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Fire Prevention, Detection, and Suppression Research Supporting Manned Space Exploration - One Year Later

Gary A. Ruff* and David L. Urban† NASA Glenn Research Center, Cleveland, OH 44135

Merrill K. King‡ NASA Headquarters, Washington DC

Fire during an exploration mission far from Earth is a particularly critical risk for exploration vehicles and habitats because, unlike in most scenarios here on Earth, escape is not an option and assistance may be weeks or months away. The goal of the Fire Prevention, Detection, and Suppression project is 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. The implementation of this project has been significantly impacted by the Vision for Space Exploration and, over the past year, has been re-focused to meet the current design and development schedule for the Crew Exploration Vehicle and the Lunar Surface Access Module. This paper describes the current deliverables for the FPDS project in the areas of fire prevention and material flammability, fire signatures and detection, and fire suppression and response. Tasks that are underway or planned to deliver these products are also presented, with the emphasis on updating the status of the work in each area.

I. Introduction he Vision for Space Exploration (VSE) announced by the President on January 14, 2004 directed NASA to retire the Space Shuttle by 2010, build and fly a new Crew Exploration Vehicle (CEV) no later than 2014, and return humans to the Moon by 2020. Lunar operations would then be used as a proving ground for technologies

required for the journey to and exploration of Mars and other destinations. While not explicitly stated at the time, successful implementation of the Vision would require significant technological advances in practically all facets of an exploration mission including propulsion systems, power generation and storage, dust mitigation, environmental control and life support, thermal controls, avionics and software, and in-situ resource utilization (ISRU), to name a few. It was also very clear that the performance standards required for these technologies were, in many cases, well beyond those used on the International Space Station (ISS) and the Space Transportation System (STS). The Fire Prevention, Detection, and Suppression (FPDS) program is one of these technology development areas, formerly tracked within the Life Support and Habitation (LSH) program of the Exploration System Missions Directorate (ESMD). The overarching goal for work in the FPDS area is 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. In 2005, Ruff et al.1 documented the objectives of the FPDS and presented a research plan that identified tasks to be performed in each core area, namely material flammability, fire detection, and fire suppression, to meet those objectives. This report described the products that would be delivered by the FPDS program to the ESMD that, when incorporated into the design of the vehicle and habitat systems, would provide quantifiable improvements in fire protection while minimizing system mass, complexity, and overall risk to the mission. In May 2005, NASA Administrator Griffin accelerated the first flight of the CEV from 2014 to 2011 and added the requirement that the CEV be capable of ferrying crew and cargo to and from the ISS. Subsequent analysis and definition of the crew and launch systems determined that, to meet this accelerated schedule within the specified budget, the flight systems must be developed with predominantly existing technology, thereby reducing planned expenditures in technology development for the initial CEV crew and launch systems. The completion of the Exploration Systems Architecture Study (ESAS) in September 2005 has re-directed NASA’s technology development efforts, now consolidated within the Exploration Technology Development Program managed through * FPDS Element Lead, NASA John H. Glenn Research Center/MS 77-5, AIAA Associate Fellow. † Branch Chief, Microgravity Combustion and Reacting Systems Branch, NASA John H. Glenn Research Center/MS 77-5, AIAA Member. ‡ FPDS Program Element Manager, NASA Headquarters, AIAA Fellow.

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44th AIAA Aerospace Sciences Meeting and Exhibit9 - 12 January 2006, Reno, Nevada

AIAA 2006-347

This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

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NASA Langley. In general, the technology development efforts were staged so the required technologies would be available when needed although much work was completely eliminated because the mission, as now defined, would be accomplished using currently available technologies. Since the release of the findings of the architecture study, the impact of the acceleration of the CEV development schedule on the FPDS project has been assessed. The purpose of this paper is to describe these impacts by reviewing the current objectives and deliverables of the FPDS project, as well as reporting the status of several of the major work efforts. The starting point for this status report is the research plan presented in 20051. For completeness, portions of the 2005 paper are repeated here, especially since most of the objectives and deliverables have remained intact in the current project. The FPDS project schedule has been updated to mesh with the current CEV development schedules and is also presented.

II. Current Status of Spacecraft Fire Safety Systems and Procedures Any discussion of fire prevention practices and/or detection and suppression systems for exploration systems

must begin by defining what is being or has been used on spacecraft. Of particular interest are areas where knowledge has been gained since the design of the systems on the ISS and STS Shuttle that could impact the design of next-generation systems. While the technologies to be developed in this plan are not intended for use on the ISS and STS, lessons learned from the fire detection and suppression system aboard these systems are relevant and will be identified.

1. Fire Prevention and Material Flammability

Existing material flammability acceptance test methods have been in place with little revision since the early days of manned spaceflight. The criteria applied in these acceptance tests were developed more from a phenomenological basis than the quantification of the risk of a fire. At this time, material flammability characterization used in support of selection or rejection of materials for use in spacecraft is based on NASA-STD-6001: Flammability, Odor, Offgassing, and Compatibility Requirements and Test Procedures for Materials in Environments that Support Combustion.2 The Upward Flame Propagation test (Test 1) is conducted in a normal gravity environment with the ambient conditions (gas composition and pressure) set equal to that of the worst-case environment to which the material will be exposed. As shown in Fig. 1, a vertical strip of material typically 5 cm wide, 33 cm long and of the worst-case thickness is ignited at the bottom and the flame spread up the strip is measured. A material fails Test 1 if it burns more than 15 cm or drips flaming debris on a piece of K-10 paper placed 20 cm below the sample. While this may represent a worst-case scenario on Earth, research conducted in microgravity has shown clearly that the ignition behavior and flame spread rate for any given material is quite different under low- and microgravity conditions at various imposed (ventilation) velocities (including zero cross-flow) than under the buoyancy-driven convection conditions naturally present in the upward spread tests.3-5 Accordingly, the results of the NASA-STD-6001 Test 1 do not map quantitatively to those in the low- or partial-gravity environment of an exploration vehicle or habitat. A second test (Test 2) uses a standard oxygen-consumption cone-calorimeter to provide quantitative data on ignition delay times and burning rates of materials. However, the parameters measured by this test are also dominated by buoyancy so their relationship to reduced gravity behavior is uncertain. 2. Fire Detection

In terms of fire detection, there is not consensus as to the best system as evidenced by the different systems used in the Russian and U.S. modules of the ISS and the STS. The STS and the Russian modules of the ISS use ionization-based smoke detectors while photoelectric smoke detectors are used on the U.S. modules. (A photograph of the STS smoke detector is shown in Fig. 2 while the ISS photoelectric detector is shown in Fig. 3) However, the

Figure 1. Experimental configuration for the Upward Flame Propagation test (Test 1). The specimen is 33 x 5 cm and the “worst-case” thickness. A chemical igniter is used if the O2 mole fraction is less than 50%. Otherwise, a silicone igniter is used.

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Comparative Soot Diagnostic (CSD) experiment, which flew in the Glovebox on STS-75, provided data concerning the performance of NASA’s smoke detectors in microgravity and provided particle size information for three types of solid smoke particulate. The most important finding of CSD was that for liquid smoke aerosols, the microgravity performance of the space shuttle (STS) smoke detector was substantially reduced from that in normal gravity.6 It was hypothesized that this performance difference was due to extended growth of the liquid smoke particulate in low-gravity due to the longer residence times in high smoke concentration regions. These findings have considerable implications for the design of smoke detectors for exploration vehicles but were unavailable when design studies were performed to select the smoke detectors on the STS or ISS.

3. Fire Suppression The STS currently uses a Halon-based suppressant with portable extinguishers available for crew use and a fixed delivery system within the avionics bays. The U.S. modules of the ISS utilize a gaseous CO2 suppressant delivered by portable extinguishers, shown in Fig. 4, while the Russian modules use portable water-based foam extinguishers. The U.S. CO2 extinguishers are charged with 2.7 kg of CO2 gas at a pressure of 5.9 MPa at 21 deg C. The design requirement is that when discharged, the CO2 could reduce the O2 concentration in an International Standard Payload Rack (ISRP) (approximately 0.73 m x 0.97m x 1.75m with a useable volume of 1.6 m3) by 50% within 60 sec. This is based on the NFPA 12 regulations that require a CO2 concentration of 50% be achievable when extinguishing smoldering fires and 34% for flaming combustion.7 (NFPA 12 also requires that the 50% concentration for smoldering fires be held for 20 minutes to ensure the fire is extinguished.) Little has been done to determine which of these approaches is most effective in suppressing a reduced-gravity fire and least invasive in terms of post-fire toxicology and cleanup. 4. Fire Response

Upon a verified fire alarm, the automated or manual crew response is to isolate the affected zone and to remove power and local or general air circulation. Donning a protective helmet (STS) or portable breathing apparatus (ISS) and dispensing the fire extinguisher are at the discretion of the crew depending on the severity of the event. These actions have been adequate to combat all U.S. potential fire situations and to date no fire extinguisher has been activated on either the STS or ISS.

Figure 2. Brunswick Defense™ smoke detector used in the NASA shuttle fleet. The inlet is on the right and the gas is expelled out the small plate on the top.

Figure 3. Allied Signal/Honeywell light-scattering smoke detector used in the ISS. The near IR laser beam emerges from the enclosure into the top assembly (A) and is reflected by two mirrors (one visible at top right (B)) and is then reflected back to the sensors in the enclosure (C). One sensor detects the forward scattered light and is referenced by another sensor that looks directly at the incident beam.

Figure 4. Portable CO2 fire extinguisher used on the U.S. modules of the ISS. The orange jacket provides thermal protection because the extinguisher gets cold during discharge. The straight nozzle is shown in the front pocket of the jacket.

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A critical part of this response strategy is the assumption that without forced ventilation, a microgravity fire will not propagate. Research has verified that in most microgravity fire situations, flames in a quiescent environment do self-extinguish. This behavior implies that a minimum atmospheric flow rate is necessary in low gravity to maintain fire propagation (and conversely to assure extinction). However, this limiting forced flow velocity can be on the order of only 0.5 cm/s as found by Ivanov et al.8 for polyethylene rods. These researchers also found that upon cessation of the airflow, flame extinguishment was not immediate and required up to 20 sec for the flame to be suppressed. Ensuring that the airflow velocity will be reduced below these levels in a cabin in which crew members are responding to a fire alarm will be difficult. Obviously, this strategy is inappropriate for operations on either the Moon or Mars where the 1/6 and 3/8-gravity levels, respectively, will induce a natural convective flow that draws oxygen into the flame. This will be exacerbated by the potentially higher oxygen mole fractions currently being considered for the Lunar Surface Access Module.

III. Assumptions The decision to accelerate CEV development from 2014 to 2011 identified in the previous section certainly

impacted how much new technology could be incorporated into the CEV. However, with this date set, the technology development efforts must then focus on when the technology is needed and what level of development is required by that date. This is discussed in the following section.

A. Development of the Crew Exploration Vehicle The Exploration Systems Architecture Study (ESAS) set the schedule for the development of the CEV and the

Lunar Surface Access Module (LSAM), the crewed vehicles that are the primary targets for the FPDS technologies. Of particular importance are the Preliminary Design Review (PDR) and the Critical Design Review (CDR). The Preliminary Design Review is conducted after the completion of the preliminary design synthesis and before the detailed design process. With respect to the infusion of new technology, one of the objectives of the PDR is to review the results of breadboard level testing directed at resolving feasibility issues. New technologies that require additional testing and maturation before use would each be examined carefully to ensure they are truly necessary. The Critical Design Review is conducted after the design has reached the degree of completion needed to permit a comprehensive and detailed examination, verification, and data analysis. The CDR is conducted after the review of engineering model system testing and prior to release of drawings for fabrication. With these definitions, new technology must be sufficiently matured by PDR to be included in the preliminary design. Any required development or testing must be identified and included in the schedule and budget to proceed to CDR.

Table 1 shows the estimated PDR and CDR dates for the CEV and LSAM. Of particular note is that in all cases, there is only approximately one year between PDR and CDR -- very little time for any technology that is “marginally-ready” to be prepared and incorporated into the final design. Also, there are only about four years between PDR and the earliest planned deployment of the vehicle which is very short by vehicle development standards.

B. Technology Readiness Levels NASA assesses the maturity of a technology on a scale of 1 through 9 relative to whether it is ready to be

implemented into a flight system. A brief definition of the Technology Readiness Level is given in Table 2. Typically, a technology must be at a Technology Readiness Level (TRL) of at least 6 to be incorporated into the design of a vehicle at the Preliminary Design Review. As noted in the table, TRL 6 implies that a system model or prototype has been demonstrated in a relevant environment. Because the behavior of fire in low- and partial-gravity is considerably different than in normal gravity, this implies ground-based or space-based low-g testing for new technologies in an overall fire protection strategy. This must be factored into all aspects of the FPDS project including, definition of deliverables, implementation, schedule, and budget.

C. Initial Conditions and Implications The implications of three events permeate throughout the work accomplished in FPDS over past year and the

plans that have been made for future years. First, the Exploration Systems Architecture Study released in September

Table 1. CEV Development Schedule

Block Definition PDR CDR1A CEV: ISS 3Q 2007 4Q 20082 CEV: Lunar 3Q 2008 4Q 2009

Lunar Surface Access Module 1Q 2013 1Q 2014Source: www.nasawatch.com (3 Jan 2006); NASA's Exploration System Architecture Study, NASA-TM-2005-214062, November 2005

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Table 2. Technology Readiness Level Definitions

TRL Definition1 Basic principles observed and reported 2 Technology concept and/or application formulated

3 Analytical and experimental critical function and/or characteristic proof-of-concept

4 Component and/or breadboard validation in laboratory environment

5 Component and/or breadboard validation in relevant environment

6 System/subsystem model or prototype demonstration in a relevant environment (ground or space)

7 System prototype demonstration in a space environment

8 Actual system completed and "flight qualified" through test and demonstration (ground or space)

9 Actual system "flight proven" through successful mission operations

2005 changed the need for technology development, at least for the near-term implementation of the Vision for Space Exploration. This impacted the budget allocated to the FPDS work and several specific work items will be identified in the following section. Second, because of the changes in budget allocations resulting from the ESAS recommendations, the costs for ground-based microgravity facilities such as the 2.2-sec drop tower and the Zero-Gravity Facility must be borne completely by the projects that require them; the FPDS project in this case. The real issue is that these costs are not only incurred when the facility is in use but continuously in order to keep the facility operational. The third event that significantly impacts the FPDS program is that the re-structuring of NASA to implement the Vision has decreased the focus on peer-reviewed basic research funded through NASA Research Announcements. To provide a more gentle termination of this work, projects will be funded through FY06 but will then cease at the beginning of FY07, even for projects that would have been funded through FY08. Unfortunately, the current FPDS budget does not permit some of the projects that were relevant to the exploration initiative to be funded beyond FY06. The impact of the premature termination of this work will be discussed in the following sections.

IV. FPDS Deliverables When incorporated into the design philosophy and functional design of exploration vehicles and habitats, the

deliverables of the FPDS project will quantitatively reduce the likelihood of a fire and reduce the extent and degree of equipment damage should a fire occur. These deliverables (or products) have been developed through a series of workshops that focused on spacecraft fire safety9-11 as well as previous studies and reports that have addressed fire protection in spacecraft.12-14 The most recent workshops were held in 2001,9 2003,10 and 2004; the first workshop was held in 1986.11 At each of these workshops, input was obtained from designers and operators of the STS and ISS and was used to formulate the products required for exploration systems. As requirements for the CEV and LSAM have become better defined over the last year, this information has been incorporated into the FPDS research plans. For the most part, this input has impacted conditions to be evaluated or research priorities rather than adding or removing a deliverable.

In spite of the change in NASA’s implementation of the Vision for Space Exploration over the last year (and the associated change in budget), the deliverables of the Fire Prevention, Detection, and Suppression project have remained essentially the same as that outlined by Ruff et al.1 in 2005. What has changed, however, is how these components are implemented and the fraction of the overall effort devoted to each. The deliverables of the FPDS projects are as follows:

Fire Prevention and Material Flammability 1. Normal gravity material flammability test to evaluate reduced gravity flammability 2. Material flammability assessment in candidate atmospheres for exploration transit vehicles and habitats 3. Definition of realistic fire scenarios for exploration spacecraft and habitats Fire Signatures and Detection 4 Advanced detection system for gaseous and particulate pre-fire and fire signatures 5. Verified models of the transport of contaminants, smoke, and combustion gases throughout the habitable volume of a spacecraft or habitat Fire Suppression and Response 6 Design rules for suppressant system including effectiveness of suppressants, required concentrations, and dispersion methods 7. Simulations of fire and fire-response scenarios for system evaluation and crew training

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A more detailed description of these deliverables and the accomplishments made towards achieving each is

discussed in the following section.

V. Description and Status The success of the FPDS project hinges on delivering the products identified in the previous section to the

Exploration Systems Mission Directorate. In spite of the uncertainty in NASA’s organization and implementation of the VSE over the past year, progress has been made toward each of these deliverables. In this section, a short description of each deliverable is given along with a discussion of the accomplishments, future plans, and challenges facing each of them.

A. Fire Prevention and Material Flammability 1. Normal gravity material flammability test to evaluate reduced gravity flammability

Existing material flammability acceptance test methods have been in place with little revision since the early days of manned spaceflight. The criteria applied in these acceptance tests were developed more from a phenomenological basis than quantification of the risk of a fire. Microgravity testing has identified that some materials become more flammable (as evidenced by a lower limiting oxygen index) in a reduced gravity convective flow than under normal gravity conditions3 indicating that the current test may not be conservative in all cases, although the actual margin of safety is unknown. The deliverable from this effort will be a standardized test (or tests) that can be conducted in normal gravity to accurately assess material flammability in low and partial gravity levels.

Status

Prior to this year, one of the primary tasks toward achieving this goal was to develop and implement an experiment in the FEANICS (Flow Enclosure Accommodating Novel Investigations in Combustion of Solids) insert to the Combustion Integrated Rack on the ISS. The objective of this experiment was to obtain long-duration flammability data that would be used to verify the normal gravity test to evaluate reduced gravity flammability. This test could be either in the configuration of the Forced Ignition and Spread Test15 (FIST) planned for CIR or, by analogy, other normal gravity tests being developed in the FPDS program. However, the funding for the FEANICS insert was cut as a result of the Exploration Systems Architecture Study making the verification of any new ground test method more difficult because it must be accomplished without a flight verification test. To address this, researchers are continuing to develop the ground-based FIST apparatus as well as investigate several test techniques that make use of configurations that suppress the effect of buoyancy. In one of these methods, buoyancy is suppressed by burning a sample between two plates separated a distance less than the critical Rayleigh number.16 A second test is similar to a cone calorimeter test except that the sample is burned above the radiant heater in a ceiling configuration.17 In this configuration, the velocity gradient normal to the flame sheet is largely determined by the velocity of the incoming flow rather than buoyancy. Currently without the prospects of a flight verification test, these efforts are focusing on flammability measurements that can be verified using a combination of testing in ground-based microgravity facilities and detailed computational and analytical models.

The second avenue of research is to better understand the flammability test NASA currently uses to screen materials for use in spacecraft (NASA-STD-6001 Test 1). Specifically, this work is evaluating upward flame spread to attempt to translate the result from normal-gravity to microgravity.18 Feier et al.19 are also investigating how to use scale results from upward flame spread experiments conducted at reduced pressures to simulate upward flame spread rates in partial gravity. This work is continuing to establish the limitations of this scaling, the functional relationship for sample width, and the effect of observed unsteady growing modes for upward flame spread.

2. Material flammability assessment in candidate atmospheres for exploration transit vehicles and habitats

As the CEV and LSAM architecture has become more developed, the need to define the composition of the atmosphere and ambient pressure for the habitable volume has received more attention. The atmosphere of previous spacecraft has ranged from 100% O2, 34.5 kPa for Mercury, Gemini, and Apollo missions to standard air (21% O2/79% N2, 1 atm) for ISS and STS. (Atmospheric conditions prior to EVA are different from the standard cabin atmosphere.) These design points are shown in Fig. 5 and generally lie along the normoxic equivalent line, i.e., having the same O2 partial pressure as 100 kPa, 21% O2 by volume.20 In order to maintain O2 partial pressure along the normoxic line, the %O2 increases as the total pressure decreases. Yet, it is the mole fraction of oxygen that affects the flammability of materials. The increased material flammability of these conditions is critical in terms of fire initiation, propagation, and suppression.

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As evidenced by the range of atmospheres that have been used, there is no optimum atmosphere for space vehicles; each application requires a detailed evaluation of the mission objectives and constraints. Various trade studies have indicated significant advantages associated with operation at total pressures considerably lower than one atmosphere.20 Status

Following the study by Lange et al.,20 the Exploration Systems Mission Directorate (ESMD), as part of the NASA inter-organizational Human System Working Group (HSWG), chartered the Exploration Atmospheres Working Group (EAWG) and tasked it to generate recommendations on the characteristics of internal atmospheres for exploration spacecraft, including space suits and planetary exploration vehicles. The EAWG consisted of experts in space medicine and physiology, mission operations, and vehicle and habitat systems, including those concerned with the flammability of materials. At the EAWG workshop held in November 2005, the region shown by the box in Fig. 5 was found to be a suitable compromise for the LSAM cabin atmosphere. (The EAWG final report is being prepared and will provide detailed assumptions and recommendations.)

One of the major questions that arose during the deliberations of the working group was “What is the quantitative effect of elevated mole fractions of oxygen and reduced ambient pressure on material flammability in low- and partial-gravity?” While NASA’s Microgravity Combustion Science Program has greatly increased our understanding of combustion in microgravity, data is limited at the conditions of primary interest for atmosphere selection. For example, McAlevy and Magee21 produced correlations of downward flame spread rate but these were in normal gravity and required extrapolation to reach the desired conditions. Frey and T’ien,22 Neustein et al.23 and Huggett et al.24 all produced correlations of flame spread rate at relevant pressures and O2 mole fractions in various configurations but in normal gravity. Son et al.25 have evaluated flame spread over open cell polyurethane foam using various gas mixtures, pressures, and O2 concentrations in normal and microgravity. These results showed a significant effect of gravity but there was no imposed flow and the test conditions were not specifically at conditions being considered for cabin atmospheres.

To obtain microgravity data to assess material flammability in candidate atmospheres, an existing facility is being upgraded to allow testing at oxygen concentrations up to 50%. These tests will be conducted in the Zero-Gravity Facility at NASA GRC and result in a quantitative assessment of the effect of high O2 mole fractions at lower ambient pressures on the flammability of a set of typical spacecraft materials. These tests will begin later in 2006. Several of the computational models that have been developed in past microgravity combustion research will also be used to evaluate these conditions.

3. Definition of realistic fire scenarios for exploration spacecraft and habitats

The science of fire protection engineering in terrestrial applications has developed considerably since the specifications were written for either the STS or ISS. Not only do we better understand the mechanisms of ignition, flame spread and fire growth, we now possess better computational models that can be used to predict the development and outcomes of the fires. These tools have been developed to evaluate terrestrial fire safety issues such as the suitability of material flammability criteria, the design of fire detection and suppression systems, and the adequacy of fire response strategies to provide a quantifiable level of fire protection. Even though an equivalent evaluation and assessment is desired by designers of exploration spacecraft and habitats, these tools have generally not been applied in a systematic way to analyze fire scenarios in microgravity and partial gravity environments. Granted, development of these tools for terrestrial fire safety applications have the huge advantage of being able to

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Figure 5. Design space for cabin atmosphere and pressure and O2 concentration. Arrows indicate the trends for increasing risk of decompression sickness as a result of EVA, hypoxia, and flammability.20

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conduct extensive testing using relevant materials and full-sized configurations. However, when coupled with the existing knowledge of flame spread and fire development in reduced gravity, these tools can be tailored to evaluate various fire scenarios relevant for exploration spacecraft and habitats and yield practical information upon which design and operational decisions can be based. At the very least, it would provide a rational methodology to assess what information is known about fires in reduced gravity and what data is required to adequately define a fire scenario.

Status

Most of the work in this area is being conducted by grants to external researchers selected in previous Microgravity Combustion Science NRAs. A workshop was held in April 2005 at NASA GRC to assess this work and direct these researchers toward the development of the tools discussed above. While this work is progressing, these grants will prematurely end in September 2006. We are currently assessing how to get the most out of these efforts before that time and then continue open work into FY07.

B. Fire Signatures and Detection 4. Advanced detection system for gaseous and particulate pre-fire and fire signatures

Smoke detectors on the ISS have proven to be sensitive to dust and have produced numerous false alarms. As such, there is an immediate need for new fire detector technology that eliminates nuisance alarms. This problem will only be exacerbated on long-duration exploration missions in both transit vehicles and surface habitats. The spacecraft fire detection system developed in this work should be able to (1) detect a fire with minimal false or nuisance alarms, (2) minimize the time from the beginning of a pyrolysis or pre-fire event to the time an alarm sounds, (3) indicate to the crew the location of the fire, and (4) identify the source of the fire from the measured signature. Status

The tasks required to accomplish this goal include sensor development and verification, development of the logic to allow a distributed network of sensors to assist in locating and assessing a fire, and quantification of fire and pre-fire signatures in reduced gravity. Together with the FAA, the FPDS program has funded the development of a suite of particulate and gas sensors that have demonstrated excellent rejection of false positives while maintaining sensitivity to actual fires. While developing sensors, it is also important to evaluate their performance using relevant samples and a consistent methodology. The suite of these gas and particulate sensors were evaluated using samples of cotton, silicon rubber, Teflon™, and Kapton™ in December 2004. In March 2005, similar tests were conducted using an electronic nose developed by JPL, a potential technology for environmental monitoring. Additional evaluations of suites of these sensors are planned for early 2006. A facility to conduct similar tests in the C-9 Reduced Gravity Aircraft is also being prepared. We have begun to work with personnel responsible for the CEV Environmental Control and Life Support (ECLS) to develop requirements for the fire detection system and ensure the transfer of this technology and expertise to the prime contractors when selected.

The second part of this deliverable is to quantify the signatures of fire and pre-fire events in low-gravity so that the sensors can be tuned to respond to the proper concentrations of gases and sizes of particulates. The objective of the Smoke Aerosol Measurement Experiment (SAME) (PI: Dr. David L. Urban, NASA-GRC) is to conduct a test in the ISS Microgravity Science Glovebox to provide in situ particle size information for several smoke aerosols (solid and liquid).6 This data will further quantify the differences in the particle size and quantify the particulate pre-fire signatures of relevant spacecraft materials (Kapton™ and Teflon™, for example) and used to guide the development of optimized smoke detectors. The development of this experiment continued this year with several major events taking place. First, the Exploration Investigation Requirements Review (EIRR) was held in January 2005 in which the objectives and methodology of this experiment were evaluated both on the scientific merits of the project as well as the relevance to the development of advanced fire detectors. The panel was enthusiastic regarding the merits of the investigation and felt it would provide the information necessary to improve the reliability of spacecraft incipient fire detection systems. The SAME experiment is currently scheduled for Flight Hardware Availability in August of 2006 and launch aboard 13A.1 in March 2007. Second, the first two portions of the Dust Aerosol Measurement Feasibility Test (DAFT) were conducted on the ISS in February and March of 2005. This is a risk mitigation experiment for two diagnostics to be used by SAME to characterize the particle size. The two instruments, the P-Trak and the DustTrak, both functioned properly in that they each turned on, responded to manual control by the crew member and displayed particle counts and mass concentration readings. These results along with additional information on the SAME are documented in a recent paper by Urban et al.6 Additional tests are planned using calibrated aerosol sources and are currently awaiting a launch opportunity.

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Additional ground-based evaluation of gaseous fire signatures from various materials in normal gravity has been conducted this year (PI: Dr. L. VanderWal, NCMR). The objective of this work is to quantify the normal gravity signatures and determine if their time history are changed in reduced gravity. An added advantage of this project is that the facility is ideally suited to evaluate prototype fire detectors under development in this project. 5. Verified models of the transport of contaminants, smoke, and combustion gases throughout the habitable volume of a spacecraft or habitat

The effectiveness of even the most refined and exotic sensor will be reduced unless it is located in the right place and the time required for the contaminant to reach a detectable level at that location is known. The deliverable in this task is a validated computer model for the large-scale transport of smoke and combustion products within a habitable volume that can be used to evaluate fire detector location and activation.

Status

Because of the similarity between this work and the simulation of fire scenarios previously discussed, (Deliverable 3), there is no work devoted exclusively to this task. The tools that are developed for the evaluation of fire scenarios are adequate to perform these evaluations. As the CEV design matures and issues of air circulation and placement of fire detectors become more critical, these simulations will be initiated.

C. Fire Suppression and Response 6. Design rules for suppressant system including effectiveness of suppressants, required concentrations,

and dispersion methods Carbon dioxide was selected as the fire suppressant on the ISS primarily because of its use in terrestrial

applications. Fortunately, none of these extinguishers have been needed to extinguish a fire on a U.S. spacecraft. As a result, our knowledge of their effectiveness, the fire protection they actually supply, and the likely environmental conditions after they are deployed are unknown. The objective of this work is to develop rational data and guidelines for the design of fire suppression systems in microgravity as well as at Lunar and Martian partial gravity levels.

Status

The definition of the Flame Extinguishment Experiment (FLEX) to be conducted in the Multi-User Droplet Combustion Apparatus (MDCA) in the Combustion Integrated Rack (CIR) continued this year since both the CIR and MDCA remained generally intact at the completion of the architecture study. The objective of the FLEX experiment is to evaluate the effectiveness of various fire suppressants to extinguish a flame on a droplet configuration at ambient pressures and oxygen concentrations relevant for exploration vehicles and habitats. The critical Damköhler number will be extracted from the flame properties and droplet diameter at the time of extinction and used to relate data between the droplet and other configurations. The Limiting Oxygen Index (LOI) will also be measured as a function of pressure and oxygen concentration to determine the lowest O2 concentration that will sustain a low-gravity flame. Additionally, detailed simulations of the combustion process will be used to produce simplified models of combustion kinetics that can be used in the large-scale simulations of fire scenarios previously discussed (Deliverable 3). In November 2005, the Exploration Investigation Requirements Review was held at NASA GRC during which both the applicability of the experiment to spacecraft fire safety as well as the underlying science concepts were assessed. The review panel found the experiment would significantly enhance our understanding of fire suppression in reduced gravity and recommended that it proceed. The MDCA and CIR hardware successfully completed the Phase III Safety Review and the engineering Pre-Ship Review. It is currently on schedule to launch to the ISS on ULF-2 in May 2007.

Since the initial statement of the VSE in January 2004, plans have been made to include in the FEANICS insert the capability to evaluate fire suppression over combusting solid fuels. This data was being planned to provide a verification of the FLEX results and a more complete test of potential microgravity fire suppression strategies. However, the development of these tests ceased when the funding for the FEANICS insert was terminated.

Most of the other work in fire suppression is being conducted either at GRC or by external grants funded through previous Microgravity Combustion Science NRAs. Recently, this has included projects investigating fire suppression using opposed-flow diffusion flames,26 cup burners,27,28 and PMMA cylinders.29 However, these projects have either already ended or will end in FY06. As these projects end, we will gather and assess their outcomes, extract the portions that are most relevant to fire suppression in microgravity, incorporate results from previous studies, and draft an initial set of design rules and requirements. This synthesis of these results will be documented and used not only in trade studies of fire suppressants for CEV and LSAM but also to indicate specific knowledge gaps that must be filled by additional testing, analysis, or modeling.

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7. Simulations of fire and fire-response scenarios for system evaluation and crew training

Effective fire detection systems and suppression techniques are only as good as the training the crew receives to use them. Efficient use of the learned skills and the tools provided under what most likely will be a very tense and confusing situation is required to minimize equipment damage and limit the contamination of the cabin atmosphere either by combustion products or the fire extinguishing agent. Performing such a simulation in a physical cabin mock-up on Earth is pointless because the fire and fluid transport will be dominated by buoyancy and will behave very differently than in a reduced-gravity environment. The objective of this deliverable is to provide a virtual reality (VR) simulation in which the crew can experience a realistic fire scenario during ground-based training. Additionally, a VR simulation could be used to evaluate fire response scenarios to evaluate crew response relative to their capabilities and task demands.

Status

The two tasks required to accomplish this work are (1) simulations of a fire scenario including smoke transport and (2) advanced visualization tools to interpret the output from the simulations and translate the data into realistic images on either a computer screen or a virtual reality display. The work on the first task is basically the same as required for Deliverables 3 and 5. The work on the visualization aspects of this deliverable were started this past year and progress was made on creating realistic-looking smoke in a virtual environment using output of the simulations. However, this work was halted in FY05 because of funding constraints. There are advantages to working both the simulation and visualization issues simultaneously but this is not currently possible. We intend to resume this work as the simulations become sufficiently advanced and the requirements placed on the simulations for evaluation and realistic training can be better defined.

VI. Program Status and Schedule At this time, we have approximately 24 peer-reviewed tasks (extramural and intramural) directed toward fire

safety on exploration vehicles and habitats. As discussed in Section III.C., most of these will only be funded through the end of FY06 so we are working to complete the most critical portions of the work between now and then. Researchers at NASA GRC continue to work on the tasks identified in this paper. The Exploration Technology Development Office has been established at NASA Langley and requested that all projects prepare detailed project plans. A draft of the FPDS plan has been submitted for review and will be completed in January 2006.

The schedule of deliverables presented in the FPDS project plan is shown in Table 3. Comparing these dates with those shown in Table 1, the material flammability deliverables will not be completed in time for the PDR of the Block 1 CEV. However, the atmospheric conditions of this vehicle will most likely be similar to those used in STS and ISS. However, material flammability issues arise throughout the vehicle lifetime so the test techniques and resulting data will be useful for CEV even if obtained after the CDR. Assuming that the Block 2 CEV will have an atmosphere similar to Block 1, the material flammability deliverables will be most necessary for the PDR of the LSAM in which the highest oxygen concentrations will most likely be used. The development of advanced fire detectors and fire suppression technologies are most linked to the PDR for both the CEV and LSAM. It will be critical to proceed with these efforts as rapidly as possible and work closely with personnel involved with CEV development to ensure that the technological developments are disseminated as rapidly as possible. The fire signature milestones (SAME flight experiment and the ground-based testing) are related more to detection limits which could be determined after prototypes of the flight hardware are built and tested. The CEV PDR and, hence, the concept for the fire suppression system, will be completed before the FLEX flight experiment. Therefore, data for CEV trade studies must come

Table 3. Milestone schedule for FPDS products Date

Fire Prevention and Material FlammabilityAssessment of reduced gravity flammability in relevant atmospheres 2Q FY07Definition of normal gravity tests for select reduced-gravity flammability parameters 4Q FY07Verification of normal gravity flammability tests (analysis and/or experiments) 4Q FY08

Fire Signatures and Detection

Reduced gravity tests of suite of gas and particulate sensors 3Q FY06Database of fire and pre-fire signature in microgravity 2Q FY07Quantification of the size distribution of pre-fire pyrolysis particulate (SAME) 3Q FY07Advanced fire detector suite 3Q FY07Verified models of smoke and contaminant transport in microgravity 3Q FY08

Fire Suppression and ResponseQuantification of suppressant effectiveness in microgravity (FLEX) 4Q FY07Design rules for suppressant system design and operation 3Q FY08

Deliverable

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from current and past work in microgravity fire suppression. The FLEX results should be obtained in time for the LSAM PDR.

VII. Conclusion This paper identified the deliverables for the FPDS project and provided a brief status report on major work

items. The seven primary deliverables are in the form of hardware, software, and/or information (e.g., data libraries) and a tentative schedule for their completion is shown relative to the current CEV and LSAM development schedules. Throughout this paper, the impact of the outcomes of the Exploration Systems Architecture Study on all of the efforts within FPDS was identified. Obviously, the effect of this study on FPDS has been extensive as it has for most of NASA’s advanced technology development efforts. However, fire safety on exploration spacecraft is important for the success of the mission and the successful implementation of the Vision for Space Exploration and will play a role in vehicle design and operation. This project provides NASA’s primary expertise in reduced gravity fire behavior as well as fire detection and suppression. As such, it plays a very important role in the implementation of the Vision for Space Exploration. The most critical aspects of this project are to (1) continue to make progress on all of the deliverables so that they reach TRL 6 by the appropriate need date (typically PDR), (2) be responsive to the NASA and contractor CEV development team as their designs progress and (3) participate in NASA-wide working groups and standard development activities to have input to the design and operational requirements for exploration habitats and vehicles.

Currently, we are focused on implementing the research indicated in this paper in the discussion of the status of the FPDS deliverables. With the budget reductions, the number of NASA and external researchers has certainly declined. However, the remaining FPDS work is important to the exploration mission and we will continue to strive toward the objective of ensuring crew health and safety on exploration missions by reducing the risk of fire and giving the crew the proper tools and knowledge that would allow them to continue the mission should a fire occur.

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