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Dezfuli.homayoon

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  • A Concept of Operations (abbreviated CONOPS or ConOps) is a document describing the characteristics of a proposed system from the viewpoint of an individual who will use that system.It is used to communicate the quantitative and qualitative system characteristics to all stakeholders. CONOPS are widely used in the military or in government services, as well as other fields.
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    • 1. NASA‟s Safety Goal Policy for Human Space(Key Concepts Behind the Policy, Implementation Approach Through a Risk-informed Safety Case) Presented at the NASA Project Management 2011 Conference Long Beach, California February 9-10, 2011 Homayoon Dezfuli, Ph.D. NASA Technical Fellow (System Safety) Office of Safety and Mission assurance (OSMA) NASA Headquarters
    • 2. Acknowledgments• This presentation has benefited substantially from the System Safety Handbook development work supported by – Robert Youngblood, Idaho National Laboratory (INL) – Curtis Smith, INL• The presentation has also benefited from discussions with my OSMA colleagues – Michael Stamatelatos – Frank Groen – Alfredo Colon 2
    • 3. Outline• Background• The Concept of Safety Thresholds and Goals• Overview of the Risk-Informed Safety Case (RISC)• Summary 3
    • 4. BACKGROUND 4
    • 5. Aerospace Advisory Safety Panel(ASAP) Recommendation 2009-01-02a• The ASAP recommends that NASA stipulate directly the HRR acceptable risk levels—including confidence intervals for the various categories of activities (e.g., cargo flights, human flights)—to guide managers and engineers in evaluating “how safe is safe enough.” These risk values should then be shared with other organizations that might be considering the creation of human-rated transport systems so that they are aware of the criteria to be applied when transporting NASA personnel in space. Existing thresholds that the Constellation Program has established for various types of missions might serve as a starting point for such criteria.• NASA Accepted the recommendation and committed to developing a safety goal policy for the human space flight. 5
    • 6. THE CONCEPT OF SAFETYTRESHOLDS AND GOALS 6
    • 7. Safety Thresholds and Safety Goals• In our response to ASAP we said – Safety Goals are desirable safety performance levels for driving safety improvements – Safety Thresholds are criteria for risk acceptability decisions; not meeting these values is not tolerable – Both goals and thresholds are defined by Agency in terms of aggregate risks – The safety goal and threshold collectively • Help designers with safety performance allocation • Help decision makers to deal with safety-related decisions - Risk acceptance - Risk mitigation - Safety optimization 7
    • 8. Safety Regimes and Safety Decisions tobe Made Standard of “Optimally and Sufficiently Safe” Standard of “Minimally Safe Level” More than this May have diminishing return Less than this would be “intolerable” GOAL TRESHOLD Frequency Threshold (to be met with ≥ X% probability) SAFE ENOUGH TOLERABLE INTOLERABLE Optimization Mitigation Aggregate Frequency of Scenarios Leading to Loss of Crew Increase in Decision Flexibility • Keep alert for • Actively pursue safety • Don‟t proceed with enhancements, but improvements via risk the acquisition focus more on tradeoff studies • Fix design or maintaining the good • Actively identify operation to meet safety level that has unaccounted-for hazards via the threshold been been achieved precursor analysis 8
    • 9. OVERVIEW OF THE RISK-INFORMEDSAFETY CASE (RISC) 9
    • 10. Practical Implications of SafetyRequirements Based on Risk Metrics• We cannot “prove” ahead of time that the fraction of launch failures in the limit of a large number of launches will be < X• The „case” that P(event) < X needs to be supported by a coherently-stated rationale providing both narration and evidence that justifies the level of safety claimed – Evidence includes operating experience, tests, integrated safety analysis, etc.• Risk-informed Safety Case (RISC): A documented body of evidence that provides a convincing and valid argument that the system is adequately safe 10
    • 11. Risk-informed Safety Case (RISC)• “Adequately safe for a given application in a given environment:” – Safety Goal – Other Safety Requirements• To develop a safety case we need to: – Make an explicit set of claims about the system(s) • E.g., probability of accident is low – Produce supporting evidence of sufficient caliber • E.g., operating history, redundancy in design, … – Provide a set of safety arguments that link claims to evidence – Make clear assumptions and judgments underlying the claims – Allow different viewpoints and levels of detail• Part of the evidence comes from Probabilistic Safety Analysis (PSA): Scenarios, Frequencies, Consequences – Reliability aspects – Phenomenology aspects (e.g., analysis of abort effectiveness) – Operational and human error aspects 11
    • 12. Pointillism vs. Coherent Safety Picture System safety perspective needs to be integrated and coherent, as opposed to apointillistic portrayal of hazards and controlsPointillism is a style of painting in which small distinct points of primary colorscreate the impression of a wide selection of secondary colors. The techniquerelies on the perceptive ability of the eye and mind of the viewer to mix thecolor spots into a fuller range of tones. Source: Wikipedia 12
    • 13. The Coherent Case that Needs to beMade to the Decision-Maker 13
    • 14. Safety Case is a Basis for Decision-making anda Roadmap for Implementation• To decision makers, the safety case shows how the designers have met their challenge, and why the design should be approved – It relates the design characteristics to the safety performance, and shows what processes were followed• To implementers (construction, manufacturing, installation, maintenance), it shows what they have to do and how well they have to do it – What functions have to be maintained, what performance allocations need to be satisfied• To operators (astronauts, launch decision-makers), it shows how to remain safe in flight – It defines the operational envelope inside which operational freedom is permitted – Penetration of the envelope calls for changes to design or operation, and/or reanalysis 14
    • 15. Evolution of the Risk-Informed Safety Case (RISC)over the Life Cycle Safety Requirements Input to Design Safety CasePerformed by • Safety Goals AcceptanceNASA • Safety Requirements • Technical Requirements • Very high confidencePerformed by • Process Requirements that system meets theProvider • Analysis Protocols and tools for Safety threshold Requirement Demonstration and Optimization • High confidence thatPerformed jointly system is optimally safe Deployment Development of RISC Optimization/ Risk Management Trending of Safety Develop & Justify Performance Performance Commitments Design Integrated Safety Analysis of Operating Operation Experience / Precursor Analysis Risk-Informed Tolerable Analysis Identification of Hazards & Safety Case Region Associate Risks Demonstrate Identification of Satisfaction of Controls Safety Requirements Intolerable Based on Integrated Safety Analysis / Region Operating Optimization Optimization Input Experience Input Performance Feedback
    • 16. Raising the Bar for Safety Performance(notional) First Second group of Third group of Flight Flights (2-5) Flights (6-10)Optimization RISC for RISC for Region Flights Flights > 10 RISC for 6-10 Flights RISC for 2-5 First FlightTolerable RegionIntolerableRegion 16
    • 17. Role of System Safety in Developing theRISC Key Claims of Safety Case • Design Specification • ConOps, Design intent, & Design Safety Requirements specified “completely” for current design phase • Systematic Process to ID Hazards • Comprehensive Hazard Identification Process has been Design, ConOps, … implemented based on ConOps, Design Intent, Design • Identified Hazards Controlled • For each hazard, either a design change has been made, or {(Hazardi, Control(s)i)} appropriate controls have been identified for each hazard, and resources have been allocated to implement those controls • Aggregate Risk OK Risk ~ • Aggregate risk considerations are {Scenarioi, Likelihoodi, Co satisfied, and there are no known nsequencesi} additional cost-beneficial controls or design modifications 17
    • 18. Role of Scenario-Based Probabilistic Safety Analysis (PSA) in Formulation of the RISC • Probabilistic Safety Analysis” refers to a structured, probabilistic treatment of scenarios, likelihoods, consequences • Probabilistic Safety Analysis quantifies risk metricsThe Risk-informed Safety Case is notthe PSA Rather LOC Probability Mitigation/abort Severity (failure environment)• The PSA is a thought process used to Warning time Type of environment (LOC env) Detection guide formulation of the RISC S Magnitude • Sensor D • Trigger value Failure propagation Failure (amplification, cascade, • A convincing hazard analysis can help to propagation C evolution) time E • PDA • SARA Operational state (MET) make the case that the problem is well Active thermal control E system fails to provide cooling (phase 3) ATCS_TOP_P_3 C The ATCS fails (phase 8) Failure to provide power (phase 3) Electric power system control fails (phase 3) understood ATCS_FAILS ATCS_EPWS_POWER_P_3 ATCS_EPWS_CONTROL_P_3 N I Heat collectors fail (phase 8) Heat transporters fail (phase 8) CEV ATCS CM ATCS-HSNK-FTF-EVAP-P-3 1.09E-05 No power from electric power system fails ATCS No signal from Avionics System fails ATCS • The scenario set developed in the PSA (phase 3) ATCS_EPWS_BE_P_3 5.00E-06 (phase 3) 1.00E-04 ATCS_AVCS_BE_P_3 ATCS_HEAT_COLL ATCS_HEAT_TRANS CEV ATCS CM Coolant ATCS-TANK-FTF-CM-P-3 1.09E-05 CEV ATCS CM heat A ATCS-HCOL-FTF-CCF-P-3 8.37E-06 CEV ATCS CM Heat CEV ATCS CM Heat CEV ATCS CM heat S ATCS-HCOL-FTF-1-P-3 8.37E-05 ATCS-HTRN-FTF-1-P-3 3.64E-08 transport devices CCF CEV ATCS CM Heat CEV ATCS CM Heat (phase 3) 3.64E-09 Pr( ) ATCS-HTRN-FTF-CCF-P-3 Collection Devices (Loop Transport Devices (Loop 2) (phase 3)8.37E-05 2) (phase 3)3.64E-08 can be used by designers to establish ATCS-HCOL-FTF-2-P-3 ATCS-HTRN-FTF-2-P-3 R T = 0.0 EDS, LSAM, and CEV in Depart Earth to Low LSAM Performs Lunar CEV In Lunar Orbit # End State I LEO Lunar Orbit Orbit Injection Injection (Phase - PH1) LAUNCH PHASE_1 PHASE_2 PHASE_3 PHASE_4 what allocation of functional 1 MOON_TO_EARTH Bayesian I 2 LOM_OR_LOC capability, physical O 3 4 LOM_OR_LOC LOM_OR_LOC Probabilities margin, redundancy, and element N If explosion then 5 LOM_OR_LOC O reliability can best satisfy safety targets S if launch_abort > 0.1 then … else if S …. within real-world constraints …. • Success paths credited to meet safety End if targets are the appropriate conceptual framework for narration of the safety Probabilistic Risk Analysis Probabilistic Safety Analysis case 18
    • 19. SUMMARY 19
    • 20. Summary• Safety Goals and Thresholds will change the way in which System Safety work is carried out and used. They: – Are tools for implementing agency safety policy – Will be used to guide design and system safety analysis – Will play a key role in acquisition• Safety goals and thresholds require integrated systems view of system safety• The major product of System Safety is the RISC• The RISC is meant to show why a DM can have confidence in a decision to proceed, and what has to be made to come true in order to maintain that confidence• The RISC brings together a diversity of evidence and analysis to support a hierarchy of technical findings – Integrates the traditional piece parts of System Safety processes• High-level PSA results are part of the RISC, but PSA is not the sole reason for confidence in the conclusion – It is a tool for achieving integrated perspective 20
    • 21. Summary (Cont.) • To decision makers, the RISC shows how the designers have met their challenge, and why the design should be approved – It relates the design characteristics to the safety performance, and shows what processes were followed • To implementers, RISC shows what they have to do and how well they have to do it – What functions have to be maintained, what performance allocations need to be satisfied • To operators (astronauts, launch decision-makers), RISC shows how to remain safe in flight – It defines the operational envelope inside which operational freedom is permitted • Penetration of the envelope calls for changes to design or operation, and/or reanalysis • Changes in design or operation that would alter the RISC would alter the basis for decisions, and correspondingly need review and re- acceptance 21

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