# Presentation: 502359

## Section 6

_***Section 6***_
***Risk Mitigation Considerations***

***. . . Edmund H. Conrow***
*Independent Consultant*

## Some Risk Balancing Observations

***Some Risk Balancing Observations***

***FMEA, Fault Tree Analysis, and Probabilistic Risk Analysis involve a common observatory (spacecraft and payload structure)***
***No disconnects identified at this time***
***Permits a meaningful analysis of residual risk for the EO-1 Minimal Mission***
***Enables a quantitative risk assessment as requested by the NASA Administrator***

## Residual Risk MitigationConsiderations (1 of 5)

***Residual Risk Mitigation******Considerations (1 of 5)***

***Mission Science Validation:***
***Initially obtain growing season data over selected southern hemisphere sites in an accelerated fashion***
***Provides an “early growing season” (vs. northern hemisphere starting in March)***
***High probability of achieving the Minimal Mission in 4 months***
***Examine spacecraft and ALI subsystems to identify possible functionally redundant areas that will effectively provide increased operational reliability***
***Examples identified for:***
*Attitude Control  Subsystem (ACS)*
*Communications Subsystem (CS)*

## Residual Risk MitigationConsiderations (2 of 5)

***Residual Risk Mitigation******Considerations (2 of 5)***

***ACS Contingency Areas***
***Loss of Star Tracker can be mitigated by use of three-axis magnetometer (TAM)***
*Idea based on recent GSFC research*
*Calibrate the TAM with the Star Tracker during the first week on orbit*
*Could subsequently use TAM data if the Star Tracker failed*
*Depending on the S/C magnetic cleanliness aloft, initial pointing accuracy will be at least 1.0 degree*
*Subsequent pointing accuracy should approach 0.1 degree vs. 0.02 degree with Star Tracker*
*TAM data normally part of telemetry stream*
*Use ground processing to derive results and uplink to spacecraft*
*Possibility of moving the calculations to the spacecraft after several months*
***Loss of IRU can be mitigated by use of the Star Tracker***
*Normally calculate rates from the Star Tracker and IRU*
*Could use Star Tracker data to augment remaining gyros for inertial reference*
*Possibility of flying spacecraft using Star Tracker, TAM, and GPS without IRU*
*Involves software patch uploaded from the ground*

**6 - **

## Residual Risk MitigationConsiderations (3 of 5)

***Residual Risk Mitigation******Considerations (3 of 5)***

***CS Contingency Areas:***
***S-Band transmitter is functionally redundant to the X-Band capability***
***Involves software patch uploaded from the ground***
***Will not affect loss of S-Band receiver that is fatal***

## Residual Risk MitigationConsiderations (4 of 5)

***Residual Risk Mitigation******Considerations (4 of 5)***

***Other failures may still permit EO-1 operation:***
***Command and Data Handling***
*Housekeeping RSN essential only through Solar Array deployment*
***WARP***
*Power filter box*
*Little or no loss of function if unit fails, but still conducts*
*RS-422*
*Can lose some of the individual lines with minimal performance impact*

## Residual Risk MitigationConsiderations (5 of 5)

***Residual Risk Mitigation******Considerations (5 of 5)***

***Other failures may still permit EO-1 continued operation***
***ALI***
*FPE*
*Failure in an SCA channel could be tolerated*
*However, failure in infrastructure circuitry (e.g., common clock) leads to FPE failure*
*ALICE*
*Might perform mission based upon remaining functions following a partial failure*
*Detailed diagnostics not available (as with the WARP memory interface board -- no M5 processor)*

## Interaction of Launch Vehicle &Mission Reliability (1 of 2)

***Interaction of Launch Vehicle &******Mission Reliability (1 of 2)***

***Overall mission reliability includes both Launch Vehicle and observatory reliabilities***
***ELV reliability of ~ 0.8 to 0.9 over the past 3 years***
***Reliability of some ELVs worse than this***
***Very high Delta 2 reliability (>0.98) greatly benefits EO-1***
***Benefit is more so than realistic set of reliability upgrades possible to EO-1 itself at this time***

## Interaction of Launch Vehicle &Mission Reliability (2 of 2)