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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
Cabin Environment Physics Risk Model!!Chris Mattenberger, Science & Technology Corporation!Donovan Mathias & Susie Go, NASA ARC!Engineering Risk Assessment Team!NASA Ames Research Center, Moffett Field, California!!
!Applied Modeling & Simulation (AMS) Seminar Series!
NASA Ames Research Center, October 7th, 2014!!
! ! ! ! ! !!
Overview!
• Engineering Risk Assessment Team Introduction
• Probabilistic Risk Assessment Methodology
• Cabin Environment Physics Risk (CEPR) Model
• Application of CEPR Model to Generic ISS Mission Architecture
• “Blow and Bleed” Sensitivity Study
• “Feed the Leak” Sensitivity Study
• Risk-Informed Design Examples
• Summary and Conclusions
2
– 7th and 8th Workshops on Probabilistic Risk Assessment
Methods (PRAM)!– PRA Handbook!
– Simulation-based modeling techniques and their application to PRA !
ERA Programs & Projects!
SLS Ares LSS
Mars
OSMA
– Blast overpressure, debris, fireball physics modeling!
– Ascent abort effectiveness assessment!
– Campaign analysis, long-term operations and repair!
– LOM/LOC and availability estimates!
– Campaign analysis!
ERA also supports analysis of satellites, sample return missions and asteroid defense!3
ERA Team Philosophy!
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• Risk-informed decision support − Requirement verification − Risk-informed design support − Part selection/procurement
• Probabilistic risk assessment is informative, not predictive − Provides quantitative answers to
specific questions − Always driven by specific application − Based on traditional methods and
extended as appropriate
Pessimistic bounds!
Architecture! Model inputs!
Physical model!
Assess risk drivers!
Risk acceptable?!
Solution reached!
Assumption driven?!
Architecture driven?!
Refine inputs
Design trades
Iterative/responsive modeling approach
Risk model maturity tracks design maturity and engages engineers early in the design process, rather than a post facto analysis!
ERA Team Methodology!
• Dynamic nature of failures − Time dependence − State dependence − Partial & interactive failures
• Physics-based analysis − External hazards − Failure evolution
• Traditional static models − Lower part levels − Typically reliability based
Combines traditional PRA methods with dynamic methods for increased accuracy of representation of system risk!
tetR λ−=)(
5
Cabin Environment Influence Diagram!
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Cabin environment is impacted by many traditional spacecraft subsystems!
Cabin Environment Physics Risk (CEPR) Model!
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• Estimates time interval from loss of functionality to hazardous environment Estimates time from loss of functionality to onset of hazardous environment!
CEPR Model Implementation in GoldSim!
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GoldSim provides a graphical representation of data flow within model!
Loss-of-Crew Threshold Tracking!
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CEPR tracks partial pressures of key cabin atmospheric constituents!
nRTPV =
Avionics & PCS Implementation!
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CEPR model captures dynamic interaction of spacecraft subsystems!
PPRV Implementation!
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CEPR model captures physics-based impacts of component functionality!
ERA Generic Launch Vehicle & Spacecraft!
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!!
!!!!
Liftoff Cape Canaveral t = 0 sec
1st Stage Separation Alt = 80 km t = 181 sec
LAS Jettison Alt = 117 km t = 211 sec
2nd Stage Separation and Orbit Insertion Alt = 350 km t = 560 sec
Earth Orbit TOF: 24 hrs
ISS Dock Duration: 6 months
Undock, Prep & Cold Soak TOF: 3 hrs
De-Orbit Burn 60 min to touchdown
Alt: 300 km
Entry Interface & SM Jettison 30 min to touchdown
Alt: 200 km
Parafoil Deployment 2 min to touchdown
Alt: 5 km
Land Ocean splashdown or
ground landing
Mission concept of operations used to demonstrate CEPR model implementation!Conceptual Launch Vehicle and Spacecraft Design for Risk Assessment, NASA/TM-2014-218366
Assumptions!
• Cabin Properties − 16 m3 air volume − Leakage rate of 0.036 lbm/day − 297 K constant temperature − Perfectly controllable O2 mass
flow rate and O2 sensors − Perfect pressure vessel − Perfect Mixing − Ideal Gas
• Initial Nominal Cabin State − 3.234 psi ppO2
− 0.058 psi ppCO2
− 11.408 psi ppN2
• Crew – 4 Crew – Consume 0.2434 kg/hr of O2
– Produce 0.2554 kg/hr of CO2
• Consumables – 44.7 kg of O2 at 100% Full – 167 kg of N2 at 100% Full – 297 K constant temperature
• LiOH Canisters – Removes 0.2554 kg/hr of CO2 at
100% effectiveness level • LOC Thresholds & Return Time
– Minimum ppO2 is 2.3 psi – Maximum ppCO2 is 0.87 psi – Return Time is 4 Hours
Green indicates Simplifying Assumption / Blue indicates Uncertain Assumption / Black indicates Uncertain Design Requirement
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Design Insights for Risk-Informed Decisions:“Blow and Bleed” Sensitivity Study!
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CEPR model yields design insights to inform mission rules!
0.1
1
10
100
1000
100% 80% 60% 40% 20% 0%
Tim
e to
LO
C [h
r]
Percent Scrubbing Effectiveness
Time to LOC vs. %CO2 Scrubbing ppCO2 = 0.87 psi
0% Tank Remaining
20% Tank Remaining
40% Tank Remaining
60% Tank Remaining
80% Tank Remaining
100% Tank Remaining
Abort from Orbit - 4 hrs
)1()1(
12 −
+
⎟⎟⎠
⎞⎜⎜⎝
⎛
+=
γγ
γγρPCAm!
Design Insights for Risk-Informed Decisions:“Feed the Leak” Sensitivity Study!
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CEPR model yields design insights to aid in risk-informed decision making!
0.1
1
10
100
1000
0 5 10 15 20 25
Tim
e to
LO
C [h
r]
Leakage Rate [kg/hr]
Time to LOC vs. Leakage Rate ppO2 = 2.3 psi
0% Tank Remaining
20% Tank Remaining
40% Tank Remaining
60% Tank Remaining
80% Tank Remaining
100% Tank Remaining
Abort from Orbit - 4 hrs
)1()1(
12 −
+
⎟⎟⎠
⎞⎜⎜⎝
⎛
+=
γγ
γγρPCAm!
Dynamic Mission Risk Model!
Integrated dynamic risk model captures time- and state- dependent behavior!16
Dynamic Risk Model Integration!
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Monte Carlo simulation enables CEPR results to impact overall mission risk!
180 hr
4 hr
0 hr
Risk-Informed Design Example: Risk Driver Ranking!
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0.00E+00 1.00E-04 2.00E-04 3.00E-04 4.00E-04 5.00E-04 6.00E-04 7.00E-04
Avionics Communications & Tracking
ECLSS Electrical Power
Events & Hazards Launch Vehicle Equipment
Mechanisms Propulsion
Thermal Control
Risk of LOC
Spac
ecra
ft Su
bsys
tem
ERA Spacecraft LOC Risk Drivers
LOC
LOC - CEPR
0.00E+00 2.00E-03 4.00E-03 6.00E-03 8.00E-03 1.00E-02 1.20E-02
Avionics Communications & Tracking
ECLSS Electrical Power
Events & Hazards Launch Vehicle Equipment
Mechanisms Propulsion
Thermal Control
Risk of LOM
Spac
ecra
ft Su
bsys
tem
ERA Spacecraft LOM Risk Drivers
LOM
LOM - CEPR
Excessively conservative assumptions can impact relative risk results!
Risk-Informed Design Example: Risk Reduction Trade Study!
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EPS - Enhanced Mass [lbs] ECLSS - Enhanced Mass [lbs]Fuel Cell Stack 10.7 Manual Valve 0.3Heater 1 Manual Valve 0.3Heat Exchanger 0.65 Manual Valve 0.3Pressure Regulator 0.635 Manual Valve 0.3Pressure Sensor 0.22 Manual Valve 0.3Hydrogen Purge Valve 0.1 Manual Valve 0.3Water Separator 0.5Total Mass Delta 13.805 Total Mass Delta 1.8
Trade Study Options
EPS ECLSS
Risk-Informed Design Example: Risk Reduction Trade Study!
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• Excessively conservative assumptions can alter trade study results dramatically Excessively conservative assumptions can alter trade study results dramatically!
0.00E+00
1.00E-05
2.00E-05
3.00E-05
4.00E-05
5.00E-05
6.00E-05
7.00E-05
8.00E-05
9.00E-05
1.00E-04
0 2 4 6 8 10 12 14 16
Ris
k of
LO
C
Delta-Mass [lbs]
LOC Risk Reduction Trade Study
ECLSS - Baseline
ECLSS - Enhanced
EPS - Baseline
EPS - Enhanced
ECLSS - Baseline - CEPR
ECLSS - Enhanced - CEPR
Risk Reduction Efficiency = ΔRisk / ΔMass
Summary & Conclusions!
• CEPR model is used to predict the time for an initial ECLSS failure to propagate into a hazardous environment and trigger a LOC event − Can be utilized as a stand-alone model to aid in decision-making − Allows for integration of model results into dynamic mission risk models − Enables the risk analyst to remove the assumption that loss of functionality triggers LOC
• The assumption that loss of functionality triggers LOC has been shown to be excessively conservative − Impacts overall risk driver ranking − Impacts risk reduction trade study results − Could lead to a suboptimal design that inherently increases the risk of LOC
• Incorporating CEPR results yields more accurate design insights
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Future Work!
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