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At least 1,027 records · Page 57

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NASA NTRS2016

Post-Test Inspection of NASA's Evolutionary Xenon Thruster Long Duration Test Hardware: Ion Optics

A Long Duration Test (LDT) was initiated in June 2005 as a part of NASA's Evolutionary Xenon Thruster (NEXT) service life validation approach. Testing was voluntarily terminated in February 2014, with the thruster accumulating 51,184 hours of operation, processing 918 kg of xenon propellant, and delivering 35.5 MN-s of total impulse. The post-test inspection objectives for the ion optics were derived from the original NEXT LDT test objectives, such as service life model validation, and expanded to encompass other goals that included verification of in situ measurements, test issue root causes, and past design changes. The ion optics cold grid gap had decreased only by an average of 7% of pretest center grid gap, so efforts to stabilize NEXT grid gap were largely successful. The upstream screen grid surface exhibited a chamfered erosion pattern. Screen grid thicknesses were ≥ 86% of the estimated pretest thickness, indicating that the screen grid has substantial service life remaining. Deposition was found on the screen aperture walls and downstream surfaces that was primarily composed of grid material and back-sputtered carbon, and this deposition likely caused the minor decreases in screen grid ion transparency during the test. Groove depths had eroded through up to 35% of the accelerator grid thickness. Minimum accelerator aperture diameters increased only by about 5-7% of the pretest values and downstream surface diameters increased by about 24-33% of the pretest diameters. These results suggest that increasing the accelerator aperture diameters, improving manufacturing tolerances, and masking down the perforated diameter to 36 cm were successful in reducing the degree of accelerator aperture erosion at larger radii.

Ion Thruster↗

NASA NTRS2016

Post-Test Inspection of Nasa's Evolutionary Xenon Thruster Long Duration Test Hardware: Ion Optics

A Long Duration Test (LDT) was initiated in June 2005 as a part of NASAs Evolutionary Xenon Thruster (NEXT) service life validation approach. Testing was voluntarily terminated in February 2014, with the thruster accumulating 51,184 hours of operation, processing 918 kg of xenon propellant, and delivering 35.5 MN-s of total impulse. This presentation will present the post-test inspection results to date for the thrusters ion optics.

Ion Engine↗

NASA NTRS2016

Post-Test Inspection of NASA's Evolutionary Xenon Thruster Long-Duration Test Hardware: Discharge Chamber

NASAs Evolutionary Xenon Thruster (NEXT) Long-Duration Test (LDT) is part of the comprehensive service life assessment of the NEXT thruster. The test was voluntarily terminated in April 2014 after accumulating 51,184 hours of high voltage operation, processing 918 kg of xenon, and delivering 35.5 MN-s of total impulse. This presentation covers the post-test inspection of the thruster hardware, in particular of the discharge chamber and other miscellaneous components such as propellant isolators and electrical cabling.

Ion Thrusters↗

NASA NTRS2017

Development and Testing of a Friction-Based Post-Installable Fiber-Optic Monitoring System for Subsea Applications

This paper presents the design and development of a friction-based coupling device for a fiber-optic monitoring system capable of measuring pressure, strain, and temperature that can be deployed on existing subsea structures. A summary is provided of the design concept, prototype development, prototype performance testing, and subsequent design refinements of the device. The results of laboratory testing of the first prototype performed at the National Aeronautics and Space Administration (NASA) Johnson Space Center (JSC) are also included. Limitations of the initial concept were identified during testing and future design improvements were proposed and later implemented. These new features enhance the coupling of the sensor device and improve the monitoring system measurement capabilities. A major challenge of a post-installed instrumentation monitoring system is to ensure adequate coupling between the instruments and the structure of interest for reliable measurements. Friction-based devices have the potential to overcome coupling limitations caused by marine growth and soil contamination on flowlines, risers, and other subsea structures. The work described in this paper investigates the design and test of a friction-based coupling device (herein referred to as a friction clamp) which is suitable for pipelines and structures that are suspended in the water column as well as for those that are resting on the seabed. The monitoring elements consist of fiberoptic sensors that are bonded to a stainless steel clamshell assembly with a high-friction surface coating. The friction clamp incorporates a single hinge design to facilitate installation of the clamp and dual rows of opposing fasteners to distribute the clamping force along the structure. The friction clamp can be modified to be installed by commercial divers in shallow depths or by remotely operated vehicles in deep-water applications. NASA-JSC was involved in the selection and testing of the friction coating, and in the design and testing of the prototype clamp device. Four-inch diameter and eight-inch diameter sub-scale friction clamp prototypes were built and tested to evaluate the strain measuring capabilities of the design under different loading scenarios. The testing revealed some limitations of the initial design concept, and subsequent refinements were explored to improve the measurement performance of the system. This study was part of a collaboration between NASA-JSC and Astro Technology Inc. within a study called Clear Gulf. The primary objective of the Clear Gulf study is to develop advanced instrumentation technologies that will improve operational safety and reduce the risk of hydrocarbon spillage. NASA provided unique insights, expansive test facilities, and technical expertise to advance technologies that will benefit the environment, the public, and commercial industries.

Bentley, Nicole L.↗

NASA NTRS2017

Estimation of Reconnection Flux Using Post-Eruption Arcades and Its Relevance to Magnetic Clouds at 1 AU

We report on a new method to compute the flare reconnection (RC) flux from post-eruption arcades (PEAs) and the underlying photospheric magnetic fields. In previous works, the RC flux has been computed using the cumulative flare ribbon area. Here we obtain the RC flux as the flux in half of the area underlying the PEA in EUV imaged after the flare maximum. We apply this method to a set of 21 eruptions that originated near the solar disk center in Solar Cycle 23. We find that the RC flux from the arcade method ((Phi)rA) has excellent agreement with the flux from the flare-ribbon method ((Phi)rR) according to (Phi)rA = 1.24((Phi)rR)(sup 0.99). We also find (Phi)rA to be correlated with the poloidal flux ((Phi)P) of the associated magnetic cloud at 1 AU: (Phi)P = 1.20((Phi)rA)(sup 0.85). This relation is nearly identical to that obtained by Qiu et al. (Astrophys. J. 659, 758, 2007) using a set of only 9 eruptions. Our result supports the idea that flare reconnection results in the formation of the flux rope and PEA as a common process.

Gopalswamy, N.↗

NASA NTRS2017

Methane Post-Processing and Hydrogen Separation for Spacecraft Oxygen Loop Closure

State-of-the-art life support oxygen recovery technology on the International Space Station is based on the Sabatier reaction where only about half of the oxygen required for the crew is recovered from metabolic carbon dioxide (CO2). The Sabatier reaction produces water as the primary product and methane as a byproduct. Oxygen recovery is constrained by both the limited availability of reactant hydrogen from water electrolysis and Sabatier methane (CH4) being vented as a waste product resulting in a continuous loss of reactant hydrogen. Post-processing methane with the Plasma Pyrolysis Assembly (PPA) to recover this hydrogen has the potential to substantially increase oxygen recovery and thus dramatically reduce the logistical challenges associated with oxygen resupply. The PPA decomposes methane into predominantly hydrogen and acetylene. A purification system is necessary to purify hydrogen before it is recycled back to the Sabatier reactor. Testing and evaluation of acetylene removal systems and PPA system architectures are presented and discussed.

Greenwood, Zachary W.↗

NASA NTRS2017

Improvement of Automated POST Case Success Rate Using Support Vector Machines

During early conceptual design of complex systems, concept down selection can have a large impact upon program life-cycle cost. Therefore, any concepts selected during early design will inherently commit program costs and affect the overall probability of program success. For this reason it is important to consider as large a design space as possible in order to better inform the down selection process. For conceptual design of launch vehicles, trajectory analysis and optimization often presents the largest obstacle to evaluating large trade spaces. This is due to the sensitivity of the trajectory discipline to changes in all other aspects of the vehicle design. Small deltas in the performance of other subsystems can result in relatively large fluctuations in the ascent trajectory because the solution space is non-linear and multi-modal. In order to help capture large design spaces for new launch vehicles, the authors have performed previous work seeking to automate the execution of the industry standard tool, Program to Optimize Simulated Trajectories (POST). This work initially focused on implementation of analyst heuristics to enable closure of cases in an automated fashion, with the goal of applying the concepts of design of experiments (DOE) and surrogate modeling to enable near instantaneous throughput of vehicle cases.3 As noted in [4] work was then completed to improve the DOE process by utilizing a graph theory based approach to connect similar design points.

Zwack, Mathew R.↗

NASA NTRS2017

Evidence for the Presence of Hn-PAHs in Post AGB Stars

Polycyclic aromatic hydrocarbons (PAHs) are believed to be ubiquitous in space therefore represent an important class of molecules for the field of astrochemistry. PAHs are relatively stable under interstellar conditions, account for a significant fraction of the known Universe's molecular carbon inventory, and are believed responsible for numerous telltale interstellar infrared emission bands. PAHs can be subdivided into numerous classes, one of which is Hydrogenated PAHs (Hn-PAHs). Hn-PAHs are multi-ringed partially aromatic compounds with excess hydrogenation, leading to a partial disruption of the aromatic system. The infrared spectra of these compounds produce telltale signatures that make them distinct from ordinary aromatic or aliphatic molecules (or a mixture of both). Hn-PAHs may be an important subclass of PAHs that could explain the spectra of some astronomical objects with anomalously large 3.4 micron features. The 3.4 micron feature observed in these objects may be associated with the aliphatic C-H stretching vibrations of the excess hydrogen. If this presumption is correct, we also expect to observe methylene scissoring modes at 6.9 microns. We have recently conducted a series of follow-up observations to compliment our laboratory experiments into the properties of Hn-PAHs. Here we present our laboratory and observational results in support of the hypothesis that Hn-PAHs are a viable candidate molecule as the emission source for numerous post-asymptotic giant branch objects with abnormally large 3.4 micron features.

SOFIA↗

NASA NTRS2017

Update of the NEXT Ion Thruster Service Life Assessment with Post-Test Correlation to the Long Duration Test

The service life assessment for NASA's Evolutionary Xenon Thruster is updated to incorporate the results from the successful and voluntarily early completion of the 51,184 hour long duration test which demonstrated 918 kg of total xenon throughput. The results of the numerous post-test investigations including destructive interrogations have been assessed against all of the critical known and suspected failure mechanisms to update the life and throughput expectations for each major component. Analysis results of two of the most acute failure mechanisms, namely pit-and-groove erosion and aperture enlargement of the accelerator grid, are not updated in this work but will be published at a future time after analysis completion.

ion engines↗

NASA NTRS2018

Soil Moisture Active/Passive (SMAP) L-Band Microwave Radiometer Post-Launch Calibration Upgrade

Current performance and existing problems in SMAP radiometer L1B_TB version 3 data product are described. The post-launch calibration algorithm has been updated by calibrating the three calibration parameters (the equivalent noise temperature of the noise diode, the offset of the reference load, and the antenna gain) jointly by using the global ocean and CS with both 110o and 180o pitch maneuvers after the reflector emissivity is calibrated. The results show that both calibration drift during eclipse season and bias over CS are removed. The RMSDs of the calibration drift over both the global ocean and CS are less than 0.1 K, and the goals of the calibration algorithm upgrade are achieved for coming L1B_TB version 4 data release.

Validation↗

NASA NTRS2018

Asymmetric Post-Magma Ocean Crust-Building on the Lunar Nearside

Mg-suite is a series of ancient plutonic rocks from the lunar crust with ages and com-positions indicating that they represent the first post-differentiation crust-building magmatism [1, 2]. Sam-ples of Mg-suite materials were found at every Apollo landing site except 11 and all exhibit geochemical characteristics indicating the involvement of KREEP in their petrogenesis [3-5]. This has led to the sugges-tion that the KREEP reservoir under the nearside was responsible for Mg-suite magmatism [e.g., 5, 6]. The lack of readily identifiable Mg-suite rocks in meteoritic regolith breccias sourced from outside the Procellarum KREEP Terrane (PKT) seemingly supports this interpretation.

Elardo, S. M.↗

NASA NTRS2018

Assessment of Volatile Depletion Mechanisms for the Moon - Pre-Cursors, Giant Impact, Core Formation, Post-Impact Loss

The volatile element depletions in the Moon have been recognized for decades. Multiple explanations have been debated, and arguments have become more quantitative, in large part due to new elemental partitioning and isotopic data. Depletions in pre-cursor materials and due to post-accretion degassing have been evaluated using isotopic data. Partitioning of many volatile elements into metallic cores can now be evaluated for many volatile siderophile elements (VSE). Here is presented an evaluation of the role of core formation for 12 volatile siderophile elements for which partitioning data is now available. Examination of all 12 elements at once allows recognition of general trends, without undue focus on one element. Ga, Ge, Zn, Sn, As, Sb, Cd, Ag, Bi, P, In, Cu are all moderately to highly volatile, and will be discussed in their order of volatility as gauged by their 50 percent condensation temperature.

Righter, K.↗

NASA NTRS2018

Reducing Hazards of Propulsive Secondary Payloads by Implementing a Post Launch Pressurization System

Propulsion systems on SmallSats and CubeSats are becoming more common as launch vehicles like SLS begin providing rideshares to destinations beyond low earth orbit. While these spacecraft are a solution to achieve advanced science objectives at lower cost, they are still subject to the same rigorous standards as other larger spacecraft, such as NASA STD-5019, due to the high pressures within their propulsion systems at launch. A Post Launch Pressurization System would allow a spacecraft to be launched at low pressure, then be pressurized through the controlled chemical decomposition of a solid reactant after the spacecraft is jettisoned from the launch vehicle. This increases the safety of the secondary spacecraft, and effectively mitigates risks to the launch vehicle and other payloads.

Perry, McKynzie↗

NASA NTRS2018

WFIRST CGI Integral Field Spectrograph Performance and Post-Processing in the OS6 Observing Scenario

The WFIRST coronagraph instrument (CGI) will have an integral field spectrograph (IFS) backend to disperse the entire field of view at once and obtain spatially-resolved, low-resolution spectra of the speckles and science scene. The IFS will be key to understanding the spectral nature of the speckles, obtain science spectra of planets and disks, and will be used for broadband wavefront control. In order to characterize, predict, and optimize the performance of the instrument, we present a detailed model of the IFS in the context of the new OS6 observing scenario. The simulation includes spatial, spectral, and temporal variations of the speckle field on the IFS detector plane, which allows us to explore several post-processing methods and assess what gains can be expected. The simulator includes the latest models of the detector behavior when operating in photon-counting mode.

WFIRST coronagraph instrument (CGI)↗

NASA NTRS2019

Post-Test Microstructural Analysis of Particle Impact-Tested Wrought Inconel, Additively Manufactured Inconel and Wrought Monel Targets

Particle impact testing in high pressure oxygen was performed to evaluate ignition susceptibility of Inconel 718 and Monel 400. Sapphire particles (1.5-mm diameter) under high pressure oxygen, travelling at hypersonic speeds, made impact with metal targets, resulting in surface indentations. This report details the post-test characterization of impact craters observed on three metallic target samples: wrought nickel-based superalloy Inconel 718 (IN718), additively manufactured Inconel 718 (AM-IN718) and nickel-copper alloy, Monel 400.

Ochoa, Ngozi C.↗

NASA NTRS2020

Temporal Changes in Astronauts’ Muscle and Cardiorespiratory Physiology Pre-, In-, and Post-Spaceflight

NASA’s vision for future exploration missions depends on the ability to protect astronauts’ health and safety for performance of Extravehicular Activity (EVA), and to allow astronauts to safely egress from vehicles in a variety of landing scenarios (e.g. water landing upon return to Earth and undefined planetary/lunar landings). Prolonged exposure to spaceflight results in diminished tolerance to prolonged physical activity, decreased cardiac and sensorimotor function, and loss of bone mineral density, muscle mass, and muscle strength. For over 50 years exercise has been the primary countermeasure against these physiologic decrements during spaceflight, and while the resulting protection is adequate for ISS missions (i.e., Soyuz landing, microgravity EVAs), there is little information regarding time-course changes in muscle and aerobic performance. As spaceflight progresses towards longer exploration missions and vehicles with less robust exercise capabilities compared to ISS, countermeasures will need to be combined and optimized to protect crew health and performance across all organ systems over the course of exploration missions up to 3 years in duration. This will require a more detailed understanding of the dynamic effects of spaceflight on human performance. Thus, the focus of this study is quantifying decrements in physical performance over different mission durations, and to provide detailed information on the physiological rational for “why” and “when” observed changes in performance occur. The research proposed will temporally profile changes in astronauts’ cardiorespiratory fitness, muscle mass, strength, and endurance over spaceflight missions of 2 months, 6 months, and up to 1 year in duration. Additionally, an extrapolation model will provide predictions for changes associated with exploration missions 2-3 years in duration. To accomplish these objectives astronauts will be asked to participate in pre, in, post-flight measurement of muscle performance, muscle size, cardiorespiratory fitness and submaximal performance capabilities, as well as non-invasive assessment of cerebral and muscle oxygenation and perfusion (Table 1). Additionally, ambulatory and in-flight exercise, nutrition, and sleep will be monitored using a variety of commercial technologies and in-flight assessment tools. Significance: Our detailed testing protocol will provide valuable information for describing how and when spaceflight-induced muscle and aerobic based adaptations occur over the course of spaceflight missions up to and beyond 1 year. This information will be vital in the assessment as to whether humans can be physically ready for deep space exploration such as Mars missions with current technology, or if additional mitigation strategies are necessary.

Downs, M. E.↗

NASA NTRS2018

ASPIRE Flight Mechanics Modeling and Post Flight Analysis

The Advanced Supersonic Parachute Inflation Research and Experiment (ASPIRE) is a series of sounding rocket flights aimed at understanding the dynamics of supersonic parachutes that are used for Mars robotic applications. SR01 was the first sounding rocket flight of ASPIRE that occurred off the coast of Wallops Island, VA on Oct. 4, 2017 and showed the successful deployment and inflation of a Mars Science Laboratory built-to- print parachute in flight conditions similar to the 2012 Mars Science Laboratory (MSL) mission. SR02 was the second sounding rocket flight that also occurred off the coast of Wallops Island on March 31, 2018 and showcased the successful deployment and inflation of a new strengthened parachute being considered for the Mars 2020 mission at fifty percent higher dynamic pressure than observed on MSL. Prior to both flights, a multi-body flight dynamics simulation was developed to predict the parachute dynamics and was used, in conjunction with other tools, to target Mars-relevant flight conditions. After each flight, the reconstructed trajectory was used to validate the pre-flight dynamics simulation and recommend changes to improve predictions for future flights planned for the ASPIRE pro- gram. This paper describes the flight mechanics simulation and the post flight reconciliation process used to validate the flight models.

Dutta, Soumyo↗

NASA NTRSDate not supplied

Progressive Damage Analysis of Post-Buckled Stiffened Panels under Static Compressive Loading

The validation of progressive damage analysis methods requires experimental data that captures the initiation of damage, its evolution with continued loading, and the morphology of damage throughout its evolution. In support of the NASA Advanced Composites Project, several validation specimens of increasing complexity have been tested and characterized in order to provide the data required to assess the capabilities of several progressive damage analysis methods for fiber-reinforced composite materials. The analytical capabilities of interest for this validation program include networks of interacting matrix cracks and delaminations in post-buckled stiffened structures. A series of single stringer compression specimens was tested and characterized at NASA Langley Research Center. The experimental data from these tests are compared with progressive damage finite element analysis results. Test/analysis comparisons are made in terms of load/displacement histories, damage morphology, and damage size versus load metrics.

Frank A Leone↗