Results for “thought experiments” — Page 10

NASA NTRS2017

The Dangers of Parametrics

Building a parametric cost model is hard work. The data is noisy and often does not behave like we want it to. We need statistics to give us an indication of the goodness of our models, but; statistics can be manipulated and mislead. On top of all of that, our own very human biases can lead us astray; causing us to see patterns in the noise and draw false conclusions from the data. Yet, it is the data itself that is the foundation for making better cost estimates and cost models. I believe the mistake we often make is we believe that our models are representative of the data; that our models summarize the experiences, the knowledge, and the stories contained in the data. However, it is the opposite that is true. Our models are but imitations of reality. They give us trends, but not truth. The experiences, the knowledge, and the stories that we need in order to make good cost estimates is bound up in the data. You cannot separate good cost estimating from a knowledge of the historical data. One final thought. It is our attempts to make sense out of the randomness that leads us astray. In order to make progress as cost modelers and cost estimators, we must accept that there are real limitations on our ability to model the past and predict the future. I do not believe we should throw up our hands and say this is the best we can do. Rather, to see real improvement we must first recognize these limitations, avoid the easy but misleading solutions, and seek to find ways to better model the world we live in. I don't have any simple solutions. Perhaps the answers lie in better data or in a totally different approach to simulating how the world works. All I know is that we must do our best to speak truth to ourselves and our customers. Misleading ourselves and our customers will, in the end, result in an inability to have a positive impact on those we serve.

Prince, Frank A.↗

NASA NTRS2017

The Dangers of Parametrics

Building a parametric cost model is hard work. The data is noisy and often does not behave like we want it to. We need statistics to give us an indication of the goodness of our models, but; statistics can be manipulated and mislead. On top of all of that, our own very human biases can lead us astray; causing us to see patterns in the noise and draw false conclusions from the data. Yet, it is the data itself that is the foundation for making better cost estimates and cost models. I believe the mistake we often make is we believe that our models are representative of the data; that our models summarize the experiences, the knowledge, and the stories contained in the data. However, it is the opposite that is true. Our models are but imitations of reality. They give us trends, but not truth. The experiences, the knowledge, and the stories that we need in order to make good cost estimates is bound up in the data. You cannot separate good cost estimating from a knowledge of the historical data. One final thought. It is our attempts to make sense out of the randomness that leads us astray. In order to make progress as cost modelers and cost estimators, we must accept that there are real limitations on our ability to model the past and predict the future. I do not believe we should throw up our hands and say this is the best we can do. Rather, to see real improvement we must first recognize these limitations, avoid the easy but misleading solutions, and seek to find ways to better model the world we live in. I don't have any simple solutions. Perhaps the answers lie in better data or in a totally different approach to simulating how the world works. All I know is that we must do our best to speak truth to ourselves and our customers. Misleading ourselves and our customers will, in the end, result in an inability to have a positive impact on those we serve.

Prince, Frank A.↗

NASA NTRS1974

Skylab M551 Metals Melting Experiment

The objectives of the M551 Metals Melting Experiment are to (a) study behavior of molten metal, (b) characterize metals melted and solidified in the low gravity space environment compared to one-gravity of earth, and (c) determine feasibility of joining metals in space. The experiment used the electron beam (EB) and chamber of the M512 apparatus to make a dwell puddle and a melt in a rotating disc of varying thickness. Hence, the EB performed cut-through, full and partial penetration melts, in addition to a re-solidified button. The three disc materials were aluminum 2219-T87, 304 stainless steel and pure tantalum to provide a wide range of density and melting conditions. Observations to date include (a) the proof that EB welding, cutting and melting can be done successfully in low gravity. Earlier, some welding authorities had postulated that without gravity the EB would force the molten puddle out of contact. However, the experiment proved that surface tension forces predominate. (b) From the view-point of cast-solidification, small, equiaxed grains in Skylab specimens compared to large, elongated grains in ground-based specimens were observed. The former are thought to be associated with constitutional supercooling and nucleation where the latter are associated with dendritic solidification. In further support of the more equiaxed grain growth in Skylab, symmetric sub-grain patterns were frequently observed where there was much less symmetry in ground-based specimens. Further work is being done to explain the differences in solidification.

E C Mckannan↗

NASA NTRS1988

An alternative to Guyan reduction of finite-element models

Structural modeling is a key part of structural system identification for large space structures. Finite-element structural models are commonly used in practice because of their general applicability and availability. The initial models generated by using a standard computer program such as NASTRAN, ANSYS, SUPERB, STARDYNE, STRUDL, etc., generally contain tens of thousands of degrees of freedom. The models must be reduced for purposes of identification. Not only does the magnitude of the identification effort grow exponentially as a function of the number of degrees of freedom, but numerical procedures may also break down because of accumulated round-off errors. Guyan reduction is usually applied after a static condensation. Misapplication of Guyan reduction can lead to serious modeling errors. It is quite unfortunate and disappointing, since the accuracy of the original detailed finite-element model one tries very hard to achieve is lost by the reduction. First, why and how Guyan reduction always causes loss of accuracy is examined. An alternative approach is then introduced. The alternative can be thought of as an improvement of Guyan reduction, the Rayleigh-Ritz method, and in particular the recent algorithm of Wilson, Yuan, and Dickens. Unlike Guyan reduction, the use of the alternative does not need any special insight, experience, or skill for partitioning the structural degrees of freedom. In addition to model condensation, this alternative approach can also be used for predicting analytically, quickly, and economically, what are those structural modes that are excitable by a force actuator at a given trial location. That is, in the excitation of the structural modes for identification, it can be used for guiding the placement of the force actuators.

Lin, Jiguan Gene↗

NASA NTRS1994

Chondrule formation in lightning discharges

Chondrules represent a significant mass fraction of primitive meteorites. These millimeter-sized glassy droplets appear to be the products of intensive transient heating events. Their size distribution, chemical and mineral composition, texture, isotope composition suggest that chondrules were produced as a result of short-duration melting followed by rapid cooling of solid precursor particles. Gas-dynamics heating, magnetic reconnection, and electrostatic discharges are thought to be the leading candidates to explain chondrule formation. In this paper we summarize our recent theoretical progress on the effects of 'lightning' in the early solar system and also report on preliminary results from our laboratory experiments. Differential settling of various sized dust particles toward the midplane of the nebula is suspected to build large-scale charge separations that episodically relax via the electric breakdown of the nebular gas. The electrostatic discharge os analogous to lightning in the Earth's atmosphere.

Horanyi, M.↗

NASA NTRS2002

STS-107 Crew Interviews: David Brown MS1

STS-107 Mission Specialist 1 David Brown is seen during this preflight interview where he gives a quick overview of the mission before answering questions about his inspiration to become an astronaut and his career. Brown outlines his role in the mission in general, and specifically during the conducting of on-board science experiments. Brown discusses the following instruments and experiments in detail: ARMS (Advanced Respiratory Monitoring System), MEIDEX (Mediterranean Israeli Dust Experiment), Combustion Module 2, and FREESTAR (Fast Reaction Enables Science Technology and Research). He also describes the new primary payload carrier, the SPACEHAB research double module which doubles the amount of space available for research. Brown shares his thoughts about the importance of international cooperation in mission planning and the need for scientific research in space.

Source record↗

NASA NTRS2005

Optical Sensing of Combustion Instabilities in Gas Turbines

In a continuing program of research and development, a system has been demonstrated that makes high-speed measurements of thermal infrared radiance from gas-turbine engine exhaust streams. When a gas-turbine engine is operated under conditions that minimize the emission of pollutants, there is a risk of crossing the boundary from stable to unstable combustion. Combustion instability can lead to engine damage and even catastrophic failure. Sensor systems of the type under development could provide valuable data during the development testing of gas-turbine engines or of engine components. A system of the type under development makes high-speed measurements of thermal infrared radiance from the engine exhaust stream. The sensors of this system can be mounted outside the engine, which eliminates the need for engine case penetrations typical with other engine dynamics monitors. This is an important advantage in that turbine-engine manufacturers consider such penetrations to be very undesirable. A prototype infrared sensor system has been built and demonstrated on a turbine engine. This system includes rugged and inexpensive near-infrared sensors and filters that select wavelengths of infrared radiation for high sensitivity. In experiments, low-frequency signatures were consistently observed in the detector outputs. Under some conditions, the signatures also included frequency components having one or two radiance cycles per engine revolution. Although it has yet to be verified, it is thought that the low-frequency signatures may be associated with bulk-mode combustion instabilities or flow instabilities in the compressor section of the engine, while the engine- revolution-related signatures may be indicative of mechanical problems in the engine. The system also demonstrated the ability to detect transient high-radiance events. These events indicate hot spots in the exhaust stream and were found to increase in frequency during engine acceleration.

Markham, James R.↗

NASA NTRS1992

Astronomical variation experiments with a Mars general circulation model

In time scales of a hundred thousand to a million years, the eccentricity of Mars orbit varies in a quasi-periodic manner between extremes as large as 0.14 and as small as 0 and the tilt of its axis of rotation with respect to the orbit normal also varies quasi-periodically between extremes as large as 35 deg and as small as 15 deg. In addition, the orientation of the axis precesses on comparable time scales. These astronomical variations are much more extreme than those experienced by the Earth. These variations are thought to have strongly modulated the seasonal cycles of dust, carbon dioxide, and water. One manifestation of the induced quasiperiodic climate changes may be the layered terrain of the polar regions, with individual layers perhaps recording variations in the absolute and/or relative deposition rates of dust and water in the polar regions, most likely in association with the winter time deposition of carbon dioxide ice. In an attempt to understand the manner in which atmospheric temperatures and winds respond to the astronomical forcings, we have initiated a series of numerical experiments with the NASA/Ames general circulation model of the Martian Atmosphere.

Pollack, J. B.↗

NASA NTRS1984

Abrasion by aeolian particles: Earth and Mars

Estimation of the rate of aeolian abrasion of rocks on Mars requires knowledge of: (1) particle flux, (2) susceptibilities to abrasion of various rocks, and (3) wind frequencies on Mars. Fluxes and susceptibilities for a wide range of conditions were obtained in the laboratory and combined with wind data from the Viking meteorology experiment. Assuming an abundant supply of sand-sized particles, estimated rates range up to 2.1 x 10 to the minus 2 power cm of abrasion per year in the vicinity of Viking Lander 1. This rate is orders of magnitude too great to be in agreement with the inferred age of the surface based on models of impact crater flux. The discrepancy in the estimated rate of abrasion and the presumed old age of the surface cannot be explained easily by changes in climate or exhumation of ancient surfaces. The primary reason is thought to be related to the agents of abrasion. At least some sand-sized (approx. 100 micrometers) grains appear to be present, as inferred from both lander and orbiter observations. High rates of abrasion occur for all experimental cases involving sands of quartz, basalt, or ash. However, previous studies have shown that sand is quickly comminuted to silt- and clay-sized grains in the martian aeolian regime. Experiments also show that these fine grains are electrostatically charged and bond together as sand-sized aggregates. Laboratory simulations of wind abrasion involving aggregates show that at impact velocities capable of destroying sand, aggregates from a protective veneer on the target surface and can give rise to extremely low abrasion rates.

Greeley, R.↗

NASA NTRS1982

The spectrum of Titan in the far-infrared and microwave regions

The pressure-induced absorptions of gaseous nitrogen (N2) and methane (CH4) are computed on the basis of the collisional lineshape theory of Birnbaum and Cohen (1976). Laboratory data at 300 and 124 K for N2 and at 296 and 195 K for CH4 are used to determine the collisional time constants and their temperature dependence. The spectrum of Titan from the microwave to the far-infrared region (0.1-600/cm) is then modeled using these opacities and a temperature profile of Titan's atmosphere derived from the Voyager 1 radio occultation experiment. The model atmosphere is composed of N2 and CH4, their relative proportions being determined by the vapor pressure law of CH4. A model with gaseous opacity alone is ruled out by the far-infrared observations. An additional opacity, thought to be associated with a methane cloud, is confirmed. The effective temperature of Titan is estimated at 83.2 plus or minus 1.4 K.

Courtin, R.↗

NASA NTRS2014

Organic Analysis of Catalytic Fischer-Tropsch Synthesis Products and Ordinary Chondrite Meteorites by Stepwise Pyrolysis-GCMS: Organics in the Early Solar Nebula

Abiotic generation of complex organic compounds, in the early solar nebula that formed our solar system, is hypothesized by some to occur via Fischer-Tropsch (FT) synthesis. In its simplest form, FT synthesis involves the low temperature (<300degC) catalytic reaction of hydrogen and carbon monoxide gases to form more complex hydrocarbon compounds, primarily n-alkanes, via reactive nano-particulate iron, nickel, or cobalt, for example. Industrially, this type of synthesis has been utilized in the gas-to-liquid process to convert syngas, produced from coal, natural gas, or biomass, into paraffin waxes that can be cracked to produce liquid diesel fuels. In general, the effect of increasing reaction temperature (>300degC) produces FT products that include lesser amounts of n-alkanes and greater alkene, alcohol, and polycyclic aromatic hydrocarbon (PAH) compounds. We have begun to experimentally investigate FT synthesis in the context of abiotic generation of organic compounds in the early solar nebula. It is generally thought that the early solar nebula included abundant hydrogen and carbon monoxide gases and nano-particulate matter such as iron and metal silicates that could have catalyzed the FT reaction. The effect of FT reaction temperature, catalyst type, and experiment duration on the resulting products is being investigated. These solid organic products are analyzed by thermal-stepwise pyrolysis-GCMS and yield the types and distribution of hydrocarbon compounds released as a function of temperature. We show how the FT products vary by reaction temperature, catalyst type, and experimental duration and compare these products to organic compounds found to be indigenous to ordinary chondrite meteorites. We hypothesize that the origin of organics in some chondritic meteorites, that represent an aggregation of materials from the early solar system, may at least in part be from FT synthesis that occurred in the early solar nebula.

Locke, Darren R.↗

NASA NTRS1979

The role of phosphorus in the upper atmosphere of Jupiter

The reaction of elemental phosphorus and H atoms to form PH3 was observed and should be a major factor in the recycling of PH3 in the stratosphere of Jupiter. The formation of PH3 in this manner should predominate at high altitudes where, due to the very low temperatures, reactions that require higher activation energies than these atom reactions cannot occur. At lower altitudes, in the troposphere, the rapid formation of H atoms from the strong absorption of light by NH3 will contribute to phosphine production also in this same manner. Recent experiments have also shown that elemental phosphorus reacts readily with aqueous ammonia to form PH3. This reaction may also be important in the recycling of PH3 in the upper troposphere of Jupiter if water-ammonia clouds, as had been previously thought, exist. Considerations of the coloration of the Great Red Spot have been made based upon the nature of the phosphorus obtained by decomposition of the phosphine.

Howland, G. R.↗

NASA NTRS2014

Icing Analysis of a Swept NACA 0012 Wing Using LEWICE3D Version 3.48

Icing calculations were performed for a NACA 0012 swept wing tip using LEWICE3D Version 3.48 coupled with the ANSYS CFX flow solver. The calculated ice shapes were compared to experimental data generated in the NASA Glenn Icing Research Tunnel (IRT). The IRT tests were designed to test the performance of the LEWICE3D ice void density model which was developed to improve the prediction of swept wing ice shapes. Icing tests were performed for a range of temperatures at two different droplet inertia parameters and two different sweep angles. The predicted mass agreed well with the experiment with an average difference of 12%. The LEWICE3D ice void density model under-predicted void density by an average of 30% for the large inertia parameter cases and by 63% for the small inertia parameter cases. This under-prediction in void density resulted in an over-prediction of ice area by an average of 115%. The LEWICE3D ice void density model produced a larger average area difference with experiment than the standard LEWICE density model, which doesn't account for the voids in the swept wing ice shape, (115% and 75% respectively) but it produced ice shapes which were deemed more appropriate because they were conservative (larger than experiment). Major contributors to the overly conservative ice shape predictions were deficiencies in the leading edge heat transfer and the sensitivity of the void ice density model to the particle inertia parameter. The scallop features present on the ice shapes were thought to generate interstitial flow and horse shoe vortices which enhance the leading edge heat transfer. A set of changes to improve the leading edge heat transfer and the void density model were tested. The changes improved the ice shape predictions considerably. More work needs to be done to evaluate the performance of these modifications for a wider range of geometries and icing conditions

Ice Accretion Software↗

NASA NTRS2014

Icing Analysis of a Swept NACA 0012 Wing Using LEWICE3D Version 3.48

Icing calculations were performed for a NACA 0012 swept wing tip using LEWICE3D Version 3.48 coupled with the ANSYS CFX flow solver. The calculated ice shapes were compared to experimental data generated in the NASA Glenn Icing Research Tunnel (IRT). The IRT tests were designed to test the performance of the LEWICE3D ice void density model which was developed to improve the prediction of swept wing ice shapes. Icing tests were performed for a range of temperatures at two different droplet inertia parameters and two different sweep angles. The predicted mass agreed well with the experiment with an average difference of 12%. The LEWICE3D ice void density model under-predicted void density by an average of 30% for the large inertia parameter cases and by 63% for the small inertia parameter cases. This under-prediction in void density resulted in an over-prediction of ice area by an average of 115%. The LEWICE3D ice void density model produced a larger average area difference with experiment than the standard LEWICE density model, which doesn't account for the voids in the swept wing ice shape, (115% and 75% respectively) but it produced ice shapes which were deemed more appropriate because they were conservative (larger than experiment). Major contributors to the overly conservative ice shape predictions were deficiencies in the leading edge heat transfer and the sensitivity of the void ice density model to the particle inertia parameter. The scallop features present on the ice shapes were thought to generate interstitial flow and horse shoe vortices which enhance the leading edge heat transfer. A set of changes to improve the leading edge heat transfer and the void density model were tested. The changes improved the ice shape predictions considerably. More work needs to be done to evaluate the performance of these modifications for a wider range of geometries and icing conditions.

Icing CFD↗

NASA NTRS2022

Characterizing Student-Driven Research Investigations Contributed to the GLOBE Program Citizen Science Initiative in a Formal Education Context

The Global Learning and Observations to Benefit the Environment (GLOBE) Program offers citizen science opportunities to participants of all ages, with a focus on youth in formal classroom contexts. This study uses student investigation research reports and posters submitted to the 2018 International Virtual Science Symposium (IVSS) and Student Research Symposium (SRS) as testbeds for characterizing student-driven Earth system citizen science investigations. Secondarily, this study aimed to capture GLOBE’s alignment to existing citizen science outcomes frameworks in the literature, which have primarily focused on adults and non-formal settings. Based on a literature review, the evaluation team identified 89 potential characteristics in 27 categories to typify investigations from both formal education and citizen science perspectives. We coded the artifacts from 207 student projects, conducted quantitative analysis of frequencies, and performed a semantic network analysis. By using this networking approach, we conceptually mapped several clusters of co-occurring characteristics, defining a descriptive framework for GLOBE projects. We identified three tiers of citizen science projects, increasing in the sophistication of participants’ demonstrated science practices. The framework includes additional components that reflect student citizen scientists’ thoughtfulness and connection to context as well as their projects’ reflection of their motivation and self efficacy. Through these findings, we have identified areas where student citizen scientists would benefit from further support, and suggest here further research to incorporate the experiences of students into the broader understanding of citizen science outcomes.

network analysis↗

NASA NTRS1976

Autoignition - A liquid propellant explosive potential limiting phenomena

It has been thought that the unplanned mixing of the propellants of liquid launch vehicles could result in massive explosion and destruction. This paper presents results of NASA's attempt to develop a precise analytical theory and predictive model for liquid propellant explosives. Prediction model experiments involving a 'seven-chart' approach showing the relationship between yield function, mixing function, time dependence, chemical and physical reactant properties and quantity effects were used to establish a theory that autoignition takes place when propellants mix in a certain 'critical mass' or greater. An analytical confirmation of the theory has been carried out, with particular reference to possible autoignition in LOX/LH2 and LOX/RP-1 and Saturn V: it was confirmed that autoignition occurs and prevents the mixing of more than the 'critical mass' and therefore limits the explosive yield to several thousand pounds, which will disperse the remaining propellant and prohibit detonation of the total quantities otherwise suspected.

Boggs, W. H.↗

NASA NTRS1978

Future timing accuracy requirements and procedures for data processing

Timing accuracy requirements for satellite experiment data are discussed. Although time accuracies of 100 milliseconds were sufficient when OSO-3, 4, 5 were launched in the mid-60s, time accuracies of 100 microseconds are necessary for OSO-8, HEAO-A, and Seasat, and it is thought likely that accuracies of 10 microseconds will become routine in the 1980s. An approach to the problem of identifying the sources of spacecraft timing errors - from the onboard counters to the final tagging of data - is considered.

Smith, G. A.↗

NASA NTRS1986

The Expert Project Management System (EPMS)

Successful project managers (PMs) have been shown to rely on 'intuition,' experience, and analogical reasoning heuristics. For new PMs to be trained and experienced PMs to avoid repeating others' mistakes, it is necessary to make the knowledge and heuristics of successful PMs more widely available. The preparers have evolved a model of PM thought processes over the last decade that is now ready to be implemented as a generic PM aid. This aid consists of a series of 'specialist' expert systems (CRITIC, LIBRARIAN, IDEA MAN, CRAFTSMAN, and WRITER) that communicate with each other via a 'blackboard' architecture. The various specialist expert systems are driven to support PM training and problem solving since any 'answers' they pass to the blackboard are subjected to conflict identification (AGENDA FORMULATOR) and GOAL SETTER inference engines.

Silverman, Barry G.↗