R K Tripathi

NASA, Washington, WV, United States

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Publications (139)74.85 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Following the Columbia Accident Investigation Board report, the NASA Administrator chartered an executive team (known as the Diaz Team) to identify those report elements with NASA-wide applicability and to develop corrective measures to address each element. One such measure was the development of a standard for the development, documentation, and operation of models and simulations. The resulting standard attempts to develop a general framework for communicating information to decision makers by including programmatic, documentation, and reporting requirements. It also includes a scale intended to measure the credibility associated with model and simulation results. This report describes the philosophy and requirements overview of the resulting NASA Standard for Models and Simulations.
    Journal of Aircraft 01/2013; 50(1):20. · 0.63 Impact Factor
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    ABSTRACT: Exposures from the hazards of space radiation in deep space/long duration missions are very different from that of low earth orbit, and much needs to be learned about their effects. The overall situation is further augmented by the nonexistence of in vivo or in vitro data or studies about continuous long duration tissues exposure to radiation and concomitant biological uncertainties. All radiation protection and shielding transport and needed nuclear cross sections models so far have focused on radiation that goes through the shielding materials and are usually high energy physics models. From the perspective of exposure to astronauts, this exposure contributes to health risks. However, the very important radiation exposure where the radiation traverses through the astronauts and considerably slows down and/or even stops inside their body is less well studied. This kind of radiation contributes may be more biologically damaging than the radiation which just passes through because the ionizing power is highest as the particle stops in tissue. There is a clear need for improved nuclear physics cross sections models to described low energy collisions. Low energy physics significantly contributes to biological dose, risk assessments, and related uncertainty evaluations. In this report we will focus on the current status of these (mostly low energy) cross sections models and elaborate on future directions.
    07/2012;
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    ABSTRACT: To meet the challenge of future deep space programs, an accurate and efficient engineering code for analyzing the shielding requirements against high-energy galactic heavy ion radiation is needed. In consequence, a new version of the HZETRN code capable of simulating high charge and energy (HZE) ions with either laboratory or space boundary conditions is currently under development. This code, GRNTRN, is based on a Green’s function approach to the solution of the one-dimensional Boltzmann transport equation and like its predecessor is deterministic in nature. The computational model consists of the lowest order asymptotic approximation followed by a Neumann series expansion with non-perturbative corrections. The physical description includes energy loss with straggling, nuclear attenuation, nuclear fragmentation with energy dispersion and down shift. Code validation in the laboratory environment is addressed by showing that GRNTRN accurately predicts energy loss spectra as measured by solid-state detectors in ion beam experiments with multi-layer targets. In order to verify and benchmark the code with space boundary conditions, measured particle fluxes are propagated through several thicknesses of shielding using both GRNTRN and the current version of HZETRN. The favorable agreement obtained indicates that GRNTRN accurately models the propagation of HZE ions in laboratory settings. It also compares very well with the extensively validated space environment HZETRN code and thus provides verification of the HZETRN propagator.
    Advances in Space Research 01/2011; · 1.18 Impact Factor
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    ABSTRACT: The protection of astronauts and instrumentation from galactic cosmic rays and solar particle events is one of the primary constraints associated with mission planning in low earth orbit or deep space. To help satisfy this constraint, several computational tools have been developed to analyze the effectiveness of various shielding materials and structures exposed to space radiation. These tools are now being carefully scrutinized through a systematic effort of verification, validation, and uncertainty quantification. In this benchmark study, the deterministic transport code HZETRN is compared to the Monte Carlo transport codes HETC-HEDS and FLUKA for a 30 g/cm2 water target protected by a 20 g/cm2 aluminum shield exposed to a parameterization of the February 1956 solar particle event. Neutron and proton fluences as well as dose and dose equivalent are compared at various depths in the water target. The regions of agreement and disagreement between the three codes are quantified and discussed, and recommendations for future work are given.
    Advances in Space Research 01/2011; · 1.18 Impact Factor
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    ABSTRACT: The HZETRN deterministic radiation code is one of several tools developed to analyze the effects of harmful galactic cosmic rays (GCR) and solar particle events on mission planning and shielding for astronauts and instrumentation. This paper is a comparison study involving the two Monte Carlo transport codes, HETC–HEDS and FLUKA and the deterministic transport code, HZETRN. Each code is used to transport an ion from the 1977 solar minimum GCR spectrum impinging upon a 20 g/cm2 aluminum slab followed by a 30 g/cm2 water slab. This research is part of a systematic effort of verification and validation to quantify the accuracy of HZETRN and determine areas where it can be improved. Comparisons of dose and dose equivalent values at various depths in the water slab are presented in this report. This is followed by a comparison of the proton and forward, backward and total neutron flux at various depths in the water slab. Comparisons of the secondary light ion 2H, 3H, 3He and 4He fluxes are also examined.
    Advances in Space Research 01/2011; · 1.18 Impact Factor
  • Advances in Geosciences, Volume 19: Planetary Science (SE). 05/2010;
  • Advances in Geosciences, Volume 19: Planetary Science (SE). 05/2010;
  • LPI Contributions. 10/2008;
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    R.K. Tripathi, J.E. Nealy
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    ABSTRACT: NASA is now focused on the agency's vision for space exploration encompassing a broad range of human and robotic missions including missions to Moon, Mars and beyond. As a result, there is a focus on long duration space missions. NASA is committed to the safety of the missions and the crew, and there is an overwhelming emphasis on the reliability issues for space missions and the habitat. The cost-effective design of the spacecraft demands a very stringent requirement on the optimization process. Exposure from the hazards of severe space radiation in deep space and/or long duration missions is a critical design constraint and a potential 'show stopper.' Thus, protection from the hazards of severe space radiation is of paramount importance to the agency's vision. It is envisioned to have long duration human presence on the Moon for deep space exploration. The exposures from ionizing radiation - galactic cosmic radiation and solar particle events - and optimized shield design for a swing-by and a long duration Mars mission have been investigated. It is found that the technology of today is inadequate for safe human missions to Mars, and revolutionary technologies need to be developed for long duration and/or deep space missions. The study will provide a guideline for radiation exposure and protection for long duration missions and career astronauts and their safety.
    Aerospace Conference, 2008 IEEE; 04/2008
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    R.K. Tripathi, J.E. Nealy
    [Show abstract] [Hide abstract]
    ABSTRACT: NASA is now focused on the agency's vision for space exploration encompassing a broad range of human and robotic missions including missions to Moon, Mars and beyond. As a result, there is a focus on long duration space missions. NASA is committed to the safety of the missions and the crew, and there is an overwhelming emphasis on the reliability issues for space missions and the habitat. The cost effective design of the spacecraft demands a very stringent requirement on the optimization process. Exposure from the hazards of severe space radiation in deep space and/or long duration missions is a critical design constraint and a potential 'show stopper.' Thus, protection from the hazards of severe space radiation is of paramount importance to the agency's vision. It is envisioned to have long duration human presence on the Moon for deep space exploration. The exposures from ionizing radiation - galactic cosmic radiation and solar particle events - and optimized shield design for a short-term and a long-term mission to Moon have been investigated. It is found that the technology of today is adequate for short-term safe human missions to Moon, and revolutionary technologies need to be developed for long duration Moon missions and/or deep space missions. The study will provide a guideline for radiation exposure and protection for long duration missions and career astronauts and their safety.
    Aerospace Conference, 2008 IEEE; 04/2008
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    ABSTRACT: For long duration and/or deep space human missions, protection from severe space radiation exposure is a challenging design constraint and may be a potential limiting factor. The space radiation environment consists of galactic cosmic rays (GCR), solar particle events (SPE), trapped radiation, and includes ions of all the known elements over a very broad energy range. These ions penetrate spacecraft materials producing nuclear fragments and secondary particles that damage biological tissues, microelectronic devices, and materials. Accurate risk assessments critically depend on the accuracy of the input information about the interaction of ions with materials, electronics and tissues and the radiation transport codes. Due to complexity of the problem and paucity of huge amount of experimental data, it is prudent to benchmark leading radiation transport codes to build increasing confidence in exposure estimates. The deterministic code HZETRN2006, and the Monte Carlo Codes HETC-HEDS and FLUKA, are used for benchmarking efforts. The SPE Webber spectrum and 1977 GCR radiation environments has been taken to make radiation dose exposure studies on aluminum shield followed by water target.
    04/2008;
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    ABSTRACT: Models of the lunar radiation environment due to galactic cosmic rays (GCR) and solar particle events (SPE) have been developed. Results have been obtained for orbital, surface and subsurface scenarios and polar locations for volatile studies.
    03/2008;
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    ABSTRACT: For the success of NASA's new vision for space exploration to Moon, Mars and beyond, exposures from the hazards of severe space radiation in deep space long duration missions is ``a must solve'' problem. The exploration beyond low Earth orbit to enable routine access of space will require protection from the hazards of the accumulated exposures of space radiation. There is a need to look to new horizons for newer technologies. The present multidisciplinary investigation explores the feasibility of using the active electrostatic shielding in concert with the state-of-the-art materials shielding and protection technologies. The full space radiation environment has been used, for the first time, to explore the feasibility of multidisciplinary shielding. The goal is to repel enough positive charge ions so that they miss the spacecraft without attracting thermal electrons and further attenuate the exposure using nano-materials. Conclusions are drawn for the future directions of space radiation protection.
    03/2008;
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    ABSTRACT: To meet the challenge of future deep space programs, an accurate and efficient engineering code for analyzing the shielding requirements against high-energy galactic heavy radiation is needed. To address this need, a new Green's function code capable of simulating high charge and energy ions with either laboratory or space boundary conditions is currently under development. The computational model consists of combinations of physical perturbation expansions based on the scales of atomic interaction, multiple scattering, and nuclear reactive processes with use of the Neumann-asymptotic expansions with non-perturbative corrections. The code contains energy loss due to straggling, nuclear attenuation, nuclear fragmentation with energy dispersion and downshifts. Previous reports show that the new code accurately models the transport of ion beams through a single slab of material. Current research efforts are focused on enabling the code to handle multiple layers of material and the present paper reports on progress made towards that end.
    01/2008;
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    ABSTRACT: For long duration and/or deep space human missions, protection from severe space radiation exposure is a challenging design constraint and may be a potential limiting factor. The space radiation environment consists of galactic cosmic rays (GCR), solar particle events (SPE), trapped radiation, and includes ions of all the known elements over a very broad energy range. These ions penetrate spacecraft materials producing nuclear fragments and secondary particles that damage biological tissues, microelectronic devices, and materials. In deep space missions, where the Earth's magnetic field does not provide protection from space radiation, the GCR environment is significantly enhanced due to the absence of geomagnetic cut-off and is a major component of radiation exposure. Accurate risk assessments critically depend on the accuracy of the input information as well as radiation transport codes used, and so systematic verification of codes is necessary. In this study, comparisons are made between the deterministic code HZETRN2006 and the Monte Carlo codes HETC-HEDS and FLUKA for an aluminum shield followed by a water target exposed to the 1977 solar minimum GCR spectrum. Interaction and transport of high charge ions present in GCR radiation environment provide a more stringent constraint in the comparison of the codes. Dose, dose equivalent and flux spectra are compared; details of the comparisons will be discussed, and conclusions will be drawn for future directions.
    01/2008;
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    ABSTRACT: A scale is presented to evaluate the rigor of modeling and simulation (M&S) practices for the purpose of supporting a credibility assessment of the M&S results. The scale distinguishes required and achieved levels of rigor for a set of M&S elements that contribute to credibility including both technical and process measures. The work has its origins in an interest within NASA to include a “Credibility Assessment Scale” in development of a NASA standard for models and simulations.
    49th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials, Schaumburg, IL; 01/2008
  • [Show abstract] [Hide abstract]
    ABSTRACT: To meet the challenge of future deep space programs, an accurate and efficient engineering code for analyzing the shielding requirements against high-energy galactic heavy radiations is needed. In consequence, a new version of the HZETRN code capable of simulating high charge and energy (HZE) ions with either laboratory or space boundary conditions is currently under development. The new code, GRNTRN, is based on a Green's function approach to the solution of Boltzmann's transport equation and like its predecessor is deterministic in nature. The computational model consists of the lowest order asymptotic approximation followed by a Neumann series expansion with non-perturbative corrections. The physical description includes energy loss with straggling, nuclear attenuation, nuclear fragmentation with energy dispersion and down shift. Code validation in the laboratory environment is addressed by showing that GRNTRN accurately predicts energy loss spectra as measured by solid-state detectors in ion beam experiments with multi-layer targets. In order to validate the code with space boundary conditions, measured particle fluences are propagated through several thicknesses of shielding using both GRNTRN and the current version of HZETRN. The excellent agreement obtained indicates that GRNTRN accurately models the propagation of HZE ions in the space environment as well as in laboratory settings and also provides verification of the HZETRN propagator.
    01/2008;
  • [Show abstract] [Hide abstract]
    ABSTRACT: For the success of NASA's new vision for space exploration to Moon, Mars and beyond, exposures from the hazards of severe space radiation in deep space long duration missions is `a must solve' problem. The payload penalty demands a very stringent requirement on the design of the spacecrafts for human deep space missions. The exploration beyond low Earth orbit (LEO) to enable routine access of space will require protection from the hazards of the accumulated exposures of space radiation, Galactic Cosmic Rays (GCR) and Solar Particle Events (SPE), and minimizing the production of secondary radiation is a great advantage. There is a need to look to new horizons for newer technologies. The present investigation revisits electrostatic active radiation shielding and explores the feasibility of using the electrostatic shielding in concert with the state-of-the-art materials shielding and protection technologies. The full space radiation environment has been used, for the first time, to explore the feasibility of electrostatic shielding. The goal is to repel enough positive charge ions so that they miss the spacecraft without attracting thermal electrons. Conclusions are drawn for the future directions of space radiation protection.
    Advances in Space Research 01/2008; 42:1043-1049. · 1.18 Impact Factor
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    ABSTRACT: Software that is used for aerospace flight control and to display information to pilots and crew is expected to be correct and credible at all times. This type of software is typically developed under strict management processes, which are intended to reduce defects in the software product. However, modeling and simulation (M&S) software may exhibit varying degrees of correctness and credibility, depending on a large and complex set of factors. These factors include its intended use, the known physics and numerical approximations within the M&S, and the referent data set against which the M&S correctness is compared. The correctness and credibility of an M&S effort is closely correlated to the uncertainty management (UM) practices that are applied to the M&S effort. This paper describes an uncertainty structure matrix for M&S, which provides a set of objective descriptions for the possible states of UM practices within a given M&S effort. The columns in the uncertainty structure matrix contain UM elements or practices that are common across most M&S efforts, and the rows describe the potential levels of achievement in each of the elements. A practitioner can quickly look at the matrix to determine where an M&S effort falls based on a common set of UM practices that are described in absolute terms that can be applied to virtually any M&S effort. The matrix can also be used to plan those steps and resources that would be needed to improve the UM practices for a given M&S effort.
    49th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials, Schaumburg, IL; 01/2008
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    ABSTRACT: Results for the radiation environment to be found on the planet Mars due to Galactic Cosmic Rays (GCR) and Solar Particle Events (SPE) has been obtained. Primary particle environments computed for Martian conditions are transported within the Mars atmosphere, modeled in a time-dependent way in terms of density, pressure, and temperature vs. altitude, down to the surface, with topography and backscattering patterns taken into account. The atmospheric chemical and isotopic composition has been modeled over results from the in-situ Viking Lander measurements for both major and minor components. The surface topography has been determined by using a model based on the data provided by the Mars Orbiter Laser Altimeter (MOLA) instrument on board the Mars Global Surveyor (MGS) spacecraft. The surface itself has been modeled in both the dry (‘regolith’) and volatile components. Mars regolith composition has been modeled based on the measurements obtained with orbiter and lander spacecraft from which an average composition has been derived. The volatile inventory properties, both in the regolith and in the seasonal and perennial polar caps, has been taken into account by modeling the deposition of volatiles and its variations with geography and time all throughout the Martian year, from results from imaging data of orbiter spacecraft. Results are given in terms of fluxes, doses and LET, for most kinds of particles, namely protons, neutrons, alpha particles, heavy ions, pions, and muons for various soil compositions.
    Nuclear Physics B - Proceedings Supplements 04/2007; · 0.88 Impact Factor

Publication Stats

606 Citations
74.85 Total Impact Points

Institutions

  • 1998–2008
    • NASA
      • • Langley Research Center
      • • Radiation Biophysics Laboratory
      Washington, WV, United States
  • 1996–2008
    • Hampton VA Medical Center
      Hampton, Virginia, United States
    • University of California, Berkeley
      • Lawrence Berkeley Laboratory
      Berkeley, MO, United States
  • 1994–2007
    • Christopher Newport University
      Newport News, Virginia, United States
    • Newport University
      Newport News, Virginia, United States
  • 1993–2004
    • Old Dominion University
      • • Department of Mathematics and Statistics
      • • Department of Physics
      Norfolk, Virginia, United States
  • 1997–1999
    • Hampton University
      • Department of Physics
      Hampton, VA, United States
  • 1996–1998
    • Southern Illinois University Carbondale
      • Department of Physics
      Illinois, United States