Spacecraft Fire Safety 1956 to 1999: An Annotated Bibliography

Knowledge of fire safety in spacecraft has resulted from over 50 years of investigation and experience in space flight. Current practices and procedures for the operation of the Space Transportation System (STS) shuttle and the International Space Station (ISS) have been developed from this expertise, much of which has been documented in various reports. Extending manned space exploration from low Earth orbit to lunar or Martian habitats and beyond will require continued research in microgravity combustion and fire protection in low gravity. This descriptive bibliography has been produced to document and summarize significant work in the area of spacecraft fire safety that was published between 1956 and July 1999. Although some important work published in the late 1990s may be missing, these citations as well as work since 2000 can generally be found in Web-based resources that are easily accessed and searched. In addition to the citation, each reference includes a short description of the contents and conclusions of the article. The bibliography contains over 800 citations that are cross-referenced both by topic and the authors and editors. There is a DVD that accompanies this bibliography (available by request from the Center for Aerospace Information) containing the full-text articles of selected citations as well as an electronic version of this report that has these citations as active links to their corresponding full-text article

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

Carbon Dioxide Dispersion in the Combustion Integrated Rack Simulated Numerically

When discharged into an International Space Station (ISS) payload rack, a carbon dioxide (CO2) portable fire extinguisher (PFE) must extinguish a fire by decreasing the oxygen in the rack by 50 percent within 60 sec. The length of time needed for this oxygen reduction throughout the rack and the length of time that the CO2 concentration remains high enough to prevent the fire from reigniting is important when determining the effectiveness of the response and postfire procedures. Furthermore, in the absence of gravity, the local flow velocity can make the difference between a fire that spreads rapidly and one that self-extinguishes after ignition. A numerical simulation of the discharge of CO2 from PFE into the Combustion Integrated Rack (CIR) in microgravity was performed to obtain the local velocity and CO2 concentration. The complicated flow field around the PFE nozzle exits was modeled by sources of equivalent mass and momentum flux at a location downstream of the nozzle. The time for the concentration of CO2 to reach a level that would extinguish a fire anywhere in the rack was determined using the Fire Dynamics Simulator (FDS), a computational fluid dynamics code developed by the National Institute of Standards and Technology specifically to evaluate the development of a fire and smoke transport. The simulation shows that CO2, as well as any smoke and combustion gases produced by a fire, would be discharged into the ISS cabin through the resource utility panel at the bottom of the rack. These simulations will be validated by comparing the results with velocity and CO2 concentration measurements obtained during the fire suppression system verification tests conducted on the CIR in March 2003. Once these numerical simulations are validated, portions of the ISS labs and living areas will be modeled to determine the local flow conditions before, during, and after a fire event. These simulations can yield specific information about how long it takes for smoke and combustion gases produced by a fire to reach a detector location, how large the fire would be when the detector alarms, and the behavior of the fire until it has been extinguished. This new capability could then be used to optimize the location of fire detectors and fire-suppression ports as well as to evaluate the effectiveness of fire suppressants and response strategies. Numerical data collected from these simulations could also be used to develop a virtual reality fire event for crew training and fire safety awareness. This work is funded by NASA's Bioastronautics Initiative, which has the objective of ensuring and enhancing the health, safety, and performance of humans in space. As part of this initiative, the Microgravity Combustion Science Branch at the NASA Glenn Research Center is conducting spacecraft fire safety research to significantly improve fire safety on inhabited spacecraft

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

Scaling Methods for Simulating Aircraft In-Flight Icing Encounters

This paper discusses scaling methods which permit the use of subscale models in icing wind tunnels to simulate natural flight in icing. Natural icing conditions exist when air temperatures are below freezing but cloud water droplets are super-cooled liquid. Aircraft flying through such clouds are susceptible to the accretion of ice on the leading edges of unprotected components such as wings, tailplane and engine inlets. To establish the aerodynamic penalties of such ice accretion and to determine what parts need to be protected from ice accretion (by heating, for example), extensive flight and wind-tunnel testing is necessary for new aircraft and components. Testing in icing tunnels is less expensive than flight testing, is safer, and permits better control of the test conditions. However, because of limitations on both model size and operating conditions in wind tunnels, it is often necessary to perform tests with either size or test conditions scaled. This paper describes the theoretical background to the development of icing scaling methods, discusses four methods, and presents results of tests to validate them

Users Manual for the NASA Lewis Ice Accretion Prediction Code (LEWICE)

LEWICE is an ice accretion prediction code that applies a time-stepping procedure to calculate the shape of an ice accretion. The potential flow field is calculated in LEWICE using the Douglas Hess-Smith 2-D panel code (S24Y). This potential flow field is then used to calculate the trajectories of particles and the impingement points on the body. These calculations are performed to determine the distribution of liquid water impinging on the body, which then serves as input to the icing thermodynamic code. The icing thermodynamic model is based on the work of Messinger, but contains several major modifications and improvements. This model is used to calculate the ice growth rate at each point on the surface of the geometry. By specifying an icing time increment, the ice growth rate can be interpreted as an ice thickness which is added to the body, resulting in the generation of new coordinates. This procedure is repeated, beginning with the potential flow calculations, until the desired icing time is reached. The operation of LEWICE is illustrated through the use of five examples. These examples are representative of the types of applications expected for LEWICE. All input and output is discussed, along with many of the diagnostic messages contained in the code. Several error conditions that may occur in the code for certain icing conditions are identified, and a course of action is recommended. LEWICE has been used to calculate a variety of ice shapes, but should still be considered a research code. The code should be exercised further to identify any shortcomings and inadequacies. Any modifications identified as a result of these cases, or of additional experimental results, should be incorporated into the model. Using it as a test bed for improvements to the ice accretion model is one important application of LEWICE

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

Portable Multigas Monitors for International Space Station

The Environmental Health System (EHS) on International Space Station (ISS) includes portable instruments to measure various cabin gases that acutely impact crew health. These hand-held devices measure oxygen, carbon dioxide, carbon monoxide, hydrogen chloride and hydrogen cyanide. The oxygen and carbon dioxide units also serve to back up key functions of the Major Constituent Analyzers. Wherever possible, commercial off-the-shelf (COTS) devices are employed by EHS to save development and sustaining costs. COTS hardware designed for general terrestrial applications however has limitations such as no pressure compensation, limited life of the active sensor, calibration drift, battery issues, unpredictable vendor support and obsolescence. The EHS fleet (inflight and ground inventory) of instruments is both aging and dwindling in number. With the retirement of the US Space Shuttle, maintenance of on-orbit equipment becomes all the more difficult. A project is underway to search for gas monitoring technology that is highly reliable and stable for years. Tunable Diode Laser Spectroscopy (TDLS) seems to be the front-runner technology, but generally is not yet commercially available in portable form. NASA has fostered the development of TDLS through the Small Business Innovative Research (SBIR) program. A number of gases of interest to the aerospace and submarine communities can be addressed by TDLS including the list mentioned above plus hydrogen fluoride, ammonia and water (humidity). There are several different forms of TDLS including photoacoustic and direct absorption spectroscopy using various multipass cell geometries. This paper describes the history of portable gas monitoring on NASA spacecraft and provides a status of the development of TDLS based instruments. Planned TDLS flight experiments on ISS could lead both to operational use on ISS and important roles in future Exploration spacecraft and habitats

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