1. Fault Tree Analysis of the HERMES CubeSat
Felix Bidner

2. What is FTA? A form of failure analysis / safety engineering
Takes the form of a logic block diagram
Brief history
- Developed in 1960’s at Bell Laboratories
- Adopted by aerospace industry
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3. What is FTA? Deductive Approach
- Define an undesired state/event in the system and deduce what could lead to that state
Component in B fails
Subsystem B fails
System A fails
Analysis begins
at the undesired state
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4. What FTA Is Not
Not meant to identify all possible failure modes of the system
Only describes the logic leading to a defined top event
Often complemented by inductive analysis such as Failure Modes and Effects Analysis (FMEA)
Not inherently quantitative but can be adapted to be so
If individual event probabilities are known, the probability of the top event can be determined
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5. Why Use It? Identify relationships between subsystems
Determine weaknesses in the system
Prioritize weaknesses by their severity
Prevention & Diagnostics
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6. Fault Tree Symbols
Events
Basic event
Undeveloped Event
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7. Fault Tree Symbols Logic Gates Priority AND AND Exclusive OR OR
Voting OR
AND OR
Transfer Symbol -
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8. Sample Fault Tree Construction
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9. Building a Fault Tree Identify a top event
Assign boundaries to the analysis
Scope
Level of Detail
Perform FTA
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10. Applying FTA to the HERMES CubeSat

11. HERMES Overview
Standard 1U CubeSat as specified by California Polytechnic State University
1 kg, 10 x 10 x 10 cm
Inexpensive to construct and launch
Primary objective is to test high-speed communications in S-band
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12. Divide into Subsystems
ADCS
Attitude Determination & Control
CDH
Command & Data Handling
HSCOM
High Speed Communications
EPS
Power
PCOM
Primary Communications
Structures & Thermal
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13. First Iteration of FTA One top event chosen for each subsystem
Rough outlines of fault trees developed for each top event
What components depend on multiple subsystems?
Antenna Software
Solar Panels Structures & Thermal
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14. Further Modifications
How can we detect events from the fault tree?
Check appropriate sensors for anomalous readings
Cross-reference with Telemetry Dictionary
Single points of failure
A fault event such that the entire system may fail
Denoted by Y/N
Sensor
Subsystem
Minimum Value (Raw)
Maximum Value (Raw)
Average (Raw)
MAGX
ADCS
1320
1400
1343
MAGY
1468
1546
1486
MAGZ
1222
1293
1241
MAGREF
1317
1365
1333
SOLAR_CURRENT_XP
EPS
4009
1928
SOLAR_CURRENT_XM
658
3967
1944
SOLAR_CURRENT_YP
1156
4032
3993
SOLAR_CURRENT_YM
1943
3855
1981
SOLAR_CURRENT_ZP
433
3598
2926
SOLAR_CURRENT_ZM
369
3694
1931
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15. EPS Fault Tree
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16. Antenna Fault Tree
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17. Solar Panels Fault Tree
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18. Putting the FTA to Use Monitoring satellite status Diagnostic Tool
Useful for monitoring time-dependent events (i.e. battery charge)
Allows mission operators to foresee possible failures and act accordingly
Diagnostic Tool
If a failure event does occur, its causes may be identified through the FTA
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19. References & Acknowledgments
Stamatelatos, Michael, and William Vesely. Fault Tree Handbook with Aerospace Applications. NASA, Aug Web. 29 Mar <
Long, Allen R. Beauty and the Beast - Use and Abuse of the Fault Tree as a Tool. Tech. Fault-tree.net. Web. 29 Mar < tree.net/papers/long-beauty-and-beast.pdf>.
"Fault Tree Analysis (FTA, System Analysis) Basics." Reliability Engineering, Reliability Theory and Reliability Data Analysis and Modeling Resources for Reliability Engineers. Weibull.com. Web. 29 Mar
Thanks to Trevor Schlieper and Katie Brissenden for their contributions to the FTA.
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20. CDH Fault Tree
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21. HSCOM Fault Tree
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22. PCOM Fault Tree
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23. ADCS Fault Tree
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24. Structural/Thermal Fault Tree
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