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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 235 records · Page 13

NASA Human Spaceflight Scenarios - Do All Our Models Still Say No?

Historically, NASA human spaceflight planning has included healthy doses of life cycle cost analysis. Planners put projects and their cost estimates in a budget context. Estimated costs became expected budgets. Regardless, real budgets rarely matched expectations. So plans would come and go as NASA canceled projects. New projects would arise and the cycle would begin again. Repeatedly, NASA schedule and performance ambitions come up against costs growing at double-digit rates while budgets barely rise a couple of percent a year. Significant skepticism greets proposed NASA programs at birth, as cost estimates for new projects are traditionally very high, and worse, far off the mark for those carried forward. In this environment the current "capability driven framework" for NASA human spaceflight evolved, where long term life cycle cost analysis are even viewed as possibly counter-productive. Here, a space exploration project, for example the Space Launch System, focuses on immediate goals. A life cycle is that of a project, not a program, and for only that span of time to a near term milestone like a first test launch. Unfortunately, attempting to avoid some pitfalls in long-term life cycle cost analysis breeds others. Government audits have noted that limiting the scope of cost analysis "does not provide the transparency necessary to assess long-term affordability" making it difficult to understand if NASA "is progressing in a cost-effective and affordable manner." Even in this short-term framework, NASA realizes the importance of long-term considerations, that it must "maximize the efficiency and sustainability of the Exploration Systems development programs", that this is "critical to free resources for re-investment...such as other required deep space exploration capabilities." Assuming the value of long-term life cycle cost analysis, where due diligence meets reconnaissance, and accepting past shortcomings, the work here approaches life cycle cost analysis for human spaceflight differently. 1) If costs have traditionally been so high that adding them up is discouraging, are there any new facts on the ground offering paths to significantly lower costs? 2) If NASA's spaceflight budget and process is an over-arching constraint, with its planning limitations favoring short-term outlooks, is there a way to step outside the budget box? 3) If life cycle answers have historically been too uncertain to be useful, is there a process where stakeholders gain valuable insights merely from emphasizing a common understanding around questions? We analyze the potential life cycle cost of assorted NASA human spaceflight architectures - an architecture as a sum of individual systems, working together. With the prior questions of high costs, limited budgets and uncertainties in mind, public private partnerships are central in these architectures. The cost data for current commercial public private partnerships is encouraging, as are cost estimates for future partnership approaches beyond low Earth orbit. Private capital, directly or indirectly, an ingredient of public private partnerships, may be a significant factor in finding a path around the limits of the NASA spaceflight budget. Also, understanding and reviewing the pros, cons and uncertainties of assorted architectures can assist in developing a common understanding around key questions as important if not more so than the numbers and answers. Lastly, a scenario planning technique is briefly explored that can mature a common understanding about the agencies situation at hand and how diverse stakeholders can go forward together. Scenario planning, rather than focusing on answers, places emphasis on stakeholders developing a common understanding about the future. Putting aside costs, this is especially true of questions about sustainability and growth, results, benefits and expectations. While efficiency exercises or analysis look to reduce resources in one place to apply them elsewhere, moving around slices in a pie, scenario planning can get at the heart of the matter, growing the pie, transforming it, and making the pieces relevant. Especially important is the question of sustainability for different scenarios in the broad sense of the word - not just the narrow ability to survive or continue, but also the ability to adapt, prosper and grow.

space systems life cycle costs↗

Observing System Simulation Experiments

Observing System Simulation Experiments can be powerful tools for evaluating and exploring both the behavior of data assimilation systems and the potential impacts of future observing systems. With great power comes great responsibility - given a pure modeling framework, how can we be sure our results are meaningful? The challenges and pitfalls of OSSE calibration and validation will be addressed, as well as issues of incestuousness, selection of appropriate metrics, and experiment design. The use of idealized observational networks to investigate theoretical ideas in a fully complex modeling framework will also be discussed.

Prive, Nikki↗

Spacecraft Micro-Vibration: A Survey of Problems, Experiences, Potential Solutions, and Some Lessons Learned

Predicting, managing, controlling, and testing spacecraft microvibrations due to on-board internal disturbance sources is a formidable multi-disciplinary systems engineering challenge, especially for those observatories hosting extremely sensitive optical sensor payloads with stringent requirements on allowable line-of-sight jitter. In this paper some specific spacecraft micro-vibration engineering challenges will be introduced and described. Technical background context is provided with the inclusion of several illustrative examples of NASA and European Space Agency missions (both past and present) where dynamic interactions have to be addressed and which have demanding payload instrument line-of-sight jitter requirements. A general modeling, analysis, simulation, and test approach to address and solve the overall problem of spacecraft micro-vibrations is outlined. Recommended rules of thumb are presented to provide guidance for analysts on where to initiate and how to approach a new spacecraft micro-vibration design problem. A set of experience-based spacecraft micro-vibration lessons learned are also presented in the hope they can be leveraged on new system development projects to help overcome unfamiliarity with previously identified microvibration technical pitfalls and challenges.

Dennehy, Cornelius↗

Modern Modal Testing: A Cautionary Tale

Over the past 50 years, great advances have been achieved in both analytical modal analysis (i.e. finite element models and analysis) and experimental modal analysis (i.e. modal testing) in aerospace and other fields. With the advent of more powerful computers, higher performance instrumentation and data acquisition systems, and powerful linear modal extraction tools, analysts and test engineers have a breadth and depth of technical resources only dreamed of by our predecessors. However, some observed recent trends indicate that hard lessons learned are being forgotten or ignored, and possibly fundamental concepts are not being understood. These trends have the potential of leading to the degradation of the quality of and confidence in both analytical and test results. These trends are a making of our own doing, and directly related to having ever more powerful computers, programmatic budgetary pressures to limit analysis and testing, and technical capital loss due to the retirement of the senior component of a bimodal workforce. This paper endeavors to highlight some of the most important lessons learned, common pitfalls to hopefully avoid, and potential steps that may be taken to help reverse this trend.

bimodal workforce↗

European Service Module - Structural Test Article (E-STA) Building Block Test Approach and Model Correlation Observations

The Orion European Service Module - Structural Test Article (E-STA) underwent sine vibration testing in 2016 using the Mechanical Vibration Facility (MVF) multi-axis shaker system at NASA Glenn Research Center’s (GRC) Plum Brook Station (PBS) Space Power Facility (SPF). The main objective was to verify the structural integrity of the European Service Module (ESM) under sine sweep dynamic qualification vibration testing. A secondary objective was to perform a fixed-base modal survey, while E-STA was still mounted to MVF, in order to achieve a test correlate the finite element model (FEM). To facilitate the E-STA system level correlation effort, a building block test approach was implemented. Modal tests were performed on two major subassemblies, the crew module/launch abort structure (CM/LAS) and the crew module adapter (CMA) mass simulators. These subassembly FEMs were individually correlated and then integrated into the E-STA FEM prior to the start of the E-STA sine vibration test. This paper summarizes the modal testing and model correlation efforts of both of these subassemblies and how the building block approach assisted in the overall correlation of the E-STA FEM. This paper will also cover modeling practices that should be avoided, recommended instrumentation positioning on complex structures, and the importance of the FEM geometrically matching CAD in sufficient detail in order to adequately replicate internal load paths. The goal of this paper is to inform the reader of the hard earned lessons learned and pitfalls to avoid when applying a building block test approach.

Winkel, James P.↗

Modern Modal Testing: A Cautionary Tale IMAC XXVII

Over the past 50 years, great advances have been achieved in both analytical modal analysis (i.e. finite element models and analysis) and experimental modal analysis (i.e. modal testing) in aerospace and other fields. With the advent of more powerful computers, higher performance instrumentation and data acquisition systems, and powerful linear modal extraction tools, analysts and test engineers have a breadth and depth of technical resources only dreamed of by our predecessors. However, some observed recent trends indicate that hard lessons learned are being forgotten or ignored, and possibly fundamental concepts are not being understood. These trends have the potential of leading to the degradation of the quality of and confidence in both analytical and test results. These trends are a making of our own doing, and directly related to having ever more powerful computers, programmatic budgetary pressures to limit analysis and testing, and technical capital loss due to the retirement of the senior component of a bimodal workforce. This paper endeavors to highlight some of the most important lessons learned, common pitfalls to hopefully avoid, and potential steps that may be taken to help reverse this trend.

bimodal workforce↗

Analyzing Machine Learning Predictions of Passive Microwave Brightness Temperature Spectral Difference Over Snow-Covered Terrain in High Mountain Asia

Snow is an important component of the terrestrial freshwater budget in high mountainAsia (HMA) and contributes to the runoff in Himalayan rivers through snowmelt. Despitethe importance of snow in HMA, considerable spatiotemporal uncertainty exists across the different estimates of snow water equivalent for this region. In order to better estimate snow water equivalent, radiative transfer models are often used in conjunction with microwave brightness temperature measurements. In this study, the efficacy of support vector machines (SVMs), a machine learning technique, to predict passive microwave brightness temperature spectral difference (1Tb) as a function of geophysical variables (snow water equivalent, snow depth, snow temperature, and snow density) is explored through a sensitivity analysis. The use of machine learning (as opposed to radiative transfer models) is a relatively new and novel approach for improving snow water equivalent estimates. The Noah-MP land surface model within the NASALand Information System framework is used to simulate the hydrologic cycle over HMA and model geophysical variables that are then used for SVM training. The SVMsserve as a nonlinear map between the geophysical space (modeled in Noah-MP) andthe observation space (1Tb as measured by the radiometer). Advanced MicrowaveScanning Radiometer-Earth Observing System measured passive microwave brightness temperatures over snow-covered locations in the HMA region are used as training data during the SVM training phase. Sensitivity of well-trained SVMs to each Noah-MP modeled state variable is assessed by computing normalized sensitivity coefficients. Sensitivity analysis results generally conform with the known first-order physics. Input states that increase volume scattering of microwave radiation, such as snow density and snow water equivalent, exhibit a plurality of positive normalized sensitivity coefficients. In general, snow temperature was the most sensitive input to the SVM predictions. The sensitivity of each state is location and time dependent. The signs of normalized sensitivity coefficients that indicate physical irrationality are ascribed to significant cross-correlation between Noah-MP simulated states and decreased SVM prediction capability at specific locations due to insufficient training data. SVM prediction pitfalls do exist that serve to highlight the limitations of this particular machine learning algorithm.

high mountain Asia↗

Overcoming the Challenges of Data Integration and Automation

Artificial Intelligence (AI) and machine learning (ML) are gaining increased attention as a way to leverage the world's data to solve problems. Although AI and ML offer much potential, there are often misconceptions about the application of such techniques. This panel discussion includes speakers from airlines and the research community who will present machine learning approaches they have developed on a variety of aviation data including digital flight data, safety reporting data, and traffic flow data. They will explain the purpose of the application, the data used, and the lessons learned in the development and deployment of their solutions. The panel discussion will focus on common pitfalls in developing and AI solution, the dangers of the current hype around AI, tips for gaining value from a machine learning solution, how to determine whether a machine learning approach is appropriate for a problem, and more.

Matthews, Bryan L.↗

Artificial Intelligence in Aviation Safety Applications - Exploring Myths and Truths of AI and ML

Artificial Intelligence (AI) and machine learning (ML) are gaining increased attention as ways to leverage the world's data to solve problems. Although AI and ML offer much potential, there are often misconceptions about the application of such techniques.Panel speakers will present machine learning approaches they have developed on a variety of aviation data, including digital flight data, safety reporting data, and voice communications data. They will discuss the purpose of the application, the data used, and the lessons learned in the development and deployment of their solutions. The panel will also discuss common pitfalls in developing an AI solution, the dangers of the current hype around AI, tips for gaining value from a ML solution, how to determine whether a ML approach is appropriate for a problem, and more.

Reeves, Scott (Capt.)↗

A Survey of the Spacecraft Line-Of-Sight Jitter Problem

Predicting, managing, controlling, and testing spacecraft Line-of-Sight (LoS) jit- ter due to on-board internal disturbance sources is a challenging multi- disciplinary systems engineering problem, especially for those observatories hosting extremely sensitive optical sensor payloads with stringent requirements on allowable LoS jitter. Some specific spacecraft jitter engineering challenges will be introduced and described in this survey paper. Illustrative examples of missions where dynamic interactions have to be addressed to satisfy demanding payload instrument LoS jitter requirements will be provided. Some lessons learned and a set of recommended rules of thumb are also presented to provide guidance for analysts on where to initiate and how to approach a new spacecraft jitter design problem. These experience-based spacecraft jitter lessons learned and rules of thumb are provided in the hope they can be leveraged on new space system development projects to help overcome unfamiliarity with previously identified jitter technical pitfalls and challenges.

Dennehy, Cornelius J.↗

Lessons Learned from Recent Space Flight Assessments

This paper highlights four space flight assessments, each with an important lesson. The first assessment points to the challenge of material substitution for weight saving. Space Shuttle’s external tank stringers were changed from Al 2024 to Al 2090 without comprehensive analysis. Lack of understanding the low Short-Transverse (S-T) strength associated with Al 2090 led to widespread cracking. The second assessment addresses the failure to understand that time-dependent relationships and loading interactions of multiple disciplines can lead to non-conservative results. An aerodynamic test article of the Orion Multi-Purpose Crew Vehicle (MPCV) Launch Abort System (LAS) was analyzed for worst-case single discipline loads, showing positive structural margins. When disciplines were combined with time dependent loading, the analysis resulted in negative margins. The third assessment highlights the pitfalls of putting blind trust in historical architecture. The MPCV re-entry heat shield adopted the Apollo design approach despite fundamental differences between the two designs (e.g., the underlying substructure design, material differences, scale, and geometry). Manufacturing resulted in cracking along seams of the cured MPCV heat shield and produced lower mechanical properties of the Avcoat witness panels. Subsequently, the design was changed to a block architecture, which introduced unperceived technical, cost, and schedule risk. The fourth assessment shows how the lack of a comprehensive investigation of design modifications and inappropriate Finite Element Analyses (FEA) can lead to trouble. A mass reduction campaign eliminated highly critical internal struts on the ISS Node-1 pressurized module based on inadequate and uncorrelated FEA. High strains were noted and ignored as a modeling aberration. A system level high fidelity FEA discovered large plastic strains in the gussets of all four radial ports. These findings initiated a full-scale test campaign, new test correlated assembly-level FEA, and significant design modifications.

James P Smith↗

Cryogenic Technologies for the Stratospheric Observatory for Infrared Astronomy (SOFIA) Science Instruments

This work was performed at the request of the Program Chief Engineer for Stratospheric Observatory for Infrared Astronomy (SOFIA). The intended audience for this position paper is the prospective SOFIA Science Instrument (SI) developer, who may not have extensive experience with cryogenics or cryostat design. The objective is to provide an introductory handbook that (1) concisely summarizes SOFIA requirements, (2) describes components and techniques that enable cryostats to reach temperatures ranging from 4 K to 50 mK, and (3) warns of common pitfalls that an SI developer might encounter.

Stratospheric Observatory for Infrared Astronomy↗

A Computational Analysis of Boundary Layer Instability over the BOLT Configuration

The complex boundary layer flow over the BOLT flight configuration is known to exhibit multiple and potentially interacting instability mechanisms. This paper represents a continuation of our numerical investigation of the flow instabilities over the main test surface of the BOLT configuration by using state-of-the-art tools in multidimensional instability analysis. Specifically, the paper extends our previous computations by considering the separate effects of a nonzero angle of attack and a nonzero yaw on the modal instability characteristics of the boundary layer streaks adjacent to the minor-axis symmetry plane, specifically near both ends of the azimuthal region of a thick boundary layer in the middle, where this region rapidly changes to a thinner boundary layer on either side. At the t = 28.8767 s condition from the ascent part of the anticipated flight trajectory with a flight Mach number of M ∞ = 5.53 and unit Reynolds number of 4.25 x 10 6 /m, either type of departure from the design condition is shown to have a considerable impact on the structure of the basic state rollup within the region of interest and, hence, also on the amplification characteristics of instability waves within the resulting streaks. Yet, for a yaw angle of β = 4 degrees, the computations indicate only a slight reduction with respect to the peak N-factor of nearly 11 at the design condition of zero degrees yaw and zero degrees angle of attack. In contrast, an angle of attack equal to α = 4 degrees, the peak N-factor decreases to nearly 6 on the leeward side and increases above 16 on the windward side, making the onset of transition highly likely on the windward side. Computations also highlight the role of streak instabilities that originate as Mack mode disturbances and also demonstrate the potential pitfalls in using surface pressure sensors alone to gauge the magnitude of instability amplification.

Boundary layer transition↗

Lessons Learned from Large-Scale Aerospace Structural Testing

Large-scale testing of aerospace structures is frequently the final step in a development project to validate the structural performance, and that typically involves a large cost and time investment. In order to ensure that the testing provides the required data, avoiding errors that can result in an unsuccessful test and failure to meet objectives is critical. Presented herein are five lessons learned to provide insight to those conducting tests in order to help them avoid known pitfalls that may result in an unsuccessful test. Five subject large-scale tests are described, and include two composite wing tests, a composite hybrid-wing body center section test, a full-scale 27.5-ft diameter metallic barrel test, and an 8-ft diameter metallic barrel test. Problems identified during the testing and mitigation approaches to solve the problems are presented, then the lessons learned are summarized.

Lessons Learned↗

Lessons Learned from Large-Scale Aerospace Structural Testing

Large-scale testing of aerospace structures is frequently the final step in a development project to validate the structural performance, and that typically involves a large cost and time investment. In order to ensure that the testing provides the required data, avoiding errors that can result in an unsuccessful test and failure to meet objectives is critical. Presented herein are five lessons learned to provide insight to those conducting tests in order to help them avoid known pitfalls that may result in an unsuccessful test. Five subject large-scale tests are described, and include two composite wing tests, a composite hybrid-wing body center section test, a full-scale 27.5-ft diameter metallic barrel test, and an 8-ft diameter metallic barrel test. Problems identified during the testing and mitigation approaches to solve the problems are presented, then the lessons learned are summarized.

Lessons Learned↗

A Computational Analysis of Boundary Layer Instability over the BOLT Configuration (Effect of Nonzero AoA and Yaw)

The complex boundary layer flow over the BOLT flight configuration is known to exhibit multiple and potentially interacting instability mechanisms. This paper represents a continuation of our numerical investigation of the flow instabilities over the main test surface of the BOLT configuration by using state-of-the-art tools in multidimensional instability analysis. Specifically, the paper extends our previous computations by considering the separate effects of a nonzero angle of attack and a nonzero yaw on the modal instability characteristics of the boundary layer streaks adjacent to the minor-axis symmetry plane, specifically near both ends of the azimuthal region of a thick boundary layer in the middle, where this region rapidly changes to a thinner boundary layer on either side. At the t = 28.8767 s condition from the ascent part of the anticipated flight trajectory with a flight Mach number of M ∞ = 5.53 and unit Reynolds number of 4.25 x 10 6 /m, either type of departure from the design condition is shown to have a considerable impact on the structure of the basic state rollup within the region of interest and, hence, also on the amplification characteristics of instability waves within the resulting streaks. Yet, for a yaw angle of β = 4 degrees, the computations indicate only a slight reduction with respect to the peak N-factor of nearly 11 at the design condition of zero degrees yaw and zero degrees angle of attack. In contrast, an angle of attack equal to α = 4 degrees, the peak N-factor decreases to nearly 6 on the leeward side and increases above 16 on the windward side, making the onset of transition highly likely on the windward side. Computations also highlight the role of streak instabilities that originate as Mack mode disturbances and also demonstrate the potential pitfalls in using surface pressure sensors alone to gauge the magnitude of instability amplification.

Boundary layer transition↗

TOPEX Microwave Radiometer Thermal Control: Post-System-Test Modifications and On-Orbit Performance

The Topex Microwave Radiometer has had an excellent thermal performance since launch. The instrument, however, went through a hardware modification right before launch to correct for athermal design inadequacy that was uncovered during the spacecraft thermal vacuum test. This paper reports on how the initially obscure problem was tracked down, and how the thermal models were revised, validated, and utilized to investigate the solution options and guide the hardware modification decisions. Details related to test data interpretation, analytical uncertainties, and model-prediction vs. test-data correlation, are documented. Instrument/spacecraft interface issues, where the problem originated and where in general pitfalls abound, are dealt with specifically. Finally, on-orbit thermal performance data are presented, which exhibit good agreement with flight predictions, and lessons learned are discussed.

Lin, Edward I.↗