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Saffire (Spacecraft Fire Experiment)

Overview     Launch    References

 

Saffire is a NASA space flight experiment that will increase understanding of how an accidental fire might behave in a spacecraft after it leaves Earth's atmosphere. The first of three planned flight experiments is scheduled on the return flight of the Orbital ATK Cygnus CRS OA-6 cargo vehicle from the ISS into the Pacific Ocean.

Understanding how fire spreads in a microgravity environment is critical to the safety of astronauts who live and work in space. And while NASA has conducted studies aboard the space shuttle and International Space Station, risks to the crew have forced these experiments to be limited in size and scope. 1) 2) 3) 4) 5)

Now a new experiment, designed, built and managed at NASA(GRC (Glenn Research Center), will ignite an understanding of microgravity fire on a much larger scale. Saffire is a series of experiments to be launched on three different flights beginning in March 2016.

Saffire will involve far larger flames than previous experiments and will investigate the way fire spreads on a variety of combustible materials. Because the experiments will be conducted away from the space station, there is no risk to the astronauts aboard.

Each Saffire experiment will be remotely operated inside a module of ~1 m x 1.5 m, split into two compartments. One side of the module is an avionics bay that contains sensors, high definition video cameras and signal processing equipment. The other side contains the hardware required to ignite a large flame and burn the fabrics and materials inside (Figure 1).

When the experiments begin, Saffire-I (on CRS-6) and -III will burn one large 40 cm x 100 cm piece of SIBAL (Solid Inflammability Boundary at Low Speed) cloth, which is a blend of fiberglass and cotton. This material has been studied in previous microgravity combustion experiments, although at a much smaller size. The SIBAL cloth will be burned from the bottom to see how the flame spreads. If the flame extinguishes itself, scientists will light it at the top and see what happens as the flame moves opposite to the airflow.

The Saffire I experiment will be started within the first day of the Cygnus return flight which will run autonomously once the command is sent. It will only take a few hours to run the experiments, but Cygnus will remain in space for seven days to ensure complete data transmission back to the Saffire operations team on the ground.

Cygnus burns up on reentry into the Earth's atmosphere. Consequently, the flight unit is permanently disposed of during this process. No specific disposal processes are expected if the experiment hardware is burned up upon re-entry.

The Saffire-I experiment provides a new way to study a realistic fire on an exploration vehicle, which has not been possible in the past because the risks are too high. Instruments on an unmanned cargo vessel measure oxygen, carbon dioxide, heat, pressure and flame growth, and two video cameras provide views of the flame. Results determine microgravity flammability limits for several spacecraft materials, help to validate NASA's material selection criteria, and how microgravity and limited oxygen affect flame size. The investigation is crucial for the safety of current and future space missions.

 

Once the capsule undocks in May 2016 from the ISS on its return flight and is far away from the space station, ground control will trigger the fire on board. The results of this Saffire-1 experiment will determine how much fire resistance is needed in the ultra-light material used in the spacecraft and the astronaut's gear. It will also help NASA build better fire detection and suppression systems for their spaceships, and study how microgravity and limited amounts of oxygen affect the size of the flames.

Working with a team of researchers from 11 U.S. and international government agencies and universities, NASA's Saffire-1 experiment will be remotely conducted by Saffire and Orbital ATK personnel from the Orbital ATK Control Center in Dulles, Va. 6)

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Figure 1: Schematic of the Saffire Experiment Module (top cover removed for clarity). The hardware consists of a flow duct containing the sample card and an avionics bay. All power, computer, and data acquisition modules are contained in the bay. Dimensions are approximately 53 x 90 x 133 cm (image credit: NASA)

 

Background: The NASA Advanced Exploration Systems program funded a project to develop and demonstrate spacecraft fire safety technologies in relevant environments. The keystone of these demonstrations is a large-scale fire safety experiment conducted on an ISS resupply vehicle after it has undocked from the ISS and before it enters the atmosphere. The project team from NASA/GRC is augmented by an international topical team assembled by ESA (European Space Agency). Each member of this team brings expertise and funding from their respective space and research agencies for their activities. This participation of members from other countries and space agencies not only brings additional skills to the science team, but also facilitates international cooperation in the development of an approach to spacecraft fire prevention and response for future exploration vehicles. 7)

No single experiment can address the range of issues that need to be resolved to fully understand the spacecraft fire risk and to ensure the safety of future flights. The goal of the topical team is to leverage the international capabilities of the team to develop a suite of ground-based and space flight spacecraft fire safety experiments to expand the impact of the flight experiments. The current experiment has been designed to address two objectives. The first objective is to understand the flame spread and growth of a fire over an amount of flammable material consistent with what is likely to be in a spacecraft cabin through the development of an experiment for a sample material approximately 1 m long. This is at least an order of magnitude larger than any prior low-g flame spread experiment. The second objective is to examine the flammability limits of materials in low gravity to determine if NASA's material selection methods are a reasonable predictor of low-gravity flammability.

The unique objectives of Spacecraft Fire Experiment-I (Saffire-I) necessitated the use of an ISS expendable resupply vehicle such as ESA's ATV, JAXA's HTV, or Orbital Sciences Corporation's (Orbital's) Cygnus vehicles. Early in the development of the project, the ESA became interested in this experiment. As a result, the ATV was the initial vehicle for which an experiment concept was developed. While many factors could go into the selection of a vehicle such as available volume, power availability, communication, etc., the schedule and resources eventually become the most significant. With the planned ATV flights ending with ATV-5, it became unlikely that an experiment could be developed and integrated with the vehicle within that schedule. Since Orbital's eight Cygnus flights were planned to begin in 2013 and extend through 2016, Cygnus was a more promising vehicle for the successful completion of this experiment. Programmatic requirements drives the project to plan for three experiments to be performed on three consecutive flights of Cygnus. The first experiment would take place on the 5th Cygnus flight.

The concept for this experiment focuses on conducting two types of material combustion tests that are performed on different flights using the flow duct design. The experiment package consists of a flow duct and an adjacent avionics bay. The avionics bay is connected to the side of the flow duct. The top and bottom structures on the experiment module are the fan unit on the top and the flow straightener unit on the bottom. The airflow is from the bottom to the top of the experiment module. The flow duct/avionics bay assembly is a rigid structure and will be secured with the standard stowage straps. This duct enables a more uniform flow across the samples, maintain a clear flow path within the experiment module, and prevent burning debris from interacting with the rest of the cargo.

The experiment package has a range of diagnostics to monitor the test conditions. The ambient temperature and the oxygen and CO2 concentrations are measured at the intake of the flow duct with temperature measurements also made just upstream of the fans. A pressure transducer also delivers the pressure time-history. Flow anemometers are placed at selected locations in the inlet flow and thereby quantify the oxidizer flux in the duct. Two video cameras provide top views of the entire sample. The sample is periodically illuminated by a LED source to allow the measurement of the pyrolysis length.

For the flame spread sample, the flame stand-off distance is measured using several thermocouples placed at varying heights above the sample surface. These are woven into the sample and then bent so they are perpendicular to the surface. Finally, a calibrated radiometer measures the broadband radiative emission from the sample to provide an estimate of the radiative flux from the burning zone towards the surroundings.

The first and third tests (Saffire-I and -III) investigate flame spread and growth in low-gravity to determine if there is a limiting flame size and to quantify the size and growth rate of flames over large surfaces. The flame propagates over a panel of thin material approximately 0.4 m wide by 1.0 m long. The ignition method is a hot wire along the upstream edge. This material is expected to burn at the anticipated cabin atmosphere. The objective of this test is to quantify the flame development over a large sample in low-gravity. The objective of the second set of tests (Saffire-II) is to investigate the low-gravity MOC (Maximum Oxygen Concentration) flammability limits in long-term low gravity. The configuration for these experiments consists of nine samples of varying materials (denoted flammability samples) each having dimensions of approximately 5 cm wide by 30 cm long installed on the same panel in place of the single sample. These samples emulate the configuration used in NASA-STD-6001 Test 1. Each sample is ignited at the bottom using a hot wire. The oxygen concentration in the vehicle is expected to be nearly 21% by volume—the same as in the ISS when the hatch is closed. The materials would be selected to be near their normal-gravity or hypothesized low-gravity maximum oxygen concentration in 21% O2. This complicates the selection of sample materials because most materials relevant for spacecraft do not have normal-gravity flammability limits near 21% oxygen by volume. Camera images would be the primary diagnostics for these tests as the intended result is primarily to determine whether the flame propagates or self-extinguishes.

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Figure 2: Saffire experiment module with foam packing and straps as it will be mounted in Cygnus (image credit: NASA)

 

Launch: The Saffire experiment module, as part of the Cygnus CRS OA-6 cargo of the commercial OA (Orbital ATK) mission to the ISS, was launched on March 23, 2016 (03:05:51UTC) atop a ULA (United Launch Alliance) Atlas-5 vehicle. The launch site was Cape Canaveral SLC-41 (Satellite Launch Complex-41). This was the second flight of an enhanced Cygnus spacecraft to the ISS and the fifth of ten flights by Orbital ATK under the Commercial Resupply Services contract with NASA. 8) 9)

Cygnus spacecraft are named after former astronauts. OA-6 is named the SS Rick Husband, after the commander of Space Shuttle Columbia's ill-fated STS-107 mission. Husband was killed on February 1, 2003 when the Columbia space shuttle disintegrated as she reentered Earth's atmosphere at the end of a two-week microgravity research mission. None of the seven astronauts aboard survived.

Orbit: The near-circular orbit of the ISS is at a nominal altitude of ~400 km with an inclination of 51.6º.

Cygnus carried a payload of 3513 kg of science and research, crew supplies and vehicle hardware to the orbital laboratory to support dozens of science and research investigations that will occur during Expeditions 47 and 48. 10)

The Cygnus spacecraft will arrive at the station on March 26, at which time Expedition 47 Commander Tim Kopra of NASA and Flight Engineer Tim Peake of ESA (European Space Agency) will grapple Cygnus, using the space station's robotic arm. After Cygnus capture, ground commands will be sent from mission control in Houston to the station's arm to rotate and install the spacecraft on the bottom of the station's Unity module. The Cygnus vehicle will remain at the space station until May, when the spacecraft will be used to dispose of several tons of trash during its fiery reentry into Earth's atmosphere.

The Saffire module remains aboard the Cygnus vehicle while supplies for the station are offloaded. The experiment is conducted during the return trip to Earth.

A few of the scientific highlights: 11) 12)

• Gecko Gripper, testing a mechanism similar to the tiny hairs on geckos' feet that lets them stick to surfaces using an adhesive that doesn't wear off.

• Meteor, an instrument to evaluate from space the chemical composition of meteors entering Earth's atmosphere. The instrument is being re-flown following its loss on earlier supply missions.

• Saffire, which will set a large fire inside the Cygnus in an unprecedented study to see how large fires behave in space. The research is vital to selecting systems and designing procedures future crews of long-duration missions can use for fighting fires.

• Strata-1 to study regolith behavior in microgravity (to investigate how easy or difficult it is to anchor a spacecraft in regolith). The Strata-1 experimental facility exposes a series of regolith simulants, including pulverized meteorite material, glass beads, and regolith simulants composed of terrestrial materials and stored in multiple transparent tubes, to prolonged microgravity on the space station.

• AMF (Additive Manufacturing Facility) of Made In Space Inc. of Mountain View, CA will be installed as a permanent AM (Additive Manufacturing) 3D printing device in an Express Rack. The AMF uses this technology to enable the production of components on the space station for both NASA and commercial objectives.

• In addition, Cygnus is carrying more than two dozen CubeSats/nanosatellites that will be ejected from either the spacecraft or the station at various times during the mission to evaluate a range of technology and science topics including Earth observations.

• Diwata-1 is a microsatellite (50 kg) of the University of the Philippines.

 


1) Nancy Smith Kilkenny, "Fire in the Hole: Studying How Flames Grow in Space," NASA, March 3, 2016, URL: https://www.nasa.gov/feature/fire-in-the-hole-studying-how-flames-grow-in-space

2) Frank Jennings, Jr. Jan Wittry, "NASA Pursues Burning Desire to Study Fire Safety in Space," NASA, News Release 16-006, March 16, 2016, URL: https://www.nasa.gov/press-release/nasa-pursues-burning-desire-to-study-fire-safety-in-space

3) Gary A. Ruff, David L. Urban, A. Carlos Fernandez-Pello, James S. T'ien, Jose L. Torero, Guillaume Legros, Christian Eigenbrod, Nickolay Smirnow, Osamu Fujita, Adam J. Cowlard, Sebastian Rouvreau, Oliver Minster, Grunde Jomass, "Spacecraft Fire Experiment (Saffire) Development Status," Proceedings of the 44th International Conference on Environmental Systems (ICES), Tucson, AZ, USA, July 13-17, 2014, URL: http://orbit.dtu.dk/ws/files/97737980/2014_ICES_SFS_Demo_Paper_265_5_16_2014.pdf

4) Justin E. Niehaus, Paul V. Ferkul, Suleyman A. Gokoglu, Gary A. Ruff, "Buoyant Effects on the Flammability of Silicone Samples Planned for the Spacecraft Fire Experiment (Saffire)," 45 th International Conference on Environmental Systems (ICES), Bellevue, WA, USA, July 12-16, 2015, URL: http://tinyurl.com/jebe3mq

5) David L. Urban, Gary A. Ruff, Olivier Minster, A. Fernandez Pello, James T`ien, Jose Torero, Guillaume Legros, Christian Eigenbrod, Nikolay Smirnov, Osamu Fujita, Adam Cowlard, Sebastian Rouvreau, Grunde Jomass, "Development of Large-Scale Spacecraft Fire Safety Experiments", 43rd International Conference on Environmental Systems, International Conference on Environmental Systems (ICES), paper: AIAA 2013-3410, Vail, Co, USA July 14-18, 2013

6) "NASA Pursues Burning Desire to Study Fire Safety in Space," NASA, Release 16-006, March 16, 2016, URL: http://www.nasa.gov/press-release/nasa-pursues-burning-desire-to-study-fire-safety-in-space

7) "Spacecraft Fire Experiment-I (Saffire-I)," NASA News, Jan. 13, 2016, URL: http://www.nasa.gov/mission_pages/station/research/experiments/1761.html

8) Cheryl Warner, Dan Huot, "NASA Sends Fire, Meteor Experiments to International Space Station on Commercial Cargo Spacecraft," NASA, Release 16-036, March 23, 2016, URL: http://www.nasa.gov/press-release/nasa-sends-fire-meteor-experiments-to-international-space-station-on-commercial-cargo

9) Steven Siceloff, "Cygnus Cargo Ship, Atlas V Blaze Path to Station," NASA, March 23, 2016, URL: http://www.nasa.gov/feature/cygnus-cargo-ship-atlas-v-blaze-path-to-station

10) Kathryn Hambleton, Tracy Young, "NASA TV Coverage Set for Fifth Orbital ATK Resupply Mission to Space Station," NASA, March 17, 2016, URL: http://www.nasa.gov/press-release/nasa-tv-coverage-set-for-fifth-orbital-atk-resupply-mission-to-space-station-0

11) Steven Siceloff, "Cygnus Set to Deliver Its Largest Load of Station Science, Cargo," NASA, March 18, 2016, URL: http://www.nasa.gov/feature/cygnus-set-to-deliver-its-largest-load-of-station-science-cargo

12) "Sticky, stony and sizzling science launching to space station," Science Daily, Source NASA/JSC, March 9, 2016, URL: https://www.sciencedaily.com/releases/2016/03/160309140040.htm
 


The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).

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