage MABR: Comparison of Operation for N and C Oxidation With and Without Simultaneous Denitrification

Aerobic biological stabilization has been previously demonstrated for full size MABR?s (CoMANDR 1.0, CoMANDR 2.0, and R-CoMANDR) over operating periods of ~1 year. These systems have successfully treated a variety of possible habitation waste streams including an ISS (urine + flush and humidity condensate) and Early Planetary Base (EPB) wastewater (urine, flush water, hygiene wastewater, and laundry). Biological stabilization has a number of advantages including: 1) elimination of hazardous pre-treat chemicals; 2) production of NOx species (that can be easily rejected by evaporative or membrane systems); 3) elimination of volatile organic constituents; 4) a low pH effluent that facilitates membrane and distillation processes; and 5) a effluent that produces a better quality and less hazardous brine for water recovery. Previous work has primarily evaluated aerobic operation in which organic carbon and nitrogen is converted to CO2 and NOx-, respectively. An alternative to aerobic operation would be to include anoxic operation to promote denitrification and production of N2 gas. This allows for production of make-up gas as well as reduces the O2 demand and can increase ammonia oxidation efficiency. We evaluated the operation of a full scale (2 crew/day) MABR operated to perform oxidation of organic carbon and nitrogen with and without simultaneous reduction of oxidized N to N2 gas, simultaneous nitrification denitrification (SNDN). The system was challenged with a variety of space habitation wastewaters ranging from an ISS composition to a possible EPB waste stream under both continuous and on-production feeding modes. The system has been operated for over 2.5 years. We report on an overall comparison of aerobic oxidation and SNDN operational regimes to evaluate the system with the best overall attributes to support recycling of space habitation waste streams.

Biological water processing↗

DOE OSTI2021

Theoretical analysis of the saturation phase of the 1/1 energetic-ion-driven resistive interchange mode

The aim of the present study is to analyze the saturation regime of the energetic-ion-driven resistive interchange mode (EIC) in the LHD plasma. In this work, a set of nonlinear simulations are performed by the FAR3d code that uses a reduced MHD model for the thermal plasma coupled with a gyrofluid model for the energetic particle (EP) species. The hellically trapped EP component is introduced through a modification of the averaged drift velocity operator to include their precessional drift. The nonlinear simulation results show similar 1/1 EIC saturation phases with respect to the experimental observations, reproducing the enhancement of the n/m = 1/1 resistive interchange modes (RIC) amplitude and width as the EP β increases, the EP β threshold for the 1/1 EIC excitation, the further destabilization of the 1/1 EIC as the population of the helically trapped EP increases and the triggering of burst events. The frequency of the 1/1 EIC calculated during the burst event is 9.4 kHz and the 2/2 and 3/3 overtones are destabilized, consistent with the frequency range and the complex mode structure measured in the experiment. In addition, the simulation shows the inward propagation of the 1/1 EIC due to the nonlinear destabilization of the 3/4 and 2/3 energetic particle modes, leading to the partial overlapping between resonances during the burst event. Finally, the analysis of the 1/1 EIC stabilization phase shows the excitation of the 1/1 RIC as soon as the flattening induced by the 1/1 EIC in the pressure profile vanishes, leading to the retrieval of the pressure gradient at the plasma periphery and the overcoming of the RIC stability limit.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗