Jennifer L. Rhatigan

Bio: Jennifer L. Rhatigan is an academic researcher from Glenn Research Center. The author has contributed to research in topics: International Space Station & Scientific research on the International Space Station. The author has an hindex of 6, co-authored 21 publications receiving 163 citations. Previous affiliations of Jennifer L. Rhatigan include North Carolina State University.

Gas-phase radiative effects on the burning and extinction of a solid fuel

Abstract: Gas-phase radiative effects on the burning and extinction of a solid fuel in a stagnation-point flow geometry are investigated using a statistical narrow-band model with carbon dioxide and water vapor as the radiative participating media. The model, coupled to other flame conservation equations with a one-step overall gas-phase chemical reaction and Arrhenius solid pyrolysis relation, is solved numerically. Flame temperature, solid burning rate, and heat fluxes are examined as functions of stretch rate. Using ambient oxygen percentage and stretch rate as coordinates, A U-shaped extinction boundary is identified. The extinction behavior at low stretch rates is qualitatively similar to that predicted by earlier theory with only surface radiation loss. However, gas radiation introduces additional heat loss from the system and shrinks the solid flammable domain. In addition, gas radiation can cause a substantial decrease of flame temperature and constitutes a significant portion of the heat feedback to the solid at low stretch rates. In the second part of the paper, a computationally less intensive gray gas radiation model is tested. As with a number of earlier investigations, the use of Planck mean absorption coefficient is found to overpredict net emission and flame radiative loss. By multiplying a correction factor (less than 1) in front of the Planck mean absorption coefficient, it is possible to compute many global flame properties with reasonable accuracy. An empirically determined formula is given to find the value of this correction factor for a given flame. This is offered as an engineering approach for the flame radiation treatment.

International Space Station Science Research Accomplishments During the Assembly Years: An Analysis of Results from 2000-2008

Abstract: This report summarizes research accomplishments on the International Space Station (ISS) through the first 15 Expeditions. When research programs for early Expeditions were established, five administrative organizations were executing research on ISS: bioastronautics research, fundamental space biology, physical science, space product development, and space flight. The Vision for Space Exploration led to changes in NASA's administrative structures, so we have grouped experiments topically by scientific themes human research for exploration, physical and biological sciences, technology development, observing the Earth, and educating and inspiring the next generation even when these do not correspond to the administrative structure at the time at which they were completed. The research organizations at the time at which the experiments flew are preserved in the appendix of this document. These investigations on the ISS have laid the groundwork for research planning for Expeditions to come. Humans performing scientific investigations on ISS serve as a model for the goals of future Exploration missions. The success of a wide variety of investigations is an important hallmark of early research on ISS. Of the investigations summarized here, some are completed with results released, some are completed with preliminary results, and some remain ongoing.

Exploration-Related Research on ISS: Connecting Science Results to Future Missions

Abstract: In January, 2004, the U.S. President announced The Vision for Space Exploration, and charged the National Aeronautics and Space Administration (NASA) with using the International Space Station (ISS) for research and technology targeted at supporting U.S. space exploration goals. This paper describes: What we have learned from the first four years of research on ISS relative to the exploration mission; The on-going research being conducted in this regard; and Our current understanding of the major exploration mission risks that the ISS can be used to address. Specifically, we discuss research carried out on the ISS to determine the mechanisms by which human health is affected on long-duration missions, and to develop countermeasures to protect humans from the space environment. These bioastronautics experiments are key enablers of future long duration human exploration missions. We also discuss how targeted technological developments can enable mission design trade studies. We discuss the relationship between the ultimate number of human test subjects available on the ISS to the quality and quantity of scientific insight that can be used to reduce health risks to future explorers. We discuss the results of NASA's efforts over the past year to realign the ISS research programs to support a product-driven portfolio that is directed towards reducing the major risks of exploration missions. The fundamental challenge to science on ISS is completing experiments that answer key questions in time to shape design decisions for future exploration. In this context, exploration relevant research must do more than be conceptually connected to design decisions - it must become a part of the mission design process.

On solid trioxane combustion in stagnation point flows

Abstract: Response, flame structure, and extinction limits of solid trioxane (C 3 H 6 O 3 ) combustion in stagnationpointflows are computationally studied with detailed chemistry, transport properties, and radiation representation. While a solid surface radiation model addresses emission and absorption by the surface, a narrowband radiation model, with carbon dioxide, carbon monoxide, and water vapor as the gas-phase participating media, is employed to describe the gas-phase and surface radiation is presented over the flammable regime, with emphasis on the low-stretch regine of the radiatively participating flames. When only surface radiation is included, two extinction limits exist, namely the blow-off limit and the low-stretch radiative limit, and the burning rates and maximum flame temperatures are lower than those of the adiabatic counterpart, as expected. With the inclusion of surface and gas-phase radiation, results show that, while flame temperatures are even lower, the burning rate of the trioxane diffusion flame may actually exceed the adiabatic limit and increase at low stretch rate due to radiative feedback from the flame to the surface. Reaction pathways leading to trioxane oxidation are also analyzed. High-temperature and lowtemperature reaction pathways identified previously in homogeneous kinetics studies are sustained in heterogeneous trioxane combustion. Furthermore, potential effects of radical recombination at the solid surface are assessed and discussed.

Recent research accomplishments on the International Space Station

Abstract: Astronauts have conducted more than four years of continuous space research aboard the International Space Station (ISS). The US laboratory module, Destiny, is outfitted with a robust suite of scientific equipment to support spaceflight research. Research, albeit limited, is ongoing in spite the grounding of the Space Shuttle fleet as a result of the loss of the Columbia in February 2003. Results from the last four years of research on ISS are now appearing in the scientific literature. Indeed, scientific articles are now being submitted to peer-reviewed journals from the ISS by the Science Officer on board. This paper addresses the recent research results and accomplishments; and discusses the unique challenges faced in these early years of ISS assembly, including the methods for conduct of research while the Space Shuttle is unavailable as a resource for deploying and returning experiments for the ISS. We also discuss how the research portfolio is being realigned to support the use of ISS to enable NASA's Exploration Mission.

Progress in knowledge of flamelet structure and extinction

Abstract: In the past 25 years there has been a considerable amount of progress in studying flamelets, their structures and their responses to various perturbations. The term “flamelet” as used here really would mean “laminar flame” to most readers and is employed only because a major motivation is for ultimate use in connection with more complex flows, mainly turbulent. There is, however, no consideration here of how the knowledge reviewed may be employed in flamelet modeling of turbulent combustion. Not even time-dependent flamelets are addressed, although a few related references are provided. The focus is narrower, namely on quasisteady flamelets, and therefore the considerations of flamelet extinction that are presented concern quasisteady extinction, that is, not the dynamics of extinction. Even in this narrow context, it will be seen that a great deal has been accomplished. When such a long-term view is taken, it is found remarkable how much progress has been made. The progress is addressed separately for premixed, nonpremixed and partially premixed systems. Suggested directions of future research also are indicated. Despite the limited scope of the topic and the extensive advancement that has occurred, much more research remains to be done.

Review and analysis of over 40 years of space plant growth systems.

Abstract: The cultivation of higher plants occupies an essential role within bio-regenerative life support systems. It contributes to all major functional aspects by closing the different loops in a habitat like food production, CO2 reduction, O2 production, waste recycling and water management. Fresh crops are also expected to have a positive impact on crew psychological health. Plant material was first launched into orbit on unmanned vehicles as early as the 1960s. Since then, more than a dozen different plant cultivation experiments have been flown on crewed vehicles beginning with the launch of Oasis 1, in 1971. Continuous subsystem improvements and increasing knowledge of plant response to the spaceflight environment has led to the design of Veggie and the Advanced Plant Habitat, the latest in the series of plant growth systems. The paper reviews the different designs and technological solutions implemented in higher plant flight experiments. Using these analyses a comprehensive comparison is compiled to illustrate the development trends of controlled environment agriculture technologies in bio-regenerative life support systems, enabling future human long-duration missions into the solar system.

Meteoroid/Debris Shielding

Abstract: This report provides innovative, low-weight shielding solutions for spacecraft and the ballistic limit equations that define the shield's performance in the meteoroid/debris environment. Analyses and hypervelocity impact testing results are described that have been used in developing the shields and equations. Spacecraft shielding design and operational practices described in this report are used to provide effective spacecraft protection from meteoroid and debris impacts. Specific shield applications for the International Space Station (ISS), Space Shuttle Orbiter and the CONTOUR (Comet Nucleus Tour) space probe are provided. Whipple, Multi-Shock and Stuffed Whipple shield applications are described.

A review of scuffing models

Abstract: The mechanism of wear known as scuffing has been a research topic of great interest for many years. However, the question of how scuffing is initiated and the factors that contribute to its occurrence are still poorly understood. In general, it can be said that scuffing manifests itself as the sudden failure of lubricating films in mechanical equipment operating under extreme conditions of load and/or speed. Components such as cams, tappets, gears and piston rings are all prone to scuffing failure. Understanding the mechanisms that initiate failure would enable the development of criteria for scuffing prediction. This paper reviews the numerous scuffing models and theories that exist today and, in doing so, defines the important factors involved in scuffing initiation. Emphasis is given to existing theoretical scuffing models which have been correlated by a wealth of research data obtained from experimental test rigs.

Understanding combustion processes through microgravity research

Abstract: A review of research on the effects of gravity on combustion processes is presented, with an emphasis on a discussion of the ways in which reduced-gravity experiments and modeling has led to new understanding. Comparison of time scales shows that the removal of buoyancy-induced convection leads to manifestations of other transport mechanisms, notably radiative heat transfer and diffusional processes such as Lewis number effects. Examples from premixed-gas combustion, non-premixed gas-jet flames, droplet combustion, flame spread over solid and liquid fuels, and other fields are presented. Promising directions for new research are outlined, the most important of which is suggested to be radiative reabsorption effects in weakly burning flames.