Growth of a mat-forming photograph in the presence of UV radiation

Knowledge of the survival and growth of microorganisms in the presence of ultraviolet radiation is important for understanding the potential for life to exist in environments exposed to high fluxes of UV radiation. The growth of a mat-forming phototrophic prokaryote, Chloroflexus aurantiacus, was examined in the presence of continuous high UV irradiation under otherwise optimal growth conditions. Evidence was sought for an intrinsic ability to grow in the presence of UV radiation in a carefully chosen organism known to be unusually resistant to UV radiation, of ancient lineage among the phototrophs, to resemble ancient microfossils from the Precambrian, and to be a mat-former. It was assumed that even a high intrinsic UV resistance would be inadequate for survival and growth in the presence of very high UV fluxes, and iron (Fe3+) was selected as a common, abundant UV-absorbing substance that might protest microorganisms growing in or under iron-bearing sediments. The effectiveness of Fe(3+) was tested as a UV protective agent at low concentrations in thin layers. It was concluded that intrinsic UV resistance in some organisms may account for growth, not just survival, of these organisms when exposed to high UV fluxes under otherwise optimal growth conditions in an anoxic environment. It was also concluded that Fe(3+) bearing sediments of 1 mm or less in thickness may provide an adequate shield against high UV fluxes permitting the growth of microorganisms just below their surface. As long as growth conditions were met, then the evolution and development of microorganisms would not be hampered by high UV fluxes impinging upon the surface of iron-bearing sediments

Buoyancy Effects on Concurrent Flame Spread Over Thick PMMA

The flammability of combustible materials in a spacecraft is important for fire safety applications because the conditions in spacecraft environments differ from those on earth. Experimental testing in space is difficult and expensive. However, reducing buoyancy by decreasing ambient pressure is a possible approach to simulate on-earth the burning behavior inside spacecraft environments. The objective of this work is to determine that possibility by studying the effect of pressure on concurrent flame spread, and by comparison with microgravity data, observe up to what point low-pressure can be used to replicate flame spread characteristics observed in microgravity. Specifically, this work studies the effect of pressure and microgravity on upward/concurrent flame spread over 10 mm thick polymethyl methacrylate (PMMA) slabs. Experiments in normal gravity were conducted over pressures ranging between 100 and 40 kPa and a forced flow velocity of 200 mm/s. Microgravity experiments were conducted during NASAs Spacecraft Fire Experiment (Saffire II), on board the Cygnus spacecraft at 100 kPa with an air flow velocity of 200 mm/s. Results show that reductions of pressure slow down the flame spread over the PMMA surface approaching that in microgravity. The data is correlated in terms of a non-dimensional mixed convection analysis that describes the convective heat transferred from the flame to the solid, and the primary mechanism controlling the spread of the flame. The extrapolation of the correlation to low pressures predicts well the flame spread rate obtained in microgravity in the Saffire II experiments. Similar results were obtained by the authors with similar experiments with a thin composite cotton/fiberglass fabric (published elsewhere). Both results suggest that reduced pressure can be used to approximately replicate flame behavior of untested gravity conditions for the burning of thick and thin solids. This work could provide guidance for potential ground-based testing for fire safety design in spacecraft and space habitats

On Simulating Concurrent Flame Spread in Reduced Gravity by Reducing Ambient Pressure

The flammability of combustible materials in spacecraft environments is of importance for fire safety applications because the environmental conditions can greatly differ from those on earth, and a fire in a spacecraft could be catastrophic. Moreover, experimental testing in spacecraft environments can be difficult and expensive, so using ground-based tests to inform microgravity tests is vital. Reducing buoyancy effects by decreasing ambient pressure is a possible approach to simulate a spacecraft environment on earth. The objective of this work is to study the effect of pressure on material flammability, and by comparison with microgravity data, determine the extent to which reducing pressure can be used to simulate reduced gravity. Specifically, this work studies the effect of pressure and microgravity on upward/concurrent flame spread rates and flame appearance of a burning thin composite fabric made of 75% cotton and 25% fiberglass (Sibal). Experiments in normal gravity were conducted using pressures ranging between 100 and 30 kPa and a forced flow velocity of 20 cm/s. Microgravity experiments were conducted during NASAs Spacecraft Fire Experiment (Saffire), on board of the Orbital Corporation Cygnus spacecraft at 100 kPa and an air flow velocity of 20 cm/s. Results show that reductions of ambient pressure slow the flame spread over the fabric. As pressure is reduced, flame intensity is also reduced. Comparison with the concurrent flame spread rates in microgravity show that similar flame spread rates are obtained at around 30 kPa. The normal gravity and microgravity data is correlated in terms of a mixed convection non-dimensional parameter that describes the heat transferred from the flame to the solid surface. The correlation provides information about the similitudes of the flame spread process in variable pressure and reduced gravity environments, providing guidance for potential on-earth testing for fire safety design in spacecraft and space habitats

Technology Development for Fire Safety in Exploration Spacecraft and Habitats

Fire during an exploration mission far from Earth is a particularly critical risk for exploration vehicles and habitats. The Fire Prevention, Detection, and Suppression (FPDS) project is part of the Exploration Technology Development Program (ETDP) and has the goal to enhance crew health and safety on exploration missions by reducing the likelihood of a fire, or, if one does occur, minimizing the risk to the mission, crew, or system. Within the past year, the FPDS project has been formalized within the ETDP structure and has seen significant progress on its tasks in fire prevention, detection, and suppression. As requirements for Constellation vehicles and, specifically, the CEV have developed, the need for the FPDS technologies has become more apparent and we continue to make strides to infuse them into the Constellation architecture. This paper describes the current structure of the project within the ETDP and summarizes the significant programmatic activities. Major technical accomplishments are identified as are activities planned for FY07

Effects of ambient gas density on the structure of pressure-atomizedsprays

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77110/1/AIAA-1991-690-582.pd

Determination of Realistic Fire Scenarios in Spacecraft

This paper expands on previous work that examined how large a fire a crew member could successfully survive and extinguish in the confines of a spacecraft. The hazards to the crew and equipment during an accidental fire include excessive pressure rise resulting in a catastrophic rupture of the vehicle skin, excessive temperatures that burn or incapacitate the crew (due to hyperthermia), carbon dioxide build-up or accumulation of other combustion products (e.g. carbon monoxide). The previous work introduced a simplified model that treated the fire primarily as a source of heat and combustion products and sink for oxygen prescribed (input to the model) based on terrestrial standards. The model further treated the spacecraft as a closed system with no capability to vent to the vacuum of space. The model in the present work extends this analysis to more realistically treat the pressure relief system(s) of the spacecraft, include more combustion products (e.g. HF) in the analysis and attempt to predict the fire spread and limiting fire size (based on knowledge of terrestrial fires and the known characteristics of microgravity fires) rather than prescribe them in the analysis. Including the characteristics of vehicle pressure relief systems has a dramatic mitigating effect by eliminating vehicle overpressure for all but very large fires and reducing average gas-phase temperatures

The Spacecraft Fire Experiment (Saffire) - Objectives, Development and Status

Since 2012, the Spacecraft Fire Experiment (Saffire) has been under development by the Spacecraft Fire Safety Demonstration (SFS Demo) project that is funded by NASA's Advanced Exploration Systems Division in the Human Exploration and Operations Mission Directorate. The overall objective of this project is to reduce the uncertainty and risk associated with the design of spacecraft fire safety systems for NASA's exploration missions. This is accomplished by defining, developing, and conducting experiments that address gaps in spacecraft fire safety knowledge and capabilities identified by NASA's Fire Safety System Maturation Team. This paper describes the three Spacecraft Fire Experiments (Saffire-I, -II, and -III) that were developed at NASA-GRC and that will conduct a series of material flammability tests in low-gravity and at length scales that are realistic for a spacecraft fire. The experiments will be conducted in Orbital ATK's Cygnus vehicle after it has unberthed from the International Space Station. The tests will be fully automated with the data downlinked at the conclusion of the test and before the Cygnus vehicle reenters the atmosphere. The objectives of these experiments are to (1) determine how rapidly a large scale fire grows in low-gravity and (2) investigate the low-g flammability limits compared to those obtained in NASA's normal gravity material flammability screening test. The hardware for these experiments has been completed and is awaiting their respective launches, all planned for 2016. This paper will review the objectives of these experiments and how they address several of the knowledge gaps for NASA's exploration missions. The hardware development will be discussed including several novel approaches that were taken for testing and evaluation of these series payloads. The status of the missions and operational status will also be presented

Effects of gas density on the structure of liquid jets in still gases

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77334/1/AIAA-11098-570.pd

Microgravity Flame Spread in Exploration Atmospheres: Pressure, Oxygen, and Velocity Effects on Opposed and Concurrent Flame Spread

Microgravity tests of flammability and flame spread were performed in a low-speed flow tunnel to simulate spacecraft ventilation flows. Three thin fuels were tested for flammability (Ultem 1000 (General Electric Company), 10 mil film, Nomex (Dupont) HT90-40, and Mylar G (Dupont) and one fuel for flame spread testing (Kimwipes (Kimberly-Clark Worldwide, Inc.). The 1g Upward Limiting Oxygen Index (ULOI) and 1g Maximum Oxygen Concentration (MOC) are found to be greater than those in 0g, by up to 4% oxygen mole fraction, meaning that the fuels burned in 0g at lower oxygen concentrations than they did using the NASA Standard 6001 Test 1 protocol. Flame spread tests with Kimwipes were used to develop correlations that capture the effects of flow velocity, oxygen concentration, and pressure on flame spread rate. These correlations were used to determine that over virtually the entire range of spacecraft atmospheres and flow conditions, the opposed spread is faster, especially for normoxic atmospheres. The correlations were also compared with 1g MOC for various materials as a function of pressure and oxygen. The lines of constant opposed flow agreed best with the 1g MOC trends, which indicates that Test 1 limits are essentially dictated by the critical heat flux for ignition. Further evaluation of these and other materials is continuing to better understand the 0g flammability of materials and its effect on the oxygen margin of safety