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At least 127 records · Page 7

Tri-Agency Reliability Engineering Guidance: Post Mission Disposal and Extension Assessment

The Trilateral partners — the European Space Agency (ESA), Japan Aerospace Exploration Agency (JAXA), and National Aeronautics and Space Administration (NASA) and the United States Government (USG) in their execution of safe and successful missions, have a long-standing history of sustaining the shared space environment of operational Earth-Moon orbits with their global space-stewardship, or spacekeeping, of these areas. This has driven missions to limit the generation of new and long-lived debris, control debris releases, minimize accidental explosions and collisions, and ensure Post-Mission Disposal of space systems, so that the environment remains safe for future operations and explorations. Given the continued need for space systems to support global mandatory infrastructure and commercial enterprise, spacefarers are extending beyond the Trilateral partners, more and smaller satellites are being deployed, and current assets are being utilized much longer than expected. This is making space more congested than ever; therefore, the Trilateral partners are evaluating potential future debris mitigation strategies, evolving technology, developing on-orbit servicing capabilities, and advancing their abilities to assess disposal and mission extension plans. They are also sharing their lessons learned and identifying opportunities for future state-of-the-art advancements for current and future space enterprises. Sustaining the space environment cannot be ensured by any one agency or country. Thus, the Trilateral authors have shared their lessons learned, insights, and guidance, herein, on disposal and mission extension assessment strategies with the gratitude of each agency. As such, this document is not prescriptive, but was formulated to enhance value-and-risk-balanced operational decision-making, support policy refinement, and guide spacefaring partners beyond these agencies to assess their activities in space with safety and a global space-stewardship, or spacekeeping, in mind. This includes not only the disposal and mission extension assessment addressed herein, but also preserving space history, ensuring collaboration/interoperability of technology, supporting fellow operators without interfering, and the utilization of in-situ resources for the common benefit of humankind. It is the intention of the Trilateral partners that this document evolves based on community lessons learned and the introduction of new assessment methodologies. So, all readers are encouraged to share their insights with the authors from their own application of this guidance or other strategies to ensure each mission has a successful, safe, and judicious life and conclusion.

ESA↗

[Clinical and physiological evaluation of bone changes among astronauts after long-term space flights]

Results of the joint Russian/US studies of the effect of microgravity on bone tissues in 18 cosmonauts on return from 4.5- to 14.5-month long missions are presented. Dual-energy x-ray gamma-absorbtiometry (QDR-1000 W, Hologic, USA) was used to measure bone mineral density (BMD, g/cm2) and mineral content (BMC, g) in the whole body, the scalp including cervical vertebra, arms, ribs, sternal and lumbar regions of the spinal column, pelvis and legs. A clearly defined dependence of topography of changes upon the position of a skeletal segment in the gravity vector was established. The greatest BMD losses have been observed in the skeleton of the lower body, i.e. in pelvic bones (-11.99 +/- 1.22%), lumbar vertebra (-5.63 +/- 0.817%), and in proximal femur, particularly in the femoral neck (-8.17 +/- 1.24%). Bones of the upper skeleton were either unchanged (insignificant) or showed a positive trend. Overall changes in bone mass of the whole skeleton of male cosmonauts during the period of about 6 months on mission made up -1.41 +/- 0.406% and suggest the mean balance of calcium over flight equal to -227 +/- 62.8 mg/day. Reasoning is given to qualify these states of cosmonauts' bone tissues as local osteopenia. On the literature and results of authors' clinical evidence, discussed is availability of the densitometric data for predicting risk of trauma. A biological nature of the changes under observation is hypothesized.

NASA Discipline Musculoskeletal↗

Category B Plastic Pane Testing for JSC 66320 Rev A Requirements Verifiable Through Acceptance Testing

JSC 66320, Revision A, Optical Property Requirements for Glasses, Ceramics, and Plastics in Spacecraft Window Systems, lists several quantitative requirements that spacecraft windowpanes must meet. Recently, we were asked to establish a capability at the Kennedy Space Center to perform these measurements on category B plastic panes, i.e., plastic panes that could be used on a spacecraft for long-focal-length photography and piloting. Two of the criteria, normal wavefront and 30-degree wavefront attributes, can be measured with existing equipment and processes (see NASA TM NESC-RP-14-00951, April 2016) and are not discussed in this document. However, the other six criteria-haze, wedge angle, birefringence, reflectance, transmittance, and color balance-required substantial development and are the subject of this document. In this document, we do not discuss the rationale behind the requirements, but we did engage in discussions with the authors of JSC 66320 in order to better understand the requirements and the verifications being imposed on windows and their testing. Accordingly, this document presents our best understanding of the requested requirements and verifications. We also present our methodology for performing each of the six measurements, along with applicable mathematics and a description, with photos, of the hardware used. In addition, we supply the results of a test on a low-quality in-house plastic window as an example of the system operation. Only requirements that can be met by acceptance test and analysis, as opposed to optical inspection, are considered in this document.

spaceflight windows↗

Plasma and field observation of the structures in the polar solar wind

Since passing essentially continuously into regions of solar wind from the southern polar coronal hole at approximately 36 deg S, Ulysses has observed frequent structures lasting from several hours to several days. In addition to Alfven waves and coronal mass ejections, which have been discussed by previous authors, two other sorts of structures are routinely evident. This paper provides the first report of these structures in the high latitude solar wind: (1) small scale compressional structures, and (2) pressure balance structures. The compressional structures are driven by faster solar wind overtaking the slower solar wind ahead of it and exhibit the plasma and field properties expected for compressions. However, unlike large scale stream interaction regions observed in and near the ecliptic plane, these structures are much smaller scale and are transient, not recurring from one rotation to the next. The pressure balance structures are indicated by roughly equal increases in the plasma pressure and decreases in the magnetic field pressure. These structures, which are several degrees across, are more dense and have higher plasma pressures and betas than the surrounding solar wind. These pressure balance structures seem to be likely manifestations of 'polar plumes.'

McComas, D. J.↗

Leveraging Independent Management and Chief Engineer Hierarchy: Vertically and Horizontally-Derived Technical Authority Value

In the development of complex spacecraft missions, project management authority is usually extended hierarchically from NASA's highest agency levels down to the implementing institution's project team level, through both the center and the program. In parallel with management authority, NASA utilizes a complementary, but independent, hierarchy of technical authority (TA) that extends from the agency level to the project, again, through both the center and the program. The chief engineers (CEs) who serve in this technical authority capacity oversee and report on the technical status and ensure sound engineering practices, controls, and management of the projects and programs. At the lowest level, implementing institutions assign project CEs to technically engage projects, lead development teams, and ensure sound technical principles, processes, and issue resolution. At the middle level, programs and centers independently use CEs to ensure the technical success of their projects and programs. At the agency level, NASA's mission directorate CEs maintain technical cognizance over every program and project in their directorate and advise directorate management on the technical, cost, schedule, and programmatic health of each. As part of this vertically-extended CE team, a program level CE manages a continually varying balance between penetration depth and breadth across his or her assigned missions. Teamwork issues and information integration become critical for management at all levels to ensure value-added use of both the synergy available between CEs at the various agency levels, and the independence of the technical authority at each organization.

Barley, Bryan↗

Design of a powered elevator control system

The design, fabrication and flight testing of a powered elevator system for the Augmentor Wing Jet STOL Research Aircraft (AWJSRA or Mod C-8A) are discussed. The system replaces a manual spring tab elevator control system that was unsatisfactory in the STOL flight regime. Pitch control in the AWJSRA is by means of a single elevator control surface. The elevator is used for both maneuver and trim control as the stabilizer is fixed. A fully powered, irreversible flight control system powered by dual hydraulic sources was designed. The existing control columns and single mechanical cable system of the AWJSRA have been retained as has been the basic elevator surface, except that the elevator spring tab is modified into a geared balance tab. The control surface is directly actuated by a dual tandem moving body actuator. Control signals are transmitted from the elevator aft quadrant to the actuator by a linkage system that includes a limited authority series servo actuator.

Glende, W. L. B.↗

Evaluate ERTS imagery for mapping and detection of changes of snowcover on land and on glaciers

The author has identified the following significant results. A possibly more accurate method to determine snowcover area change has been tried; snowcover area change over periods of an ERTS-1 cycle are very useful in determining energy balances over regional areas and to determine snow depth as a function of altitude. Also since shadow and cloud cover areas are highlighted this method may be a step toward more complete machine processing.

Meier, M. F.↗

Break-up characteristics of Chena River Basin

The author has identified the following significant results. Results from snowmelt model were obtained showing the decreasing changes in snow depth for four elevational ranges in the Chena River Basin. This model is based on the energy balance of the snowpack and the results are shown on attached figures. Also, the measured hydrographs for two stations on the Chena River are shown. The next phase of the study will be to analyze the model using both ERTS-1 imagery and measured field values.

Carlson, R. F.↗

Microgravity Two-Phase Flow Transition

Two-phase flows under microgravity condition find a large number of important applications in fluid handling and storage, and spacecraft thermal management. Specifically, under microgravity condition heat transfer between heat exchanger surfaces and fluids depend critically on the distribution and interaction between different fluid phases which are often qualitatively different from the gravity-based systems. Heat transfer and flow analysis in two-phase flows under these conditions require a clear understanding of the flow pattern transition and development of appropriate dimensionless scales for its modeling and prediction. The physics of this flow is however very complex and remains poorly understood. This has led to various inadequacies in flow and heat transfer modeling and has made prediction of flow transition difficult in engineering design of efficient thermal and flow systems. In the present study the available published data for flow transition under microgravity condition are considered for mapping. The transition from slug to annular flow and from bubbly to slug flow are mapped using dimensionless variable combination developed in a previous study by the authors. The result indicate that the new maps describe the flow transitions reasonably well over the range of the data available. The transition maps are examined and the results are discussed in relation to the presumed balance of forces and flow dynamics. It is suggested that further evaluation of the proposed flow and transition mapping will require a wider range of microgravity data expected to be made available in future studies.

Parang, M.↗

Direct Energy Conversion for Low Specific Mass In-Space Power and Propulsion

"Changing the game" in space exploration involves changing the paradigm for the human exploration of the Solar System, e.g, changing the human exploration of Mars from a three-year epic event to an annual expedition. For the purposes of this assessment an "annual expedition" capability is defined as an in-space power & propulsion system which, with launch mass limits as defined in NASA s Mars Architecture 5.0, enables sending a crew to Mars and returning them after a 30-day surface stay within one year, irrespective of planetary alignment. In this work the authors intend to show that obtaining this capability requires the development of an in-space power & propulsion system with an end-to-end specific mass considerably less than 3 kg/kWe. A first order energy balance analysis reveals that the technologies required to create a system with this specific mass include direct energy conversion and nuclear sources that release energy in the form of charged particle beams. This paper lays out this first order approximation and details these conclusions.

Scott, John H.↗

The Global Character of the Flux of Downward Longwave Radiation

Four different types of estimates of the surface downwelling longwave radiative flux (DLR) are reviewed. One group of estimates synthesizes global cloud, aerosol, and other information in a radiation model that is used to calculate fluxes. Because these synthesis fluxes have been assessed against observations, the global-mean values of these fluxes are deemed to be the most credible of the four different categories reviewed. The global, annual mean DLR lies between approximately 344 and 350 W/sq m with an error of approximately +/-10 W/sq m that arises mostly from the uncertainty in atmospheric state that governs the estimation of the clear-sky emission. The authors conclude that the DLR derived from global climate models are biased low by approximately 10 W/sq m and even larger differences are found with respect to reanalysis climate data. The DLR inferred from a surface energy balance closure is also substantially smaller that the range found from synthesis products suggesting that current depictions of surface energy balance also require revision. The effect of clouds on the DLR, largely facilitated by the new cloud base information from the CloudSat radar, is estimated to lie in the range from 24 to 34 W/sq m for the global cloud radiative effect (all-sky minus clear-sky DLR). This effect is strongly modulated by the underlying water vapor that gives rise to a maximum sensitivity of the DLR to cloud occurring in the colder drier regions of the planet. The bottom of atmosphere (BOA) cloud effect directly contrast the effect of clouds on the top of atmosphere (TOA) fluxes that is maximum in regions of deepest and coldest clouds in the moist tropics.

Stephens, Graeme L.↗

The role of ETG modes in JET–ILW pedestals with varying levels of power and fuelling

Abstract We present the results of GENE gyrokinetic calculations based on a series of JET–ITER-like-wall (ILW) type I ELMy H-mode discharges operating with similar experimental inputs but at different levels of power and gas fuelling. We show that turbulence due to electron-temperature-gradient (ETGs) modes produces a significant amount of heat flux in four JET–ILW discharges, and, when combined with neoclassical simulations, is able to reproduce the experimental heat flux for the two low gas pulses. The simulations plausibly reproduce the high-gas heat fluxes as well, although power balance analysis is complicated by short ELM cycles. By independently varying the normalised temperature gradients ( ω T e ) and normalised density gradients ( ω n e ) around their experimental values, we demonstrate that it is the ratio of these two quantities η e = ω T e / ω n e that determines the location of the peak in the ETG growth rate and heat flux spectra. The heat flux increases rapidly as η e increases above the experimental point, suggesting that ETGs limit the temperature gradient in these pulses. When quantities are normalised using the minor radius, only increases in ω T e produce appreciable increases in the ETG growth rates, as well as the largest increases in turbulent heat flux which follow scalings similar to that of critical balance theory. However, when the heat flux is normalised to the electron gyro-Bohm heat flux using the temperature gradient scale length L T e , it follows a linear trend in correspondence with previous work by different authors.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

Mission Assurance Modeling and Simulation: A Cyber Security Roadmap

This paper proposes a cyber security modeling and simulation roadmap to enhance mission assurance governance and establish risk reduction processes within constrained budgets. The term mission assurance stems from risk management work by Carnegie Mellon's Software Engineering Institute in the late 19905. By 2010, the Defense Information Systems Agency revised its cyber strategy and established the Program Executive Officer-Mission Assurance. This highlights a shift from simply protecting data to balancing risk and begins a necessary dialogue to establish a cyber security roadmap. The Military Operations Research Society has recommended a cyber community of practice, recognizing there are too few professionals having both cyber and analytic experience. The authors characterize the limited body of knowledge in this symbiotic relationship. This paper identifies operational and research requirements for mission assurance M&S supporting defense and homeland security. M&S techniques are needed for enterprise oversight of cyber investments, test and evaluation, policy, training, and analysis.

Gendron, Gerald↗

Electroactive ZnO: Mechanisms, Conductivity, and Advances in Zn Alkaline Battery Cycling

Zinc oxide is of great interest for advanced energy devices because of its low cost, wide direct bandgap, non-toxicity, and facile electrochemistry. In zinc alkaline batteries, ZnO plays a critical role in electrode passivation, a process that hinders commercialization and remains poorly understood. Here, novel observations of an electroactive type of ZnO formed in Zn-metal alkaline electrodes are disclosed. The electrical conductivity of battery-formed ZnO is measured and found to vary by factors of up to 104, which provides a first-principles-based understanding of Zn passivation in industrial alkaline batteries. Simultaneous with this conductivity change, protons are inserted into the crystal structure and electrons are inserted into the conduction band in quantities up to ≈1020 cm−3 and ≈1 mAh gZnO−1. Electron insertion causes blue electrochromic coloration with efficiencies and rates competitive with leading electrochromic materials. The electroactivity of ZnO is evidently enabled by rapid crystal growth, which forms defects that complex with inserted cations, charge-balanced by the increase of conduction band electrons. This property distinguishes electroactive ZnO from inactive classical ZnO. Knowledge of this phenomenon is applied to improve cycling performance of industrial-design electrodes at 50% zinc utilization and the authors propose other uses for ZnO such as electrochromic devices.

Brendan E. Hawkins↗

Electroactive ZnO: Mechanisms, Conductivity, and Advances in Zn Alkaline Battery Cycling

Zinc oxide is of great interest for advanced energy devices because of its low cost, wide direct bandgap, non-toxicity, and facile electrochemistry. In zinc alkaline batteries, ZnO plays a critical role in electrode passivation, a process that hinders commercialization and remains poorly understood. Here, novel observations of an electroactive type of ZnO formed in Zn-metal alkaline electrodes are disclosed. The electrical conductivity of battery-formed ZnO is measured and found to vary by factors of up to 10 4 , which provides a first-principles-based understanding of Zn passivation in industrial alkaline batteries. Simultaneous with this conductivity change, protons are inserted into the crystal structure and electrons are inserted into the conduction band in quantities up to ≈10 20 cm –3 and ≈1 mAh gZnO –1 . Electron insertion causes blue electrochromic coloration with efficiencies and rates competitive with leading electrochromic materials. The electroactivity of ZnO is evidently enabled by rapid crystal growth, which forms defects that complex with inserted cations, charge-balanced by the increase of conduction band electrons. Furthermore, this property distinguishes electroactive ZnO from inactive classical ZnO. Knowledge of this phenomenon is applied to improve cycling performance of industrial-design electrodes at 50% zinc utilization and the authors propose other uses for ZnO such as electrochromic devices.

36 MATERIALS SCIENCE↗

Improving the Discovery Power of the Dark Energy Survey Gravitational Wave Program in Its Fourth Observing Campaign

The universe is growing at an accelerated rate, yet the several experiments and science cases used to measure this property yield conflicting results for the rate. Known colloquially as the Hubble tension problem, this discrepancy calls for a novel measurement of the Hubble Constant, H0, in order to be resolved. The Dark Energy Survey Gravitational Wave group (DESGW) aims to relieve this tension by performing a standard sirens measurement of H0 independent of traditional methods. To do so in the current era of data abundance and limited telescope time demands a robust, optimized, and complete science software pipeline to carefully balance the transition from gravitational wave data to state-of-the-art images, images to photometric data, and photometric data to identification and analysis of electromagnetic counterparts to gravitational wave signals. This thesis details the contributions of the author to the DESGW Search & Discovery Pipeline for the fourth observing run of the LIGO/Virgo/KAGRA gravitational wave detector network, as well as the science applications that have been pursued.

79 ASTRONOMY AND ASTROPHYSICS↗

The space-time solution element method: A new numerical approach for the Navier-Stokes equations

This paper is one of a series of papers describing the development of a new numerical method for the Navier-Stokes equations. Unlike conventional numerical methods, the current method concentrates on the discrete simulation of both the integral and differential forms of the Navier-Stokes equations. Conservation of mass, momentum, and energy in space-time is explicitly provided for through a rigorous enforcement of both the integral and differential forms of the governing conservation laws. Using local polynomial expansions to represent the discrete primitive variables on each cell, fluxes at cell interfaces are evaluated and balanced using exact functional expressions. No interpolation or flux limiters are required. Because of the generality of the current method, it applies equally to the steady and unsteady Navier-Stokes equations. In this paper, we generalize and extend the authors' 2-D, steady state implicit scheme. A general closure methodology is presented so that all terms up through a given order in the local expansions may be retained. The scheme is also extended to nonorthogonal Cartesian grids. Numerous flow fields are computed and results are compared with known solutions. The high accuracy of the scheme is demonstrated through its ability to accurately resolve developing boundary layers on coarse grids. Finally, we discuss applications of the current method to the unsteady Navier-Stokes equations.

Scott, James R.↗

Status report on emerging photovoltaics

This report provides a snapshot of emerging photovoltaic (PV) technologies. It consists of concise contributions from experts in a wide range of fields including silicon, thin film, III-V, perovskite, organic, and dye-sensitized PVs. Strategies for exceeding the detailed balance limit and for light managing are presented, followed by a section detailing key applications and commercialization pathways. A section on sustainability then discusses the need for minimization of the environmental footprint in PV manufacturing and recycling. The report concludes with a perspective based on broad survey questions presented to the contributing authors regarding the needs and future evolution of PV.

14 SOLAR ENERGY↗