This slide presentation reviews the use of ground test data in reference to flammability  to spacecraft environments.  It reviews the current approach to spacecraft fire safety, the challenges to fire safety that the Constellation program poses, the current trends in the evaluation of the Constellation materials flammability, and the correlation of test data from ground flammability tests with the spacecraft environment.  Included is a proposal for testing and the design of experiments to test the flammability of materials under similar spacecraft conditions

Beeson, Harold

Hirsch, David

Williams, Jim

NASA Technical Reports Server

Slide 1
Applicability of Aerospace Materials 	 l
Ground Flammability Test Data to
Spacecraft Environments
Theory and Applied Technologies
David Hirsch
Jim Williams
Harold Beeson
NASA White Sands Test Facility
Las Cruces, New Mexico
USA
Technical Interchange Meeting on Aerospace Materials Flammability
German Aerospace Agency
Bremen, Germany
October 2009
Slide 2
• Current approach to spacecraft fire safety
• Constellation Program fire safety challenges
• Current trends in evaluation of Constellation materials
flammability
• Correlation of ground flammability test data with
spacecraft environments
https://ntrs.nasa.gov/search.jsp?R=20090036308 2019-08-30T08:08:35+00:00Z
Slide 3
• General Strategy: Prevent Fires
• Control materials
• Minimize potential ignition sources and materials that
can propagate a fire
• Control the quantity and configuration of flammable
materials to eliminate fire propagation paths
Slide 4
• Major flammability tests – NASA STD 6001.A Tests 1
and 4
• Upward flame propagation
• Conducted under worst-expected spacecraft conditions,
usually in 30% oxygen at 10.2 psia
• Pass/fail test logic
Discuss:
materials passing criteria (pass/fail approach) - qualitative
ignition source - simulates a worst case
testing in the "worst" case expected, usually 30% oxygen, 10.2 psia - explain (pre-EVA operations)
note that the pass/fail logic assumes a direct correlation between 1-g data and flammability behavior in
spacecraft environments.
Slide 5
• Long duration; unplanned events more likely
• Limited options for mission termination
• Variety of spacecraft, surface habitats, planetary landers
• Spacecraft environment and its importance
• Flexibility and adaptability critical for success
Current safety design challenges:
ECLSS designed to handle a CM leak equivalent to 1/4-in. diameter for an hour
Unplanned transitory events:
Crew Module (CM) depressurization - real event in ISS during late 2002
Loss of nitrogen - will drive the need to know what max oxygen concentration we can expose the CM to
and still manage fire risks;
Frequency and duration of EVAs will increase, so there may be an increase in emergency rescues of an
astronaut in EVA distress; need the capability to respond quickly to EVA emergencies
Increasing communication delays
The MIR fire of 1997
Limited options for mission termination:
a salvageable event in Earth orbit could be catastrophic during most of the transitory Earth-Mars voyages;
the result could be loss of crew and mission.
Flexibility in selecting different environments for various spacecraft, surface habitats, planetary landers,
or pressurized extraterrestrial rovers will allow flexibility in space system design and operation. The
complexity of space system design often requires changes to mitigate various safety issues, financial
impacts, and so on. Design and operational flexibility could result in increased ability to mitigate hazards
or develop superior systems with less financial burdens. For example, retesting of materials will not be
required if new spacecraft conditions are selected.
Slide 6
• Air velocity magnitude contours at aft-forward mid-section of
the U.S. Airlock Module
– Courtesy: Son, C.H., et al, Integrated Computational Fluid Dynamics
Ventilation Model for the International Space Station, SAE Technical
Paper 2005-01-2794, Society of Automotive Engineers, 2005
Space system environments
Range of gravities - large at launch, microgravity during interplanetary travel, reduced gravity on the
Moon and Mars
Ventilated environment, for mixing and spacecraft skin temperature control; for example, a velocity
magnitude of up to 20 cm/s is encountered in 75% of the U.S. Airlock. Velocities up to 100 cm/s are also
encountered.
Range of oxygen concentrations and total pressures for various operations (i.e., pre-EVA acclimatization
to prevent decompression sickness) - with the oxygen partial pressures kept above the hypoxic levels and
oxygen concentrations below what is believed to be the materials’ flammability level (subject to epistemic
uncertainty)
Slide 7
Slide 8
• 1-g Constellation materials flammability qualification
tests conducted at NASA WSTF determine the oxygen
concentration flammability extinguishment limits
• NASA WSTF also conducted a series of tests to
evaluate total pressure effects on the flammability
threshold
The tests conducted at WSTF will allow flexibility in spacecraft environment selection. For example, we
are contemplating having environments of up to 34% in the Lunar surface habitation modules; the
oxygen-enriched environments require less nitrogen and would minimize the acclimatization time
required for astronauts prior to an EVA. A practical application example of knowing the pressure effects
on the flammability threshold is establishing the internal pressure limit for landing spacecraft at KSC. The
WSTF data in corroboration with flammability threshold data in spacecraft environments will allow us to
determine fire safety factors. American microgravity test facilities initiated flammability threshold testing
following the WSTF approach. In the long term, we will be able to have accurate fire risk assessments,
which will allow proper mitigation. As a consequence, we will be able to achieve increased spacecraft fire
safety.
Slide 9
• Likelihood of fire events, with limited options for mission
termination, will increase with longer duration space
missions.
• Rigorous correlations between 1-g ground materials
flammability qualification test data with data in ventilated
microgravity environments of spacecraft will lead to
realistic evaluations of proper fire safety factors and
spacecraft fire risks.
Unexpected space mission events could challenge space system fire safety design boundaries.
Correlations of 1-g flammability test data relies on many assumptions, some of which may not stand up to
future findings.
Slide 10
• Understanding fire risks in transient spacecraft
environments will allow flexibility in spacecraft design
and operability.
• NASA White Sands Test Facility (WSTF) currently works
with NASA Glenn Research Center (GRC) on ground
flammability test qualification data correlation with data in
Lunar surface habitation environments.
Operational flexibility is of critical importance for advanced space programs relying on integrated designs
extending across multiple vehicle atmospheres and focusing strongly on crew safety and operational
effectiveness.
In the future, we’ll need to work on reducing the epistemic uncertainty related to space system
fire safety factors and fire risks in various space vehicles, Lunar and Mars surface habitats,
planetary landers, pressurized extraterrestrial vehicles, and other space systems.
Slide 11
Partial gravity centrifuge installed in the NASA GRC
Zero Gravity Facility drop bus
Slide 12
NASA GRC and WSTF proposed a comprehensive
program on correlating 1-g flammability threshold data
with a variety of spacecraft-specific environments
(response to a NASA Research Announcement)
– Oxygen concentration and pressure effects
(prevalent, transitions, extremes)
– Ventilation effects (0 to 1 m/s)
– Microgravity or partial gravity effects
Slide 13
Materials with oxygen concentration thresholds in the
25 to 35 range will be tested
Most oxygen concentration flammability thresholds will
be evaluated at the spacecraft prevalent pressure
(14.7 psia)
Further 1-g tests will focus on the immediate
post-ignition and extinguishment flammability behavior to
attempt determination of a pass/fail criteria amenable to
the short duration of ground microgravity tests
Slide 14
• Most reduced gravity and
microgravity testing will be
conducted in parabolic
aircraft flights
• Approximate test time: 22 s
• The NASA GRC
microgravity wind tunnel
will be modified for
parabolic flights
Slide 15
Slide 16
• Flow velocities of 0 to 30 cm/s while maintaining the total
test chamber pressure constant
Total pressure range: 0-14.7 psia
Oxygen concentration range: 0-100% oxygen
Slide 17
• Under set conditions (prevalent spacecraft pressure,
commonly encountered surface flow velocities of
30 cm/s), determine the oxygen concentration
flammability threshold in reduced gravity and
microgravity
• Current limited data indicates that somewhere between
zero and 30 cm/s flow velocities the 1-g data becomes
less conservative than data in microgravity and reduced
lunar gravity
Slide 18
Continue oxygen concentration flammability threshold
measurements at lower velocities until a flammability
velocity threshold is obtained where the oxygen
concentration thresholds in 1-g and microgravity coincide
Build a flammability threshold map and compare
microgravity and 1-g threshold limits. The data will allow
to evaluation of the level of conservativeness (or the lack
of it) of 1-g data (“safety factors”)
Slide 19
Computational Fluid Dynamics (CFD) of spacecraft flow
velocities will identify zones where 1-g materials
qualification data is not conservative and if ignition
occurs, flame propagation would be possible. This will
provide information for ventilation design to improve
spacecraft fire safety.
Knowing parametric effects on the flammability threshold
will allow effective spacecraft fire risk management.
Slide 20
• Verification flight experiments in the International Space
Station Combustion Module will be conducted
• Flammability threshold maps will be determined to
validate the ground microgravity testing approach for
several materials
• The information obtained will be correlated with materials
characteristics to predict flammability thresholds for other
aerospace materials
• In the long term, we’ll have comprehensive mapping of
spacecraft flammability hazards and associated risks.


Applicability of Aerospace Materials Ground Flammability Test Data to Spacecraft Environments Theory and Applied Technologies

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