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NASA NTRS1978

Toxicity of pyrolysis products: Influence of experimental conditions - The MSTL/UT and NASA/JSC Procedures

Ten sample materials of various polymeric composition were evaluated for toxicity of pyrolysis products utilizing two significantly different experimental methods, the MSTL/UT and NASA/JSC Procedures. A comparison of the LD(50) values obtained by the two methods for these ten samples did not yield a significant correlation. However, when the samples were ranked in order of increasing toxicity by each method independently, a comparison of their rank order toxicity improved the correlation. Because of interlaboratory variations in pyrolysis/combustion test procedures, it is suggested a series of standard materials be adopted to facilitate interlaboratory comparisons of data on pyrolysis toxicity.

Lawrence, W. H.↗

NASA NTRS2003

Sensitivity and Calibration of Non-Destructive Evaluation Method That Uses Neural-Net Processing of Characteristic Fringe Patterns

This paper answers some performance and calibration questions about a non-destructive-evaluation (NDE) procedure that uses artificial neural networks to detect structural damage or other changes from sub-sampled characteristic patterns. The method shows increasing sensitivity as the number of sub-samples increases from 108 to 6912. The sensitivity of this robust NDE method is not affected by noisy excitations of the first vibration mode. A calibration procedure is proposed and demonstrated where the output of a trained net can be correlated with the outputs of the point sensors used for vibration testing. The calibration procedure is based on controlled changes of fastener torques. A heterodyne interferometer is used as a displacement sensor for a demonstration of the challenges to be handled in using standard point sensors for calibration.

Decker, Arthur J.↗

NASA NTRS2017

A Fast, Accurate and Sensitive GC-FID Method for the Analyses of Glycols in Water and Urine

Glycols, specifically ethylene glycol and 1,2-propanediol, are some of the major organic compounds found in the humidity condensate samples collected on the International Space Station. The current analytical method for glycols is a GC/MS method with direct sample injection. This method is simple and fast, but it is not very sensitive. Reporting limits for ethylene glycol and 1,2-propanediol are only 1 ppm. A much more sensitive GC/FID method was developed, in which glycols were derivatized with benzoyl chloride for 10 minutes before being extracted with hexane. Using 1,3-propanediol as an internal standard, the detection limits for the GC/FID method was determined to be 50 ppb and the analysis only takes 7 minutes. Data from the GC/MS and the new GC/FID methods shows excellent agreement with each other. Factors affecting the sensitivity, including sample volume, NaOH concentration and volume, volume of benzoyl chloride, reaction time and temperature, were investigated. Interferences during derivatization and possible method to reduce interferences were also investigated.

Kuo, C. Mike↗

NASA NTRS2012

Transmission Electron Microscopy (TEM) Sample Preparation of Si(1-x)Gex in c-Plane Sapphire Substrate

The National Aeronautics and Space Administration-invented X-ray diffraction (XRD) methods, including the total defect density measurement method and the spatial wafer mapping method, have confirmed super hetero epitaxy growth for rhombohedral single crystalline silicon germanium (Si1-xGex) on a c-plane sapphire substrate. However, the XRD method cannot observe the surface morphology or roughness because of the method s limited resolution. Therefore the authors used transmission electron microscopy (TEM) with samples prepared in two ways, the focused ion beam (FIB) method and the tripod method to study the structure between Si1-xGex and sapphire substrate and Si1?xGex itself. The sample preparation for TEM should be as fast as possible so that the sample should contain few or no artifacts induced by the preparation. The standard sample preparation method of mechanical polishing often requires a relatively long ion milling time (several hours), which increases the probability of inducing defects into the sample. The TEM sampling of the Si1-xGex on sapphire is also difficult because of the sapphire s high hardness and mechanical instability. The FIB method and the tripod method eliminate both problems when performing a cross-section TEM sampling of Si1-xGex on c-plane sapphire, which shows the surface morphology, the interface between film and substrate, and the crystal structure of the film. This paper explains the FIB sampling method and the tripod sampling method, and why sampling Si1-xGex, on a sapphire substrate with TEM, is necessary.

Kim, Hyun Jung↗

NASA NTRS1998

Basis Selection for Wavelet Regression

A wavelet basis selection procedure is presented for wavelet regression. Both the basis and the threshold are selected using cross-validation. The method includes the capability of incorporating prior knowledge on the smoothness (or shape of the basis functions) into the basis selection procedure. The results of the method are demonstrated on sampled functions widely used in the wavelet regression literature. The results of the method are contrasted with other published methods.

Wheeler, Kevin R.↗

NASA NTRS2016

Sampling for Soil Carbon Stock Assessment in Rocky Agricultural Soils

Coring methods commonly employed in soil organic C (SOC) stock assessment may not accurately capture soil rock fragment (RF) content or soil bulk density (rho (sub b)) in rocky agricultural soils, potentially biasing SOC stock estimates. Quantitative pits are considered less biased than coring methods but are invasive and often cost-prohibitive. We compared fixed-depth and mass-based estimates of SOC stocks (0.3-meters depth) for hammer, hydraulic push, and rotary coring methods relative to quantitative pits at four agricultural sites ranging in RF content from less than 0.01 to 0.24 cubic meters per cubic meter. Sampling costs were also compared. Coring methods significantly underestimated RF content at all rocky sites, but significant differences (p is less than 0.05) in SOC stocks between pits and corers were only found with the hammer method using the fixed-depth approach at the less than 0.01 cubic meters per cubic meter RF site (pit, 5.80 kilograms C per square meter; hammer, 4.74 kilograms C per square meter) and at the 0.14 cubic meters per cubic meter RF site (pit, 8.81 kilograms C per square meter; hammer, 6.71 kilograms C per square meter). The hammer corer also underestimated rho (sub b) at all sites as did the hydraulic push corer at the 0.21 cubic meters per cubic meter RF site. No significant differences in mass-based SOC stock estimates were observed between pits and corers. Our results indicate that (i) calculating SOC stocks on a mass basis can overcome biases in RF and rho (sub b) estimates introduced by sampling equipment and (ii) a quantitative pit is the optimal sampling method for establishing reference soil masses, followed by rotary and then hydraulic push corers.

hammer method↗

NASA NTRS1992

OSEE responses on D6AC steel due to sample preparation

A cleaning procedure and a contamination method developed at NASA Langley to contaminate sample surfaces with a certain thickness of HD-2 grease are demonstrated. Varying levels of contamination are obtained. Optically stimulated electron emission (OSEE) measurements were performed using the parallel electric field cell and the Pat scan device for clean and contaminated samples with a known amount of common contaminant. The OSEE response is found to be more sensitive for the clean sample than for the contaminated one. It is concluded that the OSEE measurements obtained using these techniques are sensitive to surface conditions and the contaminant thickness variations. It is also shown that the wavelength of illuminating light can have a profound effect on OSEE current levels.

Abedin, M. N.↗

NASA NTRS1972

The determination of iron, titanium, and nickel in Apollo 14 samples by cathode ray polarography.

Methods have been developed and applied to the determination of iron, titanium, and nickel in Apollo 14 fine soil and rock by differential cathode ray polarography on the same sample. A 5 mg sample was sufficient for the determination of all 3 elements. Iron and titanium were determined either directly or after cupferron separation. Nickel was determined after dimethylglyoxime separation.

Maienthal, E. J.↗

NASA NTRS1982

Accuracy of remotely sensed data: Sampling and analysis procedures

A review and update of the discrete multivariate analysis techniques used for accuracy assessment is given. A listing of the computer program written to implement these techniques is given. New work on evaluating accuracy assessment using Monte Carlo simulation with different sampling schemes is given. The results of matrices from the mapping effort of the San Juan National Forest is given. A method for estimating the sample size requirements for implementing the accuracy assessment procedures is given. A proposed method for determining the reliability of change detection between two maps of the same area produced at different times is given.

Congalton, R. G.↗

NASA NTRS1994

Clean assembly and integration techniques for the Hubble Space Telescope High Fidelity Mechanical Simulator

A mechanical simulator of the Hubble Space Telescope (HST) Aft Shroud was built to perform verification testing of the Servicing Mission Scientific Instruments (SI's) and to provide a facility for astronaut training. All assembly, integration, and test activities occurred under the guidance of a contamination control plan, and all work was reviewed by a contamination engineer prior to implementation. An integrated approach was followed in which materials selection, manufacturing, assembly, subsystem integration, and end product use were considered and controlled to ensure that the use of the High Fidelity Mechanical Simulator (HFMS) as a verification tool would not contaminate mission critical hardware. Surfaces were cleaned throughout manufacturing, assembly, and integration, and reverification was performed following major activities. Direct surface sampling was the preferred method of verification, but access and material constraints led to the use of indirect methods as well. Although surface geometries and coatings often made contamination verification difficult, final contamination sampling and monitoring demonstrated the ability to maintain a class M5.5 environment with surface levels less than 400B inside the HFMS.

Hughes, David W.↗

NASA NTRS1974

Study of sample of Sea of Fertility lunar surface material by the track method

Tracks in crystals of feldspars, olivines, pyroxenes, and in several fragments of basalts from a sample of Luna 16 lunar surface material were studied. A high track density, exceeding 10 to the 8th power cm/2 was found. The tracks were produced mainly by iron group nuclei of cosmic galactic and solar rays.

Poupeau, G.↗

NASA NTRS1985

Spline methods for approximating quantile functions and generating random samples

Two cubic spline formulations are presented for representing the quantile function (inverse cumulative distribution function) of a random sample of data. Both B-spline and rational spline approximations are compared with analytic representations of the quantile function. It is also shown how these representations can be used to generate random samples for use in simulation studies. Comparisons are made on samples generated from known distributions and a sample of experimental data. The spline representations are more accurate for multimodal and skewed samples and to require much less time to generate samples than the analytic representation.

Schiess, J. R.↗

NASA NTRS1992

Method of remotely characterizing thermal properties of a sample

A sample in a wind tunnel is radiated from a thermal energy source outside of the wind tunnel. A thermal imager system, also located outside of the wind tunnel, reads surface radiations from the sample as a function of time. The produced thermal images are characteristic of the heat transferred from the sample to the flow across the sample. In turn, the measured rates of heat loss of the sample are characteristic of the flow and the sample.

Heyman, Joseph S.↗

NASA NTRS1993

Use of Unlabeled Samples for Mitigating the Hughes Phenomenon

The use of unlabeled samples in improving the performance of classifiers is studied. When the number of training samples is fixed and small, additional feature measurements may reduce the performance of a statistical classifier. It is shown that by using unlabeled samples, estimates of the parameters can be improved and therefore this phenomenon may be mitigated. Various methods for using unlabeled samples are reviewed and experimental results are provided.

Landgrebe, David A.↗

NASA NTRS2022

Low Temperature Brazing: A Candidate Method for Preventing Interplanetary Contamination During the Mars Sample Return Mission

NASA and the European Space Agency are planning a joint Mars Sample Return campaign, scheduled to launch in 2026, with a very specific objective: return to Earth the rock and regolith samples that have been collected on Mars by NASA’s Perseverance rover. This is a very complex, multi-step process intended to culminate in the safe return of Mars samples to Earth. The term “safe return” implies use of a robust containment vessel designed to prevent any uncontained or unsterilized material from Mars from being returned to Earth. Hence, any technology chosen for sealing this vessel has to meet stringent contamination requirements, but also to withstand impact forces upon landing. This paper describes the development of a primary candidate for the sealing approach: brazing.

Schein, Mike↗

NASA NTRS2008

Using Optically Stimulated Electron Emission as an Inspection Method to Monitor Surface Contamination

During redesign of the Space Shuttle reusable solid rocket motor (RSRM), NASA amended the contract with ATK Launch Systems (then Morton Thiokol Inc.) with Change Order 966 to implement a contamination control and cleanliness verification method. The change order required: (1) A quantitative inspection method (2) A written record of actual contamination levels versus a known reject level (3) A method that is more sensitive than existing methods of visual and black light inspection. Black light inspection is only useful for inspection of contaminants that fluoresce near the 365 nm spectral line and is not useful for inspection of most silicones that will not produce strong fluorescence. Black light inspection conducted by a qualified inspector under controlled light is capable of detecting Conoco HD-2 grease in gross amounts and is very subjective due to operator sensitivity. Optically stimulated electron emission (OSEE), developed at the Materials and Process Laboratory at Marshall Space Flight Center (MSFC), was selected to satisfy Change Order 966. OSEE offers several important advantages over existing laboratory methods with similar sensitivity, e.g., spectroscopy and nonvolatile residue sampling, which provide turn around time, real time capability, and full coverage inspection capability. Laboratory methods require sample gathering and in-lab analysis, which sometimes takes several days to get results. This is not practical in a production environment. In addition, these methods do not offer full coverage inspection of the large components

Lingbloom, Mike S.↗

NASA NTRS1995

Spacelab Charcoal Analyses

This report describes analytical methods and results obtained from chemical analysis of 31 charcoal samples in five sets. Each set was obtained from a single scrubber used to filter ambient air on board a Spacelab mission. Analysis of the charcoal samples was conducted by thermal desorption followed by gas chromatography/mass spectrometry (GC/MS). All samples were analyzed using identical methods. The method used for these analyses was able to detect compounds independent of their polarity or volatility. In addition to the charcoal samples, analyses of three Environmental Control and Life Support System (ECLSS) water samples were conducted specifically for trimethylamine.

Slivon, L. E.↗

NASA NTRS2023

Statistical Approach on Utilizing Ground-Based Experiments to Model Break-Up Events

Two laboratory-based impact tests have been conducted to develop and extend the capability of NASA satellite breakup models. The first experiment, the Satellite Orbital Debris Characterization Impact Test (SOCIT), was conducted by the U.S. Department of Defense and NASA in 1992. It employed a fully functional U.S. Navy Transit spacecraft, fabricated from materials commonly used in the 1960s. SOCIT fragmentation data formed the basis of the current NASA Standard Satellite Breakup Model (SSBM). A second experiment, DebriSat, was conducted in 2014 by the DebriSat consortium: the NASA Orbital Debris Program Office, the United States Space Force Space Systems Command, formerly the Air Force Space and Missile Systems Center, the Air Force Arnold Engineering Development Complex, and the University of Florida. This impact test was performed on a high-fidelity mock-up satellite assembled from modern components. Data from both experiments are expected to contribute to the next-generation models for on-orbit breakup analyses, long-term environment predictions, and debris risk assessment. This paper uses the direct statistical sampling of the SOCIT and DebriSat data ensembles to model an on-orbit breakup event, rather than the analytic expressions estimated from the samples in the SSBM and its predecessor. This direct method involves drawing fragments (i.e., sampling with replacement) from each fragmentation data-subset containing mass, shape category, material density, characteristic length, mass, and cross-sectional area. As part of the sampling process, the properties of sampled fragment data (e.g., area-to-mass ratios) are numerically checked to ensure they do not contain unrealistic quantities. The process to simulate a breakup cloud composed of fragments from SOCIT and DebriSat datasets is discussed. The methodology for ensuring that conservation of overall mass of the sampled fragment cloud under this sampling approach is highlighted. Finally, the results are compared with simulated clouds generated from SSBM for specific historical breakup events.

Andrew Vavrin↗