Challenges and Methods in Testing the Remote Agent Planner
The Remote Agent Experiment (RAX) on the Deep Space 1 (DS1) mission was the first time that an artificially intelligent agent controlled a NASA spacecraft.
planning↗
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Challenges and Methods in Testing the Remote Agent Planner
The Remote Agent Experiment (RAX) on the Deep Space 1 (DS1) mission was the first time that an artificially intelligent agent controlled a NASA spacecraft.
planning↗
Evaluation of Conservatism in Low Frequency Vibration Test Control
Aerospace structures are typically qualified for low frequency flight environments by using a swept-sine vibration test method. However, this ground testing has a tendency to produce substantial overtesting at certain frequencies. This paper presents an evaluation of the response conservatism present with a typical swept-sine and two transient vibration tests when applied to a typical spacecraft component. The absolute conservatism between a typical launch transient response and the test environment responses is measured using alternative characterizations of transient vibrations previously used in shock testing. The characterizations used include the Shock Intensity Spectrum, Shock Response Spectrum, Acceleration Root Mean Square in both frequency and time domains, and Ranked Peaks. Control of the test/flight conservatism is shown to be possible through the overtest factor (OTF) parameter.
Conservatism↗
SCIFLI HORIS Windowpane Optical Analysis
This NASA Technical Memorandum summarizes windowpane optical analyses for the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification and Security Regolith Explorer) mission [1] supported by the SCIFLI (Scientifically Calibrated In-Flight Imagery) team [2] at NASA Langley Research Center (NASA LaRC). The SCIFLI team led a NASA multi-center team in characterization of fused silica (FS) and anti-reflective coated (AR-coated) sapphire materials for use as aircraft windowpanes. These materials were needed for the Hypervelocity OSIRIS-REx Reentry Imaging & Spectroscopy (HORIS) mission and were tested to generate performance parameters relevant to the flight environment. Some of the assessed parameters included optical quality, transmittance, reflectance, color balance, birefringence, transmitted wavefront error, wedge, and haziness of the windows. In order to evaluate the material characteristics in a uniform manner, several criteria were held constant. For example, the physical dimensions of the test articles were held constant (i.e., 17-inch diameter aircraft windowpane and 2-inch diameter witness samples). In this way, the comparison of test results from one material specimen to another was invariant with regard to the manner in which the tests were conducted. This also reduced the variability in how the data were reported. As a result, the results shown in this report, including test data generated by NASA can be used for windowpane material evaluation and future material design trades. Window designers can use the data and the testing method along with the testing matrices to efficiently match material performance to their design and mission objectives and requirements. Standardized testing methodologies and data reduction procedures are described in this report. Unless otherwise noted in the data itself, all the windowpane materials were tested in order to characterize their performance for the HORIS mission. One appendix has been included in this report. These include detailed wavefront interferograms of transmitted wavefront error and optical wedge used in the generation of aggregated material performance.
SCIFLI↗
Submerged Fatigue Testing of Marine Energy Advanced Materials: Preprint
Marine energy structures are typically made of advanced composite materials and are subjected to extreme ocean environments in service. In extreme ocean environments, seawater currents and waves load structures repeatedly, which cause two environmental conditions: water intrusion and mechanical fatigue. In prior research, the two environmental conditions were applied sequentially, where composite specimens were aged and then mechanically tested. To understand the combined effects of dynamic loading and water intrusion on composite materials, the present study involves the static and fatigue four-point bend testing of composite coupons in a water tank. The water tank was designed and built to fit either a 100 kN or a 250 kN load frame. Flexural strength value, cycles to failure, and failure mode results from submerged fatigue testing will be used to inform marine energy structure designs. The coupon-scale test method will be used to scale up to and inform methods for subsequent subcomponent testing and standards development. The benefits of designing marine energy structures to informed standards are decreased lifetime costs and increased reliability and energy production, ultimately leading to a sustainable and low-carbon energy system.
composite materials↗
Submerged Fatigue Testing of Marine Energy Advanced Materials
Marine energy structures are typically made of advanced composite materials and are subjected to extreme ocean environments in service. In extreme ocean environments, seawater currents and waves load structures repeatedly, which cause two environmental conditions: water intrusion and mechanical fatigue. In prior research, the two environmental conditions were applied sequentially, where composite specimens were aged and then mechanically tested. To understand the combined effects of dynamic loading and water intrusion on composite materials, the present study involves the static and fatigue four-point bend testing of composite coupons in a water tank. The water tank was designed and built to fit either a 100 kN or a 250 kN load frame. Flexural strength value, cycles to failure, and failure mode results from submerged fatigue testing will be used to inform marine energy structure designs. The coupon-scale test method will be used to scale up to and inform methods for subsequent subcomponent testing and standards development. The benefits of designing marine energy structures to informed standards are decreased lifetime costs and increased reliability and energy production, ultimately leading to a sustainable and low-carbon energy system.
composite materials↗
Sizing Single Cantilever Beam Specimens for Characterizing Facesheet/Core Peel Debonding in Sandwich Structure
This paper details part of an effort focused on the development of a standardized facesheet/core peel debonding test procedure. The purpose of the test is to characterize facesheet/core peel in sandwich structure, accomplished through the measurement of the critical strain energy release rate associated with the debonding process. The specific test method selected for the standardized test procedure utilizes a single cantilever beam (SCB) specimen configuration. The objective of the current work is to develop a method for establishing SCB specimen dimensions. This is achieved by imposing specific limitations on specimen dimensions, with the objectives of promoting a linear elastic specimen response, and simplifying the data reduction method required for computing the critical strain energy release rate associated with debonding. The sizing method is also designed to be suitable for incorporation into a standardized test protocol. Preliminary application of the resulting sizing method yields practical specimen dimensions.
Ratcliffe, James G.↗
Dynamic Stability Test Technique for Blunt Bodies in a Magnetic Suspension and Balance System
Techniques for the measurement of subsonic dynamic stability derivatives of blunt-body re-entry capsules are being developed using a Magnetic Suspension and Balance System at NASA Langley Research Center. The measured aerodynamics of a 45-degree sphere-cone similar to configurations being considered for Mars Sample Return Earth Entry Vehicle are reported. A novel test method has been developed where forced oscillatory translation of a test article is used to excite yaw attitude oscillations. The forced motion is then halted to observe free-to-oscillate behavior of the test article. Parameter identification methods are used to extract drag as well as static and dynamic yawing moment stability characteristics from the measured forces and observed attitude histories. This combination of forced excitation followed by free-to-oscillate dynamics is a repeatable method to produce test article attitude histories that can be used to measure aerodynamic characteristics.
Entry Systems Modeling↗
Dynamic Stability Test Technique for Blunt Bodies in a Magnetic Suspension and Balance System
Techniques for the measurement of subsonic dynamic stability derivatives of blunt-body re-entry capsules are being developed using a Magnetic Suspension and Balance System at NASA Langley Research Center. The measured aerodynamics of a 45-degree sphere-cone similar to configurations being considered for Mars Sample Return Earth Entry Vehicle are reported. A novel test method has been developed where forced oscillatory translation of a test article is used to excite yaw attitude oscillations. The forced motion is then halted to observe free-to-oscillate behavior of the test article. Parameter identification methods are used to extract drag as well as static and dynamic yawing moment stability characteristics from the measured forces and observed attitude histories. This combination of forced excitation followed by free-to-oscillate dynamics is a repeatable method to produce test article attitude histories that can be used to measure aerodynamic characteristics.
Entry Systems Modeling↗
Buckling analysis and test correlation of high temperature structural panels
This paper focuses on the design, analysis, and test of a high temperature structural panel, constructed of Ti-6-4, subjected to a variety of thermal and mechanical load conditions. A follow-on panel, constructed of TMC, is also discussed in less detail. The design constraints and test set-up are discussed, as well as the test methods that were used: the grid shadow moire method and a single gage force stiffness method. The agreement between the test data and analysis for this test program provides confidence in the methods that are currently being used to design structures for hypersonic vehicles. The agreement also suggests that postbuckled strength may potentially be used to reduce the vehicle weight.
Teare, Wendy P.↗
Development of a transfer function method for dynamic stability measurement
Flutter testing method based on transfer function measurements is developed. The error statistics of several dynamic stability measurement methods are reviewed. It is shown that the transfer function measurement controls the error level by averaging the data and correlating the input and output. The method also gives a direct estimate of the error in the response measurement. An algorithm is developed for obtaining the natural frequency and damping ratio of low damped modes of the system, using integrals of the transfer function in the vicinity of a resonant peak. Guidelines are given for selecting the parameters in the transfer function measurement. Finally, the dynamic stability measurement technique is applied to data from a wind tunnel test of a proprotor and wing model.
Johnson, W.↗
Detectability of Varied Hybridization Scenarios Using Genome-Scale Hybrid Detection Methods
Hybridization events complicate the accurate reconstruction of phylogenies, as they lead to patterns of genetic heritability that are unexpected under traditional, bifurcating models of species trees. This phenomenon has led to the development of methods to infer these varied hybridization events, both methods that reconstruct networks directly, as well as summary methods that predict individual hybridization events from a subset of taxa. However, a lack of empirical comparisons between methods – especially those pertaining to large networks with varied hybridization scenarios – hinders their practical use. Here, we provide a comprehensive review of popular summary methods: TICR, MSCquartets, HyDe, Patterson’s D-Statistic (ABBA-BABA), D3, and Dp. TICR and MSCquartets are based on quartet concordance factors gathered from gene tree topologies and HyDe, Patterson’s D-Statistic, D3, and Dp use site pattern frequencies to identify hybridization events between sets of three taxa. We then use simulated data to address questions of method accuracy and ideal use scenarios by testing methods against complex networks which depict gene flow events that differ in depth (timing), quantity (single vs. multiple, overlapping hybridizations), and rate of gene flow (γ). We find that deeper or multiple hybridization events may introduce noise and weaken the signal of hybridization, leading to higher relative false negative rates across all methods. Despite some forms of hybridization eluding quartet-based detection methods, MSCquartets displays high precision in most scenarios. While HyDe results in high false negative rates when tested on hybridizations involving extinct or unsampled ghost lineages, HyDe is the only method able to identify the direction of hybridization, distinguishing the source parental lineages from recipient hybrid lineages. Lastly, we test the methods on a dataset of ultraconserved elements from the bee subfamily Nomiinae, finding possible hybridization events between clades which correspond to regions of poor support in the species tree estimated in a previous study.
Bjorner, Marianne B.↗
Buckling analysis and test correlation of hat stiffened panels for hypersonic vehicles
The paper discusses the design, analysis, and test of hat stiffened panels subjected to a variety of thermal and mechanical load conditions. The panels were designed using data from structural optimization computer codes and finite element analysis. Test methods included the grid shadow moire method and a single gage force stiffness method. The agreement between the test data and analysis provides confidence in the methods that are currently being used to design structures for hypersonic vehicles. The agreement also indicates that post buckled strength may potentially be used to reduce the vehicle weight.
Percy, Wendy C.↗
Corrosion Testing of Refractory inContact with Molten Glasses Designed for Waste Vitrification - VSL Touchpoint Matrix Glasses
It is known that the predictive life of the refractory ceramic liner of nuclear waste glass melters is conservative, as demonstrated by performance of these materials such as in the Defense Waste Processing Facility (DWPF). The motivation for this task is to maximize the useful life of the melters that will be operated at the Waste Treatment and Immobilization Plant (WTP), which will in turn minimize procurement and disposal costs and melter outage times, as well as to identify maximum loadings in the waste glass of those species that corrode melter components. This task was initiated jointly with Pacific Northwest National Laboratory (PNNL) with the objective to develop a methodology and model to enable more accurate prediction of refractory service life under prototypic conditions from laboratory-scale material corrosion tests. Refractory corrosion is generally reported as physical material loss, measured in units of distance (e.g., inch) or as physical material loss rate, measured in units of distance per time (e.g., inch/day). In post-operational melters, the refractory corrosion is measured directly, sometimes reported as corrosion depth. Crucible tests are used in the laboratory to accelerate the refractory corrosion to facilitate a meaningful measurement in a commensurate amount of time. Crucible tests are particularly useful in understanding refractory corrosion across a large glass composition space, where operational testing would be prohibitive. Some of the critical parameters that are known to influence refractory corrosion by molten glass in a crucible test are temperature, system redox, molten salt phases, glass chemistry, and test duration. The majority of data collected for Monofrax® K-3 (hereafter referred to as K-3) corrosion is from crucible tests, but a small amount comes directly from scaled and production melters. Crucible test data has been collected under varying conditions, whereas data collected from operational melters is relatively fewer and represents conditions specific to the melter campaign. The result is that the published data can be grouped and analyzed in multiple ways, not all of which are readily comparable. The Standard Test Method for Isothermal Corrosion Resistance of Refractories to Molten Glass (ASTM C621) outlines the general guidelines used across industry. That method describes a sealed, static test in which the surface area of the refractory coupon and the volume of glass are fixed. A significant portion of the crucible data pertaining to nuclear waste glasses has been collected in a modified configuration; the most notable differences being the surface area of the refractory coupon to volume of the glass and use of a method for bubbling the melt. To our knowledge, the influence of those parameters on the refractory corrosion has not been quantified. In this work, it was determined that static tests and bubbled tests would be performed. Savannah River National Laboratory (SRNL) was tasked with setting up and performing static testing while PNNL was tasked with setting up and performing bubbled testing. Initial activities were performed to establish laboratory methods that reproduce data comparable to existing data sets of K-3 refractory corrosion by low activity waste (LAW) and high-level waste (HLW) glass compositions. Later activities were focused on refining the test parameters to establish a standard test practice to be used between Laboratories and collecting additional data to be used in the enhanced waste glass model development. This document serves primarily to convey the refractory loss measurement results from corrosion testing of K-3 refractory with waste glass compositions developed for use in the WTP melters. The data will be used in the enhanced property/composition models being developed for waste glass vitrification and melter operations.
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
A Criterion to Control Nonlinear Error in the Mixed-Mode Bending Test
The mixed-mode bending test ha: been widely used to measure delamination toughness and was recently standardized by ASTM as Standard Test Method D6671-01. This simple test is a combination of the standard Mode I (opening) test and a Mode II (sliding) test. This test uses a unidirectional composite test specimen with an artificial delamination subjected to bending loads to characterize when a delamination will extend. When the displacements become large, the linear theory used to analyze the results of the test yields errors in the calcu1ated toughness values. The current standard places no limit on the specimen loading and therefore test data can be created using the standard that are significantly in error. A method of limiting the error that can be incurred in the calculated toughness values is needed. In this paper, nonlinear models of the MMB test are refined. One of the nonlinear models is then used to develop a simple criterion for prescribing conditions where thc nonlinear error will remain below 5%.
Reeder, James R.↗
Explosively actuated /pyromechanical/ devices for spacecraft applications
Explosively actuated device design criteria and test methods
EXPLOSIVE DEVICE↗
A Method of Partly Automated Testing of Software
A method of automated testing of software has been developed that provides an alternative to the conventional mostly manual approach for software testing. The method combines (1) automated generation of test cases on the basis of systematic exploration of the input domain of the software to be tested with (2) run-time analysis in which execution traces are monitored, verified against temporal-logic specifications, and analyzed by concurrency-error-detection algorithms. In this new method, the user only needs to provide the temporal logic specifications against which the software will be tested and the abstract description of the input domain.
Lowry, Mike↗
Monte Carlo Simulation of Sudden Death Bearing Testing
Monte Carlo simulations combined with sudden death testing were used to compare resultant bearing lives to the calculated hearing life and the cumulative test time and calendar time relative to sequential and censored sequential testing. A total of 30 960 virtual 50-mm bore deep-groove ball bearings were evaluated in 33 different sudden death test configurations comprising 36, 72, and 144 bearings each. Variations in both life and Weibull slope were a function of the number of bearings failed independent of the test method used and not the total number of bearings tested. Variation in L10 life as a function of number of bearings failed were similar to variations in lift obtained from sequentially failed real bearings and from Monte Carlo (virtual) testing of entire populations. Reductions up to 40 percent in bearing test time and calendar time can be achieved by testing to failure or the L(sub 50) life and terminating all testing when the last of the predetermined bearing failures has occurred. Sudden death testing is not a more efficient method to reduce bearing test time or calendar time when compared to censored sequential testing.
Vlcek, Brian L.↗