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At least 163 records · Page 9

A Radiation-Tolerant, Low-Power Non-Volatile Memory Based on Silicon Nanocrystal Quantum Dots

Nanocrystal nonvolatile floating-gate memories are a good candidate for space applications - initial results suggest they are fast, more reliable and consume less power than conventional floating gate memories. In the nanocrystal based NVM device, charge is not stored on a continuous polysilicon layer (so-called floating gate), but instead on a layer of discrete nanocrystals. Charge injection and storage in dense arrays of silicon nanocrystals in SiO2 is a critical aspect of the performance of potential nanocrystal flash memory structures. The ultimate goal for this class of devices is few- or single-electron storage in a small number of nanocrystal elements. In addition, the nanocrystal layer fabrication technique should be simple, 8-inch wafer compatible and well controlled in program/erase threshold voltage swing was seen during 100,000 program and erase cycles. Additional near-term goals for this project include extensive testing for radiation hardness and the development of artificial layered tunnel barrier heterostructures which have the potential for large speed enhancements for read/write of nanocrystal memory elements, compared with conventional flash devices. Additional information is contained in the original extended abstract.

Bell, L. D.↗

Performance of Optimized Actuator and Sensor Arrays in an Active Noise Control System

Experiments have been conducted in NASA Langley s Acoustics and Dynamics Laboratory to determine the effectiveness of optimized actuator/sensor architectures and controller algorithms for active control of harmonic interior noise. Tests were conducted in a large scale fuselage model - a composite cylinder which simulates a commuter class aircraft fuselage with three sections of trim panel and a floor. Using an optimization technique based on the component transfer functions, combinations of 4 out of 8 piezoceramic actuators and 8 out of 462 microphone locations were evaluated against predicted performance. A combinatorial optimization technique call tabu search was employed to select the optimum transducer arrays. Three test frequencies represent the cases of a strong acoustic and strong structural response, a weak acoustic and strong structural response and a strong acoustic and weak structural response. Noise reduction was obtained using a Time Averaged/Gradient Descent (TAGD) controller. Results indicate that the optimization technique successfully predicted best and worst case performance. An enhancement of the TAGD control algorithm was also evaluated. The principal components of the actuator/sensor transfer functions were used in the PC-TAGD controller. The principal components are shown to be independent of each other while providing control as effective as the standard TAGD.

Palumbo, D. L.↗

A radiation - tolerant, low - power non - volatile memory based on silicon nanocrystal quantum dots.

Nanocrystal nonvolatile floating-gate memories are a good candidate for space applications - initial results suggest they are fast, more reliable and consume less power than conventional floating gate memories. In the nanocrystal based NVM device, charge is not stored on a continuous polysilicon layer (so-called floating gate), but instead on a layer of discrete nanocrystals. Charge injection and storage in dense arrays of silicon nanocrystals in Si02 is a critical aspect of the performance of potential nanocrystal flash memory structures. The ultimate goal for this class of devices is few- or single-electron storage in a small number of nanocrystal elements. In addition, the nanocrystal layer fabrication technique should be simple, 8-inch wafer compatible and well controlled.

Green, M. L.↗

Solar power satellite system definition study. Part 2, volume 8: SPS launch vehicle ascent and entry sonic overpressure and noise effects

Recoverable launch vehicle concepts for the Solar Power Satellite program were identified. These large launch vehicles are powered by proposed engines in the F-1 thrust level class. A description of the candidate launch vehicles and their operating mode was provided. Predictions of the sonic over pressures during ascent and entry for both types of vehicles, and prediction of launch noise levels in the vicinity of the launch site were included. An overall assessment and criteria for sonic overpressure and noise levels was examined.

Source record↗

The nature of the emission-line nebulae in powerful far-infrared galaxies

The authors discuss their program of narrow-band (H alpha + (NII)) imaging of a sample of 30 powerful far-infrared galaxies (FIRG's) chosen to have far-infrared spectral energy distributions similar to the prototype FIRG's Arp 220, NGC 3690, NGC 6240, and M82. The emission-line nebulae of these IR color-selected sample (ICSS) galaxies as a class are both impressively large (mean half light radius, r approx. 1.3 Kpc, and mean diameter, D approx. 16 Kpc) and luminous (L sub TOT approx. 10(exp 8) solar lumninosity; uncorrected for internal extinction). The mean total H alpha + (NII) luminosity of the FIRG's is comparable to that found for pairs of optically selected interacting galaxies (Bushouse, Lamb, and Werner 1988), but is a factor of approx. 5 greater than that of isolated spirals (Kennicutt and Kent 1983). Only approx. 25 percent of the nearby (z approx. less than 0.10) FIRG's have morphologies suggesting that large HII-regions contribute significantly to their emission-line appearance. The broad-band morphologies of our IR color-selected galaxies fall into three major categories. Nearly 75 percent are single galaxy systems, with the remaining FIRG's being either multiple nuclei systems, or members of interacting pairs. Since the authors saw few (10 percent) currently interacting FIRG's, yet many (80 percent) with highly distorted continuum morphologies, their IR color criteria may be preferentially selecting galaxies that have undergone highly inelastic, rapidly merging interactions.

Armus, Lee↗

New Developments and Research Findings: NASA Hydrazine Arcjets

In 1984, the market for commercial geosynchronous communications satellites (comsats) was expanding and there was strong competition between spacecraft builders for market share. The propellant required for the north-south stationkeeping (NSSK) function was a major mission limiter, and the small chemical and resistojet systems then in use were at or near their physical limits. Thus, conditions were right for the development of a high performance NSSK system, and after an extensive survey of both propulsion technologies and the aerospace community, the NASA program chose hydrazine arcjets for development. A joint government/industry development program ensued which culminated in the acceptance of arcjet technology. NASA efforts included fundamental feasibility assessments, hardware development and verification, and multiple efforts aimed at the demonstration of critical operational characteristics of arcjet systems. Throughout the program, constant contact with the user community was maintained to determine system requirements. Both contracted and cooperative programs with industry were supported. First generation, kW-class arcjets are now operational for NSSK on the Telstar 401 satellite launched in December of 1993 and are baselined for use on multiple future satellite series (Intelsat 8, AsiaSat, Echostar). Arcjet development efforts are now focusing on the development of both high performance (600 s), 2 kW thrusters for application on next generation comsats and low power (Pe approximately 0.5 kW) for a variety of applications on power limited satellites. This paper presents a review of the NASA's role in the development of hydrazine arcjets with a focus on approaches, lessons learned, and the future.

Curren, Francis M.↗

NASA Software Engineering Benchmarking Study

To identify best practices for the improvement of software engineering on projects, NASA's Offices of Chief Engineer (OCE) and Safety and Mission Assurance (OSMA) formed a team led by Heather Rarick and Sally Godfrey to conduct this benchmarking study. The primary goals of the study are to identify best practices that: Improve the management and technical development of software intensive systems; Have a track record of successful deployment by aerospace industries, universities [including research and development (R&D) laboratories], and defense services, as well as NASA's own component Centers; and Identify candidate solutions for NASA's software issues. Beginning in the late fall of 2010, focus topics were chosen and interview questions were developed, based on the NASA top software challenges. Between February 2011 and November 2011, the Benchmark Team interviewed a total of 18 organizations, consisting of five NASA Centers, five industry organizations, four defense services organizations, and four university or university R and D laboratory organizations. A software assurance representative also participated in each of the interviews to focus on assurance and software safety best practices. Interviewees provided a wealth of information on each topic area that included: software policy, software acquisition, software assurance, testing, training, maintaining rigor in small projects, metrics, and use of the Capability Maturity Model Integration (CMMI) framework, as well as a number of special topics that came up in the discussions. NASA's software engineering practices compared favorably with the external organizations in most benchmark areas, but in every topic, there were ways in which NASA could improve its practices. Compared to defense services organizations and some of the industry organizations, one of NASA's notable weaknesses involved communication with contractors regarding its policies and requirements for acquired software. One of NASA's strengths was its software assurance practices, which seemed to rate well in comparison to the other organizational groups and also seemed to include a larger scope of activities. An unexpected benefit of the software benchmarking study was the identification of many opportunities for collaboration in areas including metrics, training, sharing of CMMI experiences and resources such as instructors and CMMI Lead Appraisers, and even sharing of assets such as documented processes. A further unexpected benefit of the study was the feedback on NASA practices that was received from some of the organizations interviewed. From that feedback, other potential areas where NASA could improve were highlighted, such as accuracy of software cost estimation and budgetary practices. The detailed report contains discussion of the practices noted in each of the topic areas, as well as a summary of observations and recommendations from each of the topic areas. The resulting 24 recommendations from the topic areas were then consolidated to eliminate duplication and culled into a set of 14 suggested actionable recommendations. This final set of actionable recommendations, listed below, are items that can be implemented to improve NASA's software engineering practices and to help address many of the items that were listed in the NASA top software engineering issues. 1. Develop and implement standard contract language for software procurements. 2. Advance accurate and trusted software cost estimates for both procured and in-house software and improve the capture of actual cost data to facilitate further improvements. 3. Establish a consistent set of objectives and expectations, specifically types of metrics at the Agency level, so key trends and models can be identified and used to continuously improve software processes and each software development effort. 4. Maintain the CMMI Maturity Level requirement for critical NASA projects and use CMMI to measure organizations developing software for NASA. 5.onsolidate, collect and, if needed, develop common processes principles and other assets across the Agency in order to provide more consistency in software development and acquisition practices and to reduce the overall cost of maintaining or increasing current NASA CMMI maturity levels. 6. Provide additional support for small projects that includes: (a) guidance for appropriate tailoring of requirements for small projects, (b) availability of suitable tools, including support tool set-up and training, and (c) training for small project personnel, assurance personnel and technical authorities on the acceptable options for tailoring requirements and performing assurance on small projects. 7. Develop software training classes for the more experienced software engineers using on-line training, videos, or small separate modules of training that can be accommodated as needed throughout a project. 8. Create guidelines to structure non-classroom training opportunities such as mentoring, peer reviews, lessons learned sessions, and on-the-job training. 9. Develop a set of predictive software defect data and a process for assessing software testing metric data against it. 10. Assess Agency-wide licenses for commonly used software tools. 11. Fill the knowledge gap in common software engineering practices for new hires and co-ops.12. Work through the Science, Technology, Engineering and Mathematics (STEM) program with universities in strengthening education in the use of common software engineering practices and standards. 13. Follow up this benchmark study with a deeper look into what both internal and external organizations perceive as the scope of software assurance, the value they expect to obtain from it, and the shortcomings they experience in the current practice. 14. Continue interactions with external software engineering environment through collaborations, knowledge sharing, and benchmarking.

Rarick, Heather L.↗

Pyroelectric conversion in space: A conceptual design study

Pyroelectric conversion is potentially a very lightweight means of providing electrical power generation in space. Two conceptualized systems approaches for the direct conversion of heat (from sunlight) into electrical energy using the pyroelectric effect of a new class of polar polymers were evaluated. Both of the approaches involved large area thin sheets of plastic which are thermally cycled by radiative input and output of thermal energy. The systems studied are expected to eventually achieve efficiencies of the order of 8% and may deliver as much as one half kilowatt per kilogram. In addition to potentially very high specific power, the pyroelectric conversion approaches outlined appear to offer low cost per watt in the form of an easily deployed, flexible, strong, electrically ""self-healing'', and high voltage sheet. This study assessed several potential problems such as plasma interactions and radiation degradation and suggests approaches to overcome them. The fundamental technological issues for space pyroelectric conversion are: (1) demonstration of the conversion cycle with the proposed class of polymers, (2) achievement of improved dielectric strength of the material, (3) demonstration of acceptable plasma power losses for low altitude, and (4) establishment of reasonable lifetime for the pyroelectric material in the space environment. Recommendations include an experimental demonstration of the pyroelectric conversion cycle followed by studies to improve the dielectric strength of the polymer and basic studies to discover additional pyroelectric materials.

Olsen, R. B.↗

G0.9 + 0.1 and the emerging class of composite supernova remnants

High-resolution, multifrequency maps of a bright extended radio source near the Galactic center have revealed it to be a classic example of a composite supernova remnant. A steep-spectrum shell of emission, about 8 arcmin in diameter, surrounds a flat-spectrum, highly polarized Crab-like core about 2 arcmin across. The two components have equal flux densities at about 6 cm, marking this source as having the highest core-to-shell ratio among the about 10 composite remnants identified to date. X-ray and far-infrared data on the source are used to constrain the energetics and evolutionary state of the remnant and its putative central pulsar. It is argued that the total energy contained in the Crab-like components requires that the pulsars powering them were all born with periods shorter than 50 ms, and that if a substantial number of neutron stars with slow initial rotation rates exist, their birthplaces have not yet been found.

Helfand, D. J.↗

Satellite remote sensing of total dry matter production in the Senegalese Sahel

Nine predominantly cloud-free NOAA-7 advanced very high resolution radiometer images were obtained during a three-month period during the 1981 rainy season in the Sahel of Senegal. The 0.55-0.68- and 0.725-1.10-micron channels were used to form the normalized difference green leaf density vegetation index and the 11.5-12.5-micron channel was used as a cloud mask for each of the nine images. Changes in the normalized difference values among the various dates were closely associated with precipitation events. Six of the images spanning an 8-week period were used to generate a cumulative integrated index. Ground biomas samplings in the 30,000 sq km study area were used to assign total dry biomass classes to the cumulative index.

Tucker, C. J.↗

The Genesis Solar Wind Sample Return Mission

The Genesis spacecraft was launched on August 8 from Cape Canaveral on a journey to become the first spacecraft to return from interplanetary space. The fifth in NASA's line of low-cost Discovery-class missions, its goal is to collect samples of solar wind and return them to Earth for detailed isotopic and elemental analysis. The spacecraft is to collect solar wind for over two years, while circling the L1 point 1.5 million km sunward of the earth, before heading back for a capsule-style re-entry in September, 2004. After parachute deployment, a mid-air helicopter recovery will be used to avoid a hard landing. The mission has been in the planning stages for over ten years. Its cost, including development, mission operations, and sample analysis, is approximately $209M. The Genesis science team, headed by principal investigator Donald Burnett of Caltech, consists of approximately 20 co-investigators from universities and science centers around the country and internationally. The spacecraft consists of a relatively flat spacecraft bus containing most of the subsystem components, situated below a sample return capsule (SRC) which holds the solar-wind collection substrates and an electrostatic solar wind concentrator. Some of the collectors are exposed throughout the collection period, for a sample of bulk solar wind, while others are exposed only to certain solar wind regimes, or types of flow. Ion and electron spectrometers feed raw data to the spacecraft control and data-handling (C&DH) unit, which determines ion moments and electron flux geometries in real time. An algorithm is used to robotically decide between interstream (IS), coronal hole (CH), and coronal mass ejection (CME) regimes, and to control deployment of the proper arrays to sample these wind regimes independently. This is the first time such a solar-wind decision algorithm has been used on board a spacecraft.

Wiens, Roger C.↗

Increased walking variability in elderly persons with congestive heart failure

OBJECTIVES: To determine the effects of congestive heart failure on a person's ability to walk at a steady pace while ambulating at a self-determined rate. SETTING: Beth Israel Hospital, Boston, a primary and tertiary teaching hospital, and a social activity center for elderly adults living in the community. PARTICIPANTS: Eleven elderly subjects (aged 70-93 years) with well compensated congestive heart failure (NY Heart Association class I or II), seven elderly subjects (aged 70-79 years) without congestive heart failure, and 10 healthy young adult subjects (aged 20-30 years). MEASUREMENTS: Subjects walked for 8 minutes on level ground at their own selected walking rate. Footswitches were used to measure the time between steps. Step rate (steps/minute) and step rate variability were calculated for the entire walking period, for 30 seconds during the first minute of the walk, for 30 seconds during the last minute of the walk, and for the 30-second period when each subject's step rate variability was minimal. Group means and 5% and 95% confidence intervals were computed. MAIN RESULTS: All measures of walking variability were significantly increased in the elderly subjects with congestive heart failure, intermediate in the elderly controls, and lowest in the young subjects. There was no overlap between the three groups using the minimal 30-second variability (elderly CHF vs elderly controls: P < 0.001, elderly controls vs young: P < 0.001), and no overlap between elderly subjects with and without congestive heart failure when using the overall variability. For all four measures, there was no overlap in any of the confidence intervals, and all group means were significantly different (P < 0.05).

NASA Discipline Cardiopulmonary↗

2005 PathfinderPlus Aero-Elastic Research Flight

This viewgraph presentation describes the 2005 Pathfinder along with an investigation of its aeroelastic responses. The contents include: 1) HALE Class of Vehicles; 2) Aero-elastic Research Flights Overall Objective; 3) General Arrangement; 4) Sensor Locations; 5) NASA Ramp Operations; 6) Lakebed Operations; 7) 1st Flight Data Set; 8) Tool development / data usage; 9) HALE Tool Development & Validation; 10) Building a HALE Foundation; 11) Compelling Needs Drive HALE Efforts; and 12) Team Photo

Navarro, Robert↗

Detection of silicate emission features in the 8- to 13-micron spectra of main belt asteroids

A presentation is given of 8.0-13.0 micron spectra (Delta lambda/lambda = 0.02-0.03) for six main belt asteroids, which range from 58 to 220 km in diameter and sample the five principal taxonomic classes (C, S, M, R and E). Narrow, well-defined silicate emission features are present on two of the asteroids, the C-type 19 Fortuna and the M-type 21 Lutetia. No comparable emission features are observed on the S-types 11 Parthenope and 14 Irene, the R-type 349 Dembowska or the E-type 64 Angelina.

Feierberg, M. A.↗

Multispectral, thermal infrared satellite data for geologic applications

The value of multispectral thermal infrared satellite data for geologic mapping was assessed, applying the principal component and canonical analysis techniques to the images of the central part of the Arabian Peninsula (a 200 x 300 km area). Low resolution thermal infrared (TIR) data from the Nimbus 5 Surface Composition Mapping Radiometer (SCMR) and the NOAA-7 Advanced Very High Resolution Radiometer (AVHRR) were used. Color images included an 8.8 micrometer (SCMR) and 3.7 and 10.8 micrometer (AVHRR-night) data, ratioed AVHRR day/night TIR data, ratioed AVHRR reflected radiation data, and transformed 8- and 10-band TIR plus reflected radiation data. The results clearly demonstrated the potential geologic value of multispectral TIR data. Igneous and metamorphic units could be separated as a class (although not from each other except for young calc-alkaline granites). Some previously unmapped extensions of mapped faults below thick sedimentary units could be delineated. No single enhancement technique displayed all the potential information, implying that they should be used together.

Blodget, H. W.↗

Message Mode Operations for Spacecraft: A Proposal for Operating Spacecraft During Cruise and Mitigating the Network Loading Crunch

The NASA Deep Space Network (DSN) is a world-class spacecraft tracking facility with stations located in Spain, Australia and USA, servicing Deep Space Missions of many space agencies. The current system of scheduling spacecraft during cruise for multiple 8 hour tracking sessions per week currently leads to an overcommitted DSN. Studies indicate that future projected mission demands upon the Network will only make the loading problem worse. Therefore, a more efficient scheduling of DSN resources is necessary in order to support the additional network loading envisioned in the next few years: The number of missions is projected to increase from 25 in 1998 to 34 by 2001. In fact given the challenge of the NASA administrator, Dan Goldin, of launching 12 spacecraft per year, the DSN would be tracking approximately 90 spacecraft by 2010. Currently a large amount of antenna time and network resources are subscribed by a project in order to have their mission supported during the cruise phase. The recently completed Mars Pathfinder mission was tracked 3 times a week (8 hours/day) during the majority of its cruise to Mars. This paper proposes an innovative approach called Message Mode Operations (MMO) for mitigating the Network loading problem while continuing to meet the tracking, reporting, time management, and scheduling requirements of these missions during Cruise while occupying very short tracking times. MMO satisfies these requirements by providing the following services: Spacecraft Health and Welfare Monitoring Service Command Delivery Service Adaptive Spacecraft Scheduling Service Orbit Determination Service Time Calibration Service Utilizing more efficient engineering telemetry summarization and filtering techniques on-board the spacecraft and collapsing the navigation requirements for Doppler and Range into shorter tracks, we believe spacecraft can be adequately serviced using short 10 to 30 minute tracking sessions. This claim assumes that certain changes would have to he made in the way the Network traditionally services missions in Cruise. Furthermore, limiting spacecraft to short sessions will free up larger blocks of time in the tracking schedule to help accommodate future tracking demands soon to be placed upon the Network. This paper describes the key characteristics and benefits of MMO, the operational scenarios for its use, the required changes to the ground system in order to make this approach feasible and the results of two simulations: 1) to determine the effects of MMO on projected mission loading on the DSN and, 2) to determine the effect MMO has on spacecraft orbit determination.

Greenberg, Ed↗

LECTURE 8: Understanding Global Cloud Radiative Impacts

The influence of clouds on the radiation budget is one of the most important facets of the Earth’s climate. Satellite observations in the last 35 years have helped us understand the bulk radiative effects of different classes of clouds. Bill Rossow has spearheaded efforts in that direction, demonstrating the value of the International Satellite Cloud Climatology Project (ISCCP) cloud retrievals as a foundation for the full reconstruction of Earth’s Radiation Budget components. This main aim of this document is to provide an overview of the global radiative impacts of clouds at annual time scales. While geographical and seasonal aspects receive some attention, it is cloud radiative effect decomposition by cloud category (or“class” ) that is the main focal point. Furthermore, this document addresses the large-scale radiative behavior of clouds only for the current climate, with no further discussion of how this behavior may change in the future and what its climatic impact may be [please refer to Del Genio (2018) for an excellent overview of this topic]. Cloud classes can be defined in many ways, and are often referred to with terms such as “cloud type”and “cloud regime”. Some of the definitions are more meaningful at the level of individual instrument footprints (“pixels” for passive or “rays” for active satellite observations) while others for larger areas (e.g., “mesoscale”).This distinction will become apparent below.

Lazaros Oreopoulos↗

Buckling Test and Analysis of the 8-Foot-Diameter Sandwich Composite Cylinder Test Article CTA8.2 as Part of the Shell Buckling Knockdown Factor Project: Test Dates 5-7 December 2017

It is well known that the buckling response of thin shell structures can be sensitive to small imperfections in the geometry and loading. The NASA Engineering and Safety Center (NESC) Shell Buckling Knockdown Factor Project (SBKF) has the goal of developing buckling design recommendations for select classes of metallic and composite shells. Part of completed SBKF work is described in this report. In particular, the test and analysis results from the second SBKF composite test article, CTA8.2, are described. This test was the second in a series of tests on sandwich composite cylinders that can be used to experimentally validate analysis methods, which in turn can be used to develop analysis-based shell buckling design guidelines for sandwich composite launch-vehicle cylindrical structures. CTA8.2 was an 8-foot diameter honeycomb-core sandwich cylinder that was fabricated and tested at the Marshall Space Flight Center (MSFC). The primary objectives of this test were to interrogate the structural capability of the composite test article, and to verify the test-article design and analysis approach for cylinders subjected to axial compression loads. This report contains the descriptions of the test-article design, fabrication, and test. The pre-test modeling and analysis methods, and corresponding results used in support of the test-article design and test planning, are also described. Additional post-test modeling and analysis efforts and results follow. Selected test results are compared to pre-test predictions and post-test analyses.

Adam Przekop↗