Jennifer L. Rhatigan

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.

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

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 NASAs 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

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

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 NASAs Exploration Mission.

NASA's Constellation Program: The final word

NASAs Constellation Program, formulated in 2005 to achieve the objectives of maintaining American presence in low Earth orbit, returning to the Moon for purpose of establishing an outpost, and exploring Mars and beyond in the first half of the 21st century, was cancelled in 2010 [US Congress, NASA Authorization Act, Public Law 11-267, 2010]. This paper describes the lessons learned developed by the staff of the Constellation Program to advise future programs, as well as program and system engineering managers of similar national efforts. These lessons learned are offered by those who experienced the day-to-day challenges of managing an effort planned as a multidecade undertaking. This effort spanned all 10 NASA Centers, multiple large-scale acquisitions, and required modernizing an infrastructure designed and sized largely for the Apollo program in the 1960s. Moreover, it required leading a workforce generationally removed from the previous human spacecraft launch and entry development challenges. Key lessons learned from the Constellation Program are addressed and cover program elements in which systems engineers provide leadership and/or assistance to program management, including program planning, requirements development, system design methodology, management structure, decision-making, and communications in a national program. ©2012 Wiley Periodicals, Inc. Syst Eng 16: