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NASA NTRS1971

Buckling analysis for axially compressed flat plates, structural sections, and stiffened plates reinforced with laminated composites

A classical buckling analysis is developed for stiffened, flat plates composed of a series of linked plate and beam elements. Plates are idealized as multilayered orthotropic elements. Structural beads and lips are idealized as beams. The loaded edges of the stiffened plate are simply-supported and the conditions at the unloaded edges can be prescribed arbitrarily. The plate and beam elements are matched along their common junctions for displacement continuity and force equilibrium in an exact manner. Offsets between elements are considered in the analysis. Buckling under uniaxial compressive load for plates, sections, and stiffened plates is investigated. Buckling loads are the lowest of all possible general and local failure modes, and the mode shape is used to determine whether buckling is a local or general instability. Numerical correlations with existing analysis and test data for plates, sections, and stiffened plates including boron-reinforced structures are discussed. In general correlations are reasonably good.

Viswanathan, A. V.↗

NASA NTRS1989

Meteoritic basalts

The objectives were to: explain the abundances of siderophile elements in the SNC meteorite suite, of putative Martian origin; discover the magmatic origins and possibly magma compositions behind the Nakhla meteorite, one of the SNC meteorites; and a re-evaluation of the petrology of Angra dos Reis, a unique meteorite linked to the earliest planetary bodies of the solar nebula. A re-evaluation of its petrography showed that the accepted scenario for its origin, as a cumulate igneous rock, was not consistent with the meteorite's textures (Treiman). More likely is that the meteorite represents a prophyritic igneous rock, originally with magma dominant. Studies of the Nakhla meteorite, of possible Martian origin, although difficult, were successful. It became necessary to reject the basic categorization of Nakhla: that is was a cumulate igneous rock. Detailed studies of the chemical zoning of Nakhlas' minerals, coupled with the failure of experimental studies to yield expected results, forced the conclusion that Nakhla is not a cumulate rock in the usual sense: a rock composed of igneous crystals and intercrystal magma. Study of the siderophile element abundances in the SNC meteorite groups involved trying to find reasonable core formation processes and parameters that would reproduce the observed abundances. Modelling was successful, and delimited a range of models which overlap with those reasonable from geophysical constraints.

Treiman, Allan H.↗

NASA NTRS1998

Microgravity Science in Space Flight Gloveboxes

Microgravity science studies the influences of gravity on phenomena in fluids, materials processes, combustion, and human cell growth in the low acceleration environment of space flight. During the last decade, the accomplishment of the flight research in the field has evolved into an effective cooperation between the flight crew in the Shuttle and the ground-based investigator using real-time communication via voice and video links. This team structure has led to interactive operations in which the crew performs the experimentation while guided, as necessary, by the science investigator who formulated the investigation and who will subsequently interpret and analyze the data. One of the primary challenges to implementing this interactive research has been the necessity of structuring a means of handling fluids, gases, and hazardous materials in a manned laboratory that exhibits the novelty of weightlessness. Developing clever means of designing experiments in closed vessels is part of the solution- but the space flight requirement for one and two failure-tolerant containment systems leads to serious complications in the physical handling of sample materials. In response to the conflict between the clear advantage of human operation and judgment, versus the necessity to isolate the experiment from the crewmember and the spacecraft environment, the Microgravity Research Program has initiated a series of Gloveboxes in the various manned experiment carriers. These units provide a sealed containment vessel whose interior is under a negative pressure with respect to the ambient environment but is accessible to a crewmember through the glove ports.

Baugher, Charles↗

NASA NTRS2022

Qualification and Performance of a High-Efficiency Laser Transmitter for Deep-Space Optical Communications

A high-power Laser Transmitter Assembly (LTA) was developed to support the Deep Space Optical Communications (DSOC) technology demonstration being developed by the Jet Propulsion Laboratory. NASA’s Psyche Mission plans to host the DSOC flight subsystem for testing space-to-ground high-bandwidth laser communications en route to the 16 Psyche asteroid. We review the design, performance, and qualification of the LTA Engineering Model and Flight Model (EM and FM) delivered to JPL. The LTA uses a master-oscillator power amplifier (MOPA) design and delivers up to 4.5 W at 1550 nm, with a highly efficient, cladding-pumped, polarization-maintaining erbium-ytterbium fiber amplifier. The master oscillator generates a range of pulse widths and repetition rates to support modulation formats from 16- to 128-PPM for optical data transmission at >100 Mbps. The LTA was designed for high reliability and radiation hardness, and includes redundant signal and pumping paths to reduce single points of failure, hardware interlocks to ensure safe operation and protection against damage, closed-loop control of optical power, and detailed health and status via telemetry. The LTA EM and FM were subjected to unit-appropriate space qualification testing. We describe the performance testing of the EM and FM, for the characterization of key metrics such as wavelength stability, signal linewidth, optical pulse width, jitter, and extinction ratio, and polarization extinction ratio. The management of optical nonlinearities (self-phase modulation, Brillouin scattering, or pulse-to-pulse energy variation), which could result in an optical link penalty or damage to the LTA, is also detailed, and factors affecting the power efficiency are discussed.

Jaques, J.↗

NASA NTRS1972

Buckling analysis for structural sections and stiffened plates reinforced with laminated composites.

A classical buckling analysis is developed for stiffened, flat plates composed of a series of linked flat plate and beam elements. Plates are idealized as multilayered orthotropic elements; structural beads and lips are idealized as beams. The loaded edges of the stiffened plate are simply supported and the conditions at the unloaded edges can be prescribed arbitrarily. The plate and beam elements are matched along their common junctions for displacement continuity and force equilibrium in an exact manner. Offsets between elements are considered in the analysis. Buckling under uniaxial compressive load for plates, sections and stiffened plates is investigated. Buckling loads are found as the lowest of all possible general and local failure modes and the mode shape is used to determine whether buckling is a local or general instability. Numerical correlations with existing analysis and test data for plates, sections and stiffened plates including boron-reinforced structures are discussed. In general, correlations are reasonably good.

Viswanathan, A. V.↗

NASA NTRS2019

Reinforcing Additives for Ice Adhesion Reduction Coatings

Adhesion of contaminants has been identified as a ubiquitous issue for aeronautic exterior surfaces. In-flight icing is particularly hazardous for all aircraft and can be experienced throughout the year under the appropriate environmental conditions. On larger vehicles, the accretion of ice could result in loss of lift, engine failure, and potentially loss of vehicle and life were it not for active deicing or anti-icing equipment. Smaller vehicles though cannot support the mass and mechanical complexity of active ice mitigating systems and thus must rely upon passive approaches or avoid icing conditions altogether. One approach that may be applicable to all aircraft is the use of coatings. Durability remains an issue and has prevented realization of coatings for leading edge contamination mitigation. In this work, epoxy coatings were generated as a passive approach for ice adhesion mitigation and methods to improve durability were evaluated. Highly cross-linked epoxy systems can be extremely rigid, which could have deleterious consequences regarding application as a leading edge coating. Incorporation of flexible species, such as poly(ethylene glycol) may improve coating toughness.8 Additionally, core-shell rubber (CSR) particles have been utilized to improve fracture toughness of epoxies.9 Both of these more established additives are investigated in this work. An emerging additive that is also evaluated here is holey graphene. This nanomaterial possesses many of the advantageous properties of graphene (excellent mechanical properties, thermal and electrical conductivity, large surface area, etc.) while also exhibiting behaviors associated with flexible, porous materials (i.e., compressibility, increased permeation, etc.). Holey graphene, HG, was synthesized by the oxidation of defect-rich sites on graphene sheets through controlled thermal expo-sure.10 It is envisioned that the porous nature of HG would allow resin penetration through the graphitic plane, resulting in better interfacial interaction and therefore better translation of the nanomaterial’s properties to the surrounding matrix.

Wohl, Christopher J↗

NASA NTRS2018

Modeling In-Space Aborts for NASA Human Exploration Missions

NASA is developing new capabilities to send humans beyond low Earth orbit (LEO) for the first time in several decades with the new Multi-purpose Crew Vehicle (MPCV) Orion spacecraft and Space Launch System (SLS) launch vehicle. As part of these capabilities, NASA is developing means to terminate missions prior to reaching mission destinations in order to save the crew in the event of critical life-threatening failures. This abort capability exists for both ascent and in-space operations. While the risk associated with ascent aborts has been modeled in detail, less has been done in the area of in-space aborts (e.g. Apollo 13). Recent efforts have started to better assess the risk associated with in-space aborts. This paper will describe these efforts. The in-space abort model described in this paper is part of a larger Cross-Program PRA (XPRA) model of exploration missions planned in the next few years to the vicinity of the Moon. The model consists of linked event trees and fault trees and associated rules built using the Systems Analysis Program for Hands-On Integrated Reliability Evaluations (SAPHIRE) tool. This model structure is being built with flexibility in mind in order to perform risk trades and further expansion of the model.

Bigler, Mark A.↗

NASA NTRS1990

A New Approximate Fracture Mechanics Analysis Methodology for Composites with a Crack or Hole

A new approximate theory which links the inherent flaw concept with the theory of crack tip stress singularities at a bi-material interface was developed. Three assumptions were made: (1) the existence of inherent flaw (i.e., damage zone) at the tip of the crack, (2) a fracture of the filamentary composites initiates at a crack lying in the matrix material at the interface of the matrix/filament, and (3) the laminate fails whenever the principal load-carrying laminae fails. This third assumption implies that for a laminate consisting of 0 degree plies, cracks into matrix perpendicular to the 0 degree filaments are the triggering mechanism for the final failure. Based on this theory, a parameter bar K sub Q which is similar to the stress intensity factor for isotropic materials but with a different dimension was defined. Utilizing existing test data, it was found that bar K sub Q can be treated as a material constant. Based on this finding a fracture mechanics analysis methodology was developed. The analytical results are correlated well with test results. This new approximate theory can apply to both brittle and metal matrix composite laminates with crack or hole.

Tsai, H. C.↗

NASA NTRS2019

Preface to the Special Collection: Recollections in Space Physics

Space Physics is a comparatively young scientific discipline, tightly linked to the era of satellite based investigations and the discoveries that came with it. As such, we as a community are fortunate to have met, been taught and mentored by, and even become friends with, many of those who were around to witness the birth of, and in many cases establish, our field. Each of these "Pioneers" have remarkable stories to tell. These accounts from the dawn of the space age provide a glimpse into that era of scientific discovery and are an important part of our collective history that deserve to be shared and commemorated. These are stories of perseverance, ingenuity, luck, and sometimes failure. We are fortunate to live in an era in which these distinguished scientists are still with us and able to share their experiences.To commemorate the 100th Anniversary of the American Geophysical Union (AGU), we have solicited a special collection of recollection papers to memorialize these experiences. This is not the first such effort to capture these stories. In 1994 (Vol. 99, No. A10, pp. 19,099-19,212) and again in 1996 (Vol. 101, No. A5, pp. 10,477-10,585) JGRSpace Physics published special sections entitled, "Pioneers of Space Physics," in celebration of AGU's 75th anniversary. Later, in 1997, Gilmore and Spreiter (1997) added a set of recollection papers on the discovery of the magnetosphere. Together, these papers containing personal accounts from the pioneers of the space age covered the period of roughly 1958-1967.It is our great honor to present retrospective papers from several of our distinguished colleagues who contributed significantly to the explosion in understanding of space physics and aeronomy that occurred from roughly 1967-1980. We chose to start at the end of the previous set of recollections and cover the decade of the 1970s, during which our field greatly expanded. It is also a time in which the second generation of space scientists entered the field and made foundational discoveries that continue to define our discipline.As with the previous papers, we asked the authors to "recount some of the events leading to the emergence of space physics and to put the events into a professional as well as personal perspective." (Gombosi et al.,1994). The authors of this special collection of recollections were selected following the same guidelines as the previous efforts. We started from a long list of senior colleagues and narrowed the list to roughly two dozen distinguished scientists based on discipline and geographic balance. Some of our colleagues, when asked, felt they would be unable to devote the time or energy to such a recollection and declined. Sadly,in the intervening 25 years since the original effort, some of our colleagues who were most active during the early years of the space age have passed. Therefore, this new special collection, 25 years after the first one, is timely with the AGU centennial celebrations, but late in fully capturing the stories of the pioneers of space physics. This is unfortunate and we encourage future editors of this journal to commission specialsections of legacy perspectives with a faster cadence than a quarter of a century.

Kepko, Emil L.↗

NASA NTRS1995

NASA Tech Briefs, November 1995

The contents include: 1) Mission Accomplished; 2) Resource Report: Marshall Space Flight Center; 3) NASA 1995 Software of the Year Award; 4) Microbolometers Based on Epitaxial YBa2Cu3O(sub 7-x) Thin Films; 5) Garnet Random-Access Memory; 6) Fabrication of SNS Weak Links on SOS Substrates; 7) High-Voltage MOSFET Switching Circuit; 8) Asymmetric Switching for a PWM H-Bridge Power Circuit; 9) Better Ohmic Contacts for InP Semiconductor Devices; 10) Low-Bandgap Thermovoltaic Materials and Devices; 11) Digital Frequency-Differencing Circuit; 12) Imaging Magnetometer; 13) Computer-Assisted Monitoring of a Complex System; 14) Buffered Telemetry Demodulator; 15) Compact Multifunction Inspection Head; 16) Optical Detection of Fractures in Ceramic Diaphragms; 17) Eddy-Current Detection of Cracks in Reinforced Carbon/Carbon; 18) Apparent Thermal Conductivity of Multilayer Insulation; 19) Optimizing Misch-Metal Compositions in Metal Hydride Anodes; 20) Device for Sampling Surface Contamination; 21) Probabilistic Failure Assessment for Fatigue; 22) Probabilistic Fatigue and Flaw-Propagation Analysis; 23) Windows Program for Driving the TDU-850 Printer; 24) Subband/Transform MATLAB Functions for Processing Images; 25) Computing Equilibrium Chemical Compositions; 26) Program Processes Thermocouple Readings; 27) ICAN-Second-Generation Integrated Composite Analyzer; 28) Integrated Composite Analyzer with Damping Capabilities; 29) Computing Efficiency of Transfer of Microwave Power; 30) Program Calculates Power Demands of Electronic Designs; 31) Cost-Estimation Program; 32) Program Estimates Areas Required by Electronic Designs; 33) Program to Balance Mapped Turbopump Assemblies; 34) BiblioTech; 35) Controlling Mirror Tilt With a Bimorph Actuator; 36) Burst-Disk Device Simulates Effect of Pyrotechnic Device; 37) Bearing-Mounting Concept Accommodates Thermal Expansion; 38) Parallel-Plate Acoustic Absorbers for Hot Environments; 39) Adjustable-Length Strut Withstands Large Cyclic Loads; 40) Tool Indicates Contact Angles in Bearing Raceways; 41) Gravity Slides With Magnetic Braking; 42) High-Torque, Lightweight, Pneumatically Driven Wrench for Small Spaces; 43) Device for Testing Compatibility of an O-Ring; 44) Magnetic Heat Pump Containing Flow Diverters; 45) Variable-Tilt Helicopter Rotor Mast; 46) "Beach-Ball" Robotic Rovers; 47) Apparatus Would Measure Temperatures of Ball Bearings; 48) Flexible Borescope for Inspecting Ducts; 49) Texturing Copper To Reduce Secondary Emission of Electrons; 50) Automated Laser Cutting in Three Dimensions; 51) Algorithm Helps Monitor Engine Operation; 52) Flexible Revision of Data-Processing Communications; 53) Software for Managing the Use of Land; 54) Thermal Strap Increases Cryocooling Efficiency; 55) Reversible Nut With Engagement Indication; 56) Control Algorithms for Kinematically Redundant Manipulators; 57) Computed Hydrogen-Flow Splits in a Rocket Engine; 58) Pressure and Thermal Modeling of Rocket Launches; 59) Field of View of a Spacecraft Antenna: Analysis and Software; 60) Digital Controller for Laser-Beam-Steering Subsystem; 61) More About Beam-Steering Subsystem for Laser Communication; 62) Digital Controller for Laser-Beam-Steering Subsystem: Part 2; 63) Interface Circuit Board for Space-Shuttle Communications; 64) Automated Planning of Spacecraft Telecommunications; 65) Artifacts of Spectral Analysis of Instrument Readings; 66) Neural-Network Controller for Vibration Suppression; 67) Adaptive Finite-Element Computation in Fracture Mechanics; 68) Attitude Control for the Cassini Spacecraft; 69) Analytical Model for Fluid Dynamics in a Microgravity Environment; 70) Study of Rocket-Engine Joints Bonded by NVCU/NARloy-Z; 71) Improved Silicon Nitride for Advanced Heat Engines; 72) Parameters for Welding Aluminum/Lithium Alloys; 73) Lightweight Composite Intertank Structure; 74) Foil Patches Seal Small Vacuum Leaks; 75) Data Base on Cables and Connectors; 76) Effect of Clock Mode on Radiation Hardnessf an ADC; and 77) Fault-Tolerant Control for a Robotic Inspection System.

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NASA NTRS2010

A Near-Term Concept for Trajectory Based Operations with Air/Ground Data Link Communication

An operating concept and required system components for trajectory-based operations with air/ground data link for today's en route and transition airspace is proposed. Controllers are fully responsible for separation as they are today, and no new aircraft equipage is required. Trajectory automation computes integrated solutions to problems like metering, weather avoidance, traffic conflicts and the desire to find and fly more time/fuel efficient flight trajectories. A common ground-based system supports all levels of aircraft equipage and performance including those equipped and not equipped for data link. User interface functions for the radar controller's display make trajectory-based clearance advisories easy to visualize, modify if necessary, and implement. Laboratory simulations (without human operators) were conducted to test integrated operation of selected system components with uncertainty modeling. Results are based on 102 hours of Fort Worth Center traffic recordings involving over 37,000 individual flights. The presence of uncertainty had a marginal effect (5%) on minimum-delay conflict resolution performance, and windfavorable routes had no effect on detection and resolution metrics. Flight plan amendments and clearances were substantially reduced compared to today s operations. Top-of-descent prediction errors are the largest cause of failure indicating that better descent predictions are needed to reliably achieve fuel-efficient descent profiles in medium to heavy traffic. Improved conflict detections for climbing flights could enable substantially more continuous climbs to cruise altitude. Unlike today s Conflict Alert, tactical automation must alert when an altitude amendment is entered, but before the aircraft starts the maneuver. In every other failure case tactical automation prevented losses of separation. A real-time prototype trajectory trajectory-automation system is running now and could be made ready for operational testing at an en route Center in 1-2 years.

McNally, David↗

NASA NTRS1999

Tropical Rainfall Measuring Mission

Tropical rainfall affects the lives and economics of a majority of the Earth's population. Tropical rain systems, such as hurricanes, typhoons, and monsoons, are crucial to sustaining the livelihoods of those living in the tropics. Excess rainfall can cause floods and great property and crop damage, whereas too little rainfall can cause drought and crop failure. The latent heat release during the process of precipitation is a major source of energy that drives the atmospheric circulation. This latent heat can intensify weather systems, affecting weather thousands of kilometers away, thus making tropical rainfall an important indicator of atmospheric circulation and short-term climate change. Tropical forests and the underlying soils are major sources of many of the atmosphere's trace constituents. Together, the forests and the atmosphere act as a water-energy regulating system. Most of the rainfall is returned to the atmosphere through evaporation and transpiration, and the atmospheric trace constituents take part in the recycling process. Hence, the hydrological cycle provides a direct link between tropical rainfall and the global cycles of carbon, nitrogen, and sulfur, all important trace materials for the Earth's system. Because rainfall is such an important component in the interactions between the ocean, atmosphere, land, and the biosphere, accurate measurements of rainfall are crucial to understanding the workings of the Earth-atmosphere system. The large spatial and temporal variability of rainfall systems, however, poses a major challenge to estimating global rainfall. So far, there has been a lack of rain gauge networks, especially over the oceans, which points to satellite measurement as the only means by which global observation of rainfall can be made. The Tropical Rainfall Measuring Mission (TRMM), jointly sponsored by the National Aeronautics and Space Administration (NASA) of the United States and the National Space Development Agency (NASDA) of Japan, provides visible, infrared, and microwave observations of tropical and subtropical rain systems.The satellite observations are complemented by ground radar and rain gauge measurements to validate satellite rain estimation techniques. Goddard Space Flight Center's involvement includes the observatory, four instruments, integration and testing of the observatory, data processing and distribution, and satellite operations. TRMM has a design lifetime of three years. Data generated from TRMM and archived at the GDAAC are useful not only for hydrologists, atmospheric scientists, and climatologists, but also for the health community studying infectious diseases, the ocean research community, and the agricultural community.

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NASA NTRS1991

Measurements and mechanisms of localized aqueous corrosion in aluminum-lithium-copper alloys

Summary information is included for electrochemical aspects of stress corrosion cracking in alloy 2090 and an introduction to the work to be initiated on the new X2095 (Weldalite) alloy system. Stress corrosion cracking (SCC) was studied in both S-T and L-T orientations in alloy 2090. A constant load TTF test was performed in several environments with a potentiostatically applied potential. In the same environments the electrochemical behavior of phases found along subgrain boundaries was assessed. It was found that rapid failure due to SCC occurred when the following criteria was met: E(sub BR,T1) is less than E(sub applied) is less than E(sub Br, matrix phase). Although the L-T orientation is usually considered more resistant to SCC, failures in this orientation occurred when the stated criteria was met. This may be due to the relatively isotropic geometry of the subgrains which measure approximately 12 to 25 microns in diameters. Initial studies of alloy X2095 includes electrochemical characterization of three compositional variations each at three temperatures. The role of T(sub 1) dissolution in SCC behavior is addressed using techniques similar to those used in the research of 2090 described. SCC susceptibility is also studied using alternate immersion facilities at Reynolds Metals Corporation. Pitting is investigated in terms of stability, role of precipitate phases and constituent particles, and as initiation sites for SCC. In all research endeavors, attempts are made to link electrochemistry to microstructure. Previous work on 2090 provides a convenient basis for comparison since both alloys contain T(sub 1) precipitates but with different distributions. In 2090 T(sub 1) forms preferentially on subgrain boundaries whereas in X2095 the microstructure appears to be more homogeneous with finer T(sub 1) particles. Another point for comparison is the delta prime strengthening phase found in 2090 but absent in X2095.

Wall, Douglas↗

NASA NTRS2002

Comparative Fatigue Lives of Rubber and PVC Wiper Cylindrical Coatings

Three coating materials for rotating cylindrical-coated wiping rollers were fatigue tested in 2 Intaglio printing presses. The coatings were a hard, cross-linked, plasticized PVC thermoset (P-series); a plasticized PVC (A-series); and a hard, nitryl rubber (R-series). Both 2- and 3-parameter Weibull analyses as well as a cost-benefit analysis were performed. The mean value of life for the R-series coating is 24 and 9 times longer than the P- and A-series coatings, respectively. Both the cost and replacement rate for the R-series coating was significantly less than those for the P- and A-series coatings. At a very high probability of survival the R-series coating is approximately 2 and 6 times the lives of the P- and A-series, respectively, before the first failure occurs. Where all coatings are run to failure, using the mean (life) time between removal (MTBR) for each coating to calculate the number of replacements and costs provides qualitatively similar results to those using a Weibull analysis.

Vlcek, Brian L.↗

NASA NTRS2008

Root Source Analysis/ValuStream[Trade Mark] - A Methodology for Identifying and Managing Risks

Root Source Analysis (RoSA) is a systems engineering methodology that has been developed at NASA over the past five years. It is designed to reduce costs, schedule, and technical risks by systematically examining critical assumptions and the state of the knowledge needed to bring to fruition the products that satisfy mission-driven requirements, as defined for each element of the Work (or Product) Breakdown Structure (WBS or PBS). This methodology is sometimes referred to as the ValuStream method, as inherent in the process is the linking and prioritizing of uncertainties arising from knowledge shortfalls directly to the customer's mission driven requirements. RoSA and ValuStream are synonymous terms. RoSA is not simply an alternate or improved method for identifying risks. It represents a paradigm shift. The emphasis is placed on identifying very specific knowledge shortfalls and assumptions that are the root sources of the risk (the why), rather than on assessing the WBS product(s) themselves (the what). In so doing RoSA looks forward to anticipate, identify, and prioritize knowledge shortfalls and assumptions that are likely to create significant uncertainties/ risks (as compared to Root Cause Analysis, which is most often used to look back to discover what was not known, or was assumed, that caused the failure). Experience indicates that RoSA, with its primary focus on assumptions and the state of the underlying knowledge needed to define, design, build, verify, and operate the products, can identify critical risks that historically have been missed by the usual approaches (i.e., design review process and classical risk identification methods). Further, the methodology answers four critical questions for decision makers and risk managers: 1. What s been included? 2. What's been left out? 3. How has it been validated? 4. Has the real source of the uncertainty/ risk been identified, i.e., is the perceived problem the real problem? Users of the RoSA methodology have characterized it as a true bottoms up risk assessment.

Brown, Richard Lee↗

NASA NTRS2012

NAND Flash Qualification Guideline

Better performing Forward Error Correction on the forward link along with adequate power in the data open an uplink operations trade space that enable missions to: Command to greater distances in deep space (increased uplink margin). Increase the size of the payload data (latency may be a factor). Provides space for the security header/trailer of the CCSDS Space Data Link Security Protocol. Note: These higher rates could be used for relief of emergency communication margins/rates and not limited to improving top-end rate performance. A higher performance uplink could also reduce the requirements on flight emergency antenna size and/or the performance required from ground stations. Use of a selective repeat ARQ protocol may increase the uplink design requirements but the resultant development is deemed acceptable, due the factor of 4 to 8 potential increase in uplink data rate.

Floating Gate Memory↗

NASA NTRS2019

Completion of the Long Duration Wear Test of the NASA HERMeS Hall Thruster

The NASA Hall Effect Rocket with Magnetic Shielding (HERMeS) 12.5-kW Hall thruster has been the subject of extensive technology maturation by NASA GRC and JPL in preparation for development into a flight propulsion system. As part of this effort, a series of wear tests have been conducted to identify erosion phenomena and the accompanying failure modes as well as to validate service-life models for magnetically-shielded thrusters. This work presents a summary of the results obtained during the Long Duration Wear Test (LDWT), which was the third in this wear test series. The LDWT accumulated approximately 3,570 hours of operation and had the overall goal to identify and correct design or facility issues prior to the flight qualification campaign. Thruster performance, stability, and plume properties were invariant throughout the duration of the LDWT and consistent with measurements acquired during previous HERMeS performance and wear characterizations. Average erosion rates of a carbon-carbon composite pole cover were found to match those measured with graphite to within the empirical uncertainty while the previously observed time-dependence of pole cover erosion rates was linked to changes in pole cover roughness. Azimuthal variations in keeper wear rate were observed including deposition on one of the azimuthal-facing sides of the keeper mask. This strongly suggests the presence of an azimuthal component in the process driving keeper erosion.

Frieman, Jason D.↗

NASA NTRS2019

Completion of the Long Duration Wear Test of the NASA HERMeS Hall Thruster

Frieman, Jason D.↗