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Results for “reasoning”

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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Evidence of pathogenic microbes in the International Space Station drinking water: reason for concern?

Molecular analyses were carried out on four preflight and six postflight International Space Station (ISS)-associated potable water samples at various stages of purification, storage, and transport, to ascertain their associated microbial diversities and overall microbial burdens. Following DNA extraction, PCR amplification, and molecular cloning procedures, rDNA sequences closely related to pathogenic species of Acidovorax, Afipia, Brevundimonas, Propionibacterium, Serratia, and others were recovered in varying abundance. Retrieval of sequences arising from the iodine (biocide)-reducing Delftia acidovorans in postflight waters is also of concern. Total microbial burdens of ISS potable waters were derived from data generated by an ATP-based enumeration procedure, with results ranging from 0 to 4.9 x 10(4) cells/ml. Regardless of innate biases in sample collection and analysis, such circumstantial evidence for the presence of viable, intact pathogenic cells should not be taken lightly. Implementation of new cultivation approaches and/or viability-based assays are requisite to confirm such an occurrence.

STS-113 Shuttle Project↗
NASA NTRS2005

Constraint-based Temporal Reasoning with Preferences

Often we need to work in scenarios where events happen over time and preferences are associated to event distances and durations. Soft temporal constraints allow one to describe in a natural way problems arising in such scenarios. In general, solving soft temporal problems require exponential time in the worst case, but there are interesting subclasses of problems which are polynomially solvable. In this paper we identify one of such subclasses giving tractability results. Moreover, we describe two solvers for this class of soft temporal problems, and we show some experimental results. The random generator used to build the problems on which tests are performed is also described. We also compare the two solvers highlighting the tradeoff between performance and robustness. Sometimes, however, temporal local preferences are difficult to set, and it may be easier instead to associate preferences to some complete solutions of the problem. To model everything in a uniform way via local preferences only, and also to take advantage of the existing constraint solvers which exploit only local preferences, we show that machine learning techniques can be useful in this respect. In particular, we present a learning module based on a gradient descent technique which induces local temporal preferences from global ones. We also show the behavior of the learning module on randomly-generated examples.

Khatib, Lina↗
NASA NTRS2001

Reasoning abstractly about resources

r describes a way to schedule high level activities before distributing them across multiple rovers in order to coordinate the resultant use of shared resources regardless of how each rover decides how to perform its activities. We present an algorithm for summarizing the metric resource requirements of an abstract activity based n the resource usages of its potential refinements.

abstraction planning rovers multiple agents↗
NASA NTRS2008

Automated Assume-Guarantee Reasoning by Abstraction Refinement

Current automated approaches for compositional model checking in the assume-guarantee style are based on learning of assumptions as deterministic automata. We propose an alternative approach based on abstraction refinement. Our new method computes the assumptions for the assume-guarantee rules as conservative and not necessarily deterministic abstractions of some of the components, and refines those abstractions using counter-examples obtained from model checking them together with the other components. Our approach also exploits the alphabets of the interfaces between components and performs iterative refinement of those alphabets as well as of the abstractions. We show experimentally that our preliminary implementation of the proposed alternative achieves similar or better performance than a previous learning-based implementation.

Pasareanu, Corina S.↗
NASA NTRS2013

On a Formal Tool for Reasoning About Flight Software Cost Analysis

A report focuses on the development of flight software (FSW) cost estimates for 16 Discovery-class missions at JPL. The techniques and procedures developed enabled streamlining of the FSW analysis process, and provided instantaneous confirmation that the data and processes used for these estimates were consistent across all missions. The research provides direction as to how to build a prototype rule-based system for FSW cost estimation that would provide (1) FSW cost estimates, (2) explanation of how the estimates were arrived at, (3) mapping of costs, (4) mathematical trend charts with explanations of why the trends are what they are, (5) tables with ancillary FSW data of interest to analysts, (6) a facility for expert modification/enhancement of the rules, and (7) a basis for conceptually convenient expansion into more complex, useful, and general rule-based systems.

Spagnuolo, John N., Jr.↗
NASA NTRS2015

Diagnostic Reasoning using Prognostic Information for Unmanned Aerial Systems

With increasing popularity of unmanned aircraft, continuous monitoring of their systems, software, and health status is becoming more and more important to ensure safe, correct, and efficient operation and fulfillment of missions. The paper presents integration of prognosis models and prognostic information with the R2U2 (REALIZABLE, RESPONSIVE, and UNOBTRUSIVE Unit) monitoring and diagnosis framework. This integration makes available statistically reliable health information predictions of the future at a much earlier time to enable autonomous decision making. The prognostic information can be used in the R2U2 model to improve diagnostic accuracy and enable decisions to be made at the present time to deal with events in the future. This will be an advancement over the current state of the art, where temporal logic observers can only do such valuation at the end of the time interval. Usefulness and effectiveness of this integrated diagnostics and prognostics framework was demonstrated using simulation experiments with the NASA Dragon Eye electric unmanned aircraft.

Diagnostics↗
NASA NTRS2014

Addressing the Hard Factors for Command File Errors by Probabilistic Reasoning

Command File Errors (CFE) are managed using standard risk management approaches at the Jet Propulsion Laboratory. Over the last few years, more emphasis has been made on the collection, organization, and analysis of these errors for the purpose of reducing the CFE rates. More recently, probabilistic modeling techniques have been used for more in depth analysis of the perceived error rates of the DAWN mission and for managing the soft factors in the upcoming phases of the mission. We broadly classify the factors that can lead to CFE's as soft factors, which relate to the cognition of the operators and hard factors which relate to the Mission System which is composed of the hardware, software and procedures used for the generation, verification & validation and execution of commands. The focus of this paper is to use probabilistic models that represent multiple missions at JPL to determine the root cause and sensitivities of the various components of the mission system and develop recommendations and techniques for addressing them. The customization of these multi-mission models to a sample interplanetary spacecraft is done for this purpose.

Meshkat, Leila↗
NASA NTRS2000

Processing CCD Images to Detect Transits of Earth-Sized Planets: Maximizing Sensitivity While Achieving Reasonable Downlink Requirements

We have performed end-to-end laboratory and numerical simulations to demonstrate the capability of differential photometry under realistic operating conditions to detect transits of Earth-sized planets orbiting solar-like stars. Data acquisition and processing were conducted using the same methods planned for the proposed Kepler Mission. These included performing aperture photometry on large-format CCD images of an artificial star fields obtained without a shutter at a readout rate of 1 megapixel/sec, detecting and removing cosmic rays from individual exposures and making the necessary corrections for nonlinearity and shutterless operation in the absence of darks. We will discuss the image processing tasks performed `on-board' the simulated spacecraft, which yielded raw photometry and ancillary data used to monitor and correct for systematic effects, and the data processing and analysis tasks conducted to obtain lightcurves from the raw data and characterize the detectability of transits. The laboratory results are discussed along with the results of a numerical simulation carried out in parallel with the laboratory simulation. These two simulations demonstrate that a system-level differential photometric precision of 10-5 on five- hour intervals can be achieved under realistic conditions.

Earth-size planets↗
NASA NTRS2019

Air Mobility Data & Reasoning Fabric

Throughout the world, especially in dense urban environments, the quality of life is being negatively impacted by ever growing commute time. Travel, beyond commuting, is increasingly driven by door-to-door challenges ? not just gate-to-gate considerations. Air Mobility may be an approach to address these challenges, as it can effectively convert our 2D mobility system to a 3D mobility system, vastly increasing mobility options.

Van Dalsem, William R.↗
NASA NTRS2021

Defining and Reasoning about Model-based Safety Analysis: A Review

Model-based safety analysis (MBSA) has been around for over two decades. The benefits of MBSA have been well-documented in the literature, such as tackling complexity, introducing Formal Methods to eliminate the ambiguity in the traditional safety analysis, using automation to replace the error-prone manual safety modeling process, and ensuring consistency between the design model and the safety model. However, there is still a lack of consensus on what MBSA even is. This paper provides an approach towards developing such a consensus

model-based↗