# Presentation: 522009

## Section 3

_***Section 3***_
***Residual Risk***

*** ******. . . Bryant Cramer***
*EO-1 Mission Implementation Manager*

## Contents

***Contents***

***Definition of residual risk***
***Red Team focus on residual risk***
***Probabilistic assessment of the EO-1 design***
***Survey of residual risk on EO-1***

## Residual Risk

***Residual Risk***

***Residual Risk is that risk remaining at launch after all mitigation efforts have been completed***
***The Red Team is charged to “ascertain and document all residual risks, judged to be any level higher than low, that are remaining in the mission”.***
***Administrator has asked that 3 system engineering tools be used to estimate the likelihood of occurrence and the overall mission risk associated with the predominant failure modes as identified by:***
***Failure Modes and Effects Analysis***
***Fault Tree Analysis***
***Probabilistic Risk Analysis***
***Red Team Charter focuses on single-point failure mechanisms as a major source of residual risk***

## Single String Design

***Single String Design***

***EO-1 is intentionally single string***
***EO-1 is a technology validation mission. Compared to a small science mission, there is:***
***Shorter life on orbit -- usually a few months***
***Lesser dependence on flight data -- extensive ground-based validations of the assigned technologies have already been completed***
***Necessity of a timely validation -- desire to maximize technology infusion opportunities***
***Single string designs offer the following benefits:***
***Less complexity***
***Shorter schedule***
***Lower cost***
***Red Team specifically requested to comment on the suitability of single string designs for technology validation missions***

***But with numerous single point failures***

## Sources of Residual Risk

***Sources of Residual Risk***

***Those inherent in the design of the system:***
***Instruments***
***Spacecraft***
***Launch***
***Operations***
***Those associated with the processes used to integrate and test the flight hardware and software***
***Those associated with problem-solving at any point in the developmental process***
***Those inherent in the parts and materials used to build flight hardware***
***Those attributable to workmanship and quality control***
***Those associated with waivers***
***Those associated with training and operations***

## Three System Engineering Tools

***Three System Engineering Tools***

***Administrator has asked that we evaluate residual risk through the use of:***
***Failure Mode and Effects Analysis (FMEA)***
***Failure Tree Analysis (FTA)***
***Probabilistic Risk Analysis (PRA)***
***These are normally used during design definition to support the system engineering process***
***These tools were not used to develop the EO-1 design:***
***Single string design by policy***
***Hard cost cap and lots of schedule pressure***
***Redundancy was largely out-of-bounds -- by policy, by budget, by schedule, and by available staff***
***We optimized within the existing constraints -- as best we could***
***We propose to use these 3 tools in a complementary abbreviated application to evaluate the likelihood of successfully completing the EO-1 Minimal Mission***
***The results will be presented at the Red Team Follow-up Review***

## EO-1 Minimal Mission

***EO-1 Minimal Mission***

***Described in EO-1 Mission Success Criteria:***
***Our evaluation will focus only on the EO-1 Minimal Mission***

## EO-1 Residual Risk Assessment

***Fault-Tree Analysis:***
*Failure of the Minimal Mission*
*Includes all mission segments*
*Product is mission element failures that disable the Minimal Mission*
***FMEA:***
*Down to box, board or service level, as appropriate*
*Used to survey single-point failures*
*Product is all single-point board failures disabling the Minimal Mission*
***Probability Risk Assessment:***
*Classified by similarity*
*Reliability Block Diagram*
*Product is probability of single-point failures that disable Minimal Mission*

***Strategies for Mitigating More Probable***
***Single-Point Failures***

***Fault Tree Analysis of Minimal Mission***

***Single-Point Failures of Minimal Mission within each Mission Element***

***Probabilistic Classification of Single-Point Failures by Similarity***

***Reliability***
***Block Diagram for Minimal Mission***

***Residual Risk Assessment of EO-1 Minimal Mission***

## Fault Tree Analysis

***Fault Tree Analysis***

***Developed for the EO-1 Minimal Mission***
***Advanced Land Imager***
*Multispectral Imaging Technology*
*Wide Field Reflective Optics*
*Silicon Carbide Optics*
***Wideband Advanced Recorder / Processor (WARP)***
***Nominal spacecraft performance***
***To include the following segments:***
***Flight***
***Ground (including Operations)***
***Launch (mission unique)***
***Proceeds to subsystem level or to board level in some cases***
***Serves to identify the loss of functionality that singularly and independently results in the loss of the EO-1 Minimal Mission***

## Failure Mode and Effects Analysis

***Failure Mode and Effects Analysis***

***Independently developed for the following segments:***
***Flight (all aspects)***
***Ground (including Operations)***
***Launch (provided by KSC)***
***Developed in parallel with the FTA***
***Generally goes to board level***
***Flight FMEA is completed and Ground FMEA is nearly finished***
***By combining the FTA with the FMEAs, we can identify all of the  potential single-point failures in each Mission Element that lead to the loss of the EO-1 Minimal Mission***
***These single-point failures will be discussed by each of the Mission Element presenters at the Red Team Follow-up Review***

## Probability Risk Assessment

***Probability Risk Assessment***

***A reliability estimate will be prepared for each of the single-point failures causing the loss of the EO-1 Minimal Mission***
***These estimates normally involve lengthy calculations based on failure rates of individual parts***
***Time does not allow us to pursue this traditional approach***
***Our estimates will be done at the box or board level based on similarity with earlier projects where detailed reliability calculations already exist***
***These will be integrated into a Reliability Block Diagram identifying the predominant modes of failure for the EO-1 Minimal Mission ***
***Prioritized validation requirements will be plotted against the calculated probability of completing the EO-1 Minimal Mission***
***Strategies will be discussed to better mitigate the likelihood of the predominant failure modes***

## Reliability vs. Mission Success Criteria

## Risk Assessment Schedule

## Survey of Residual Risk

***Survey of Residual Risk***

***Changes and action items are tracked in “community-based” databases***
***There are 8 such databases:***
***Project level:  All system level reviews (including all instruments, spacecraft, technologies, and operations) totaling 403 RFAs***
***Spacecraft:  All Problem Reports totaling 1,563 including all PRs from I&T***
***Flight Software:  Total of 927, usually mirror a corresponding PR***
***Operations:  Total of 194 dealing with the ground system***
***GSFC NCR:  Only used for WARP and AC during their development (46 total) ***
***Materials / Processes:  Total of 161 entries***
***Waivers:  Total of 75***
***Schedule liens:  Total of 60***
***Vast majority (90%) of all changes or action items are in the first 4 databases -- however:***
***Flight Software Problem Tracking Reports generally mirror Spacecraft PRs***
***Operations database deals exclusively with ground system -- no flight hardware involved***
***Consequently, the Project and Spacecraft databases were examined for residual risk candidates***

## Survey of Residual Risk (continued)

***Survey of Residual Risk ****(continued)*

***All of the RFAs were reviewed and 82 were selected to have potential residual risk***
***All of the PRs after starting Thermal/Vacuum were reviewed and classified***
***Any change to flight hardware***
***Any change to flight software***
***Any Redbook candidate***
***Any operational constraint***
***Any open item affecting flight hardware / software***
***Any significant test anomaly occurring during I&T was also selected as a “Special Topic” (57)***
***These 263 residual risk candidates were reviewed and accepted by the GSFC Flight Assurance Office on 3/17/00***
***All of these residual risk candidates will be addressed in the Red Team Review with the mission elements wherein they reside***

***All of these were selected (124)***

## Critical RFAs

***Critical RFAs***

***RFA 1.04:  Define descope options to a Minimal Mission tied to the ALI***
***This has been done and is reflected in the EO-1 Mission Success Criteria***
***A summary of the EO-1 Minimal Mission is presented in this section***
***RFA 1.18:  Establish a requirements configuration control system***
***Draft Level I requirements were established in late 1996***
***Level I requirements were finalized and signed in April 1997 and maintained by HQ***
***A formal requirements traceability effort was undertaken in early 1997 to generate Level II and Level III requirements***
***This process sought to trace all requirements to the technology validation plans***
***Once finished, the Level II requirements were maintained under configuration control by the Project ***
***Level III requirements were maintained by individual developers with Project personnel attending their configuration control boards***

## Critical RFAs (continued)

***Critical RFAs ****(continued)*

***RFA 1.2:  Recommend the use of an FMEA***
***An FMEA is presently in work as a part of the Red Team Preparation***
***RFA 14.14:  Provide a summary of all mission critical PRs***
***The summary is presented in this section along with the process that generated it***
***The more detailed version is a separate document available upon request***