1. OSIRIS FDM Failure investigation summary
P. Kerhousse, ESA/ESTEC (TEC-MMM)
February 2004

2. Failure investigation summary
Contents
Failure description
Root causes tree
Failure analysis
Open issues
Identified risks
Recommendations
Issue date: 25th February 2005
Failure investigation summary

3. Failure investigation summary
Failure description (1/2)
What is the failure observed?
Failure identification:
Unexpected number of motor steps needed by the FDM mechanism to reach both the Open and Close positions given by the associated Open and Close micro-switches status.
Observables:
Number of steps commanded
Switches status
Camera pictures
Model:
ROSETTA-OSIRIS FDM NAC FM in orbit (20th January 2005)
Issue date: 25th February 2005
Failure investigation summary

4. Failure investigation summary
Failure description (2/2)
Is it the first failure occurrence?
Similar failures occurrence history:
WAC FDM QM during life testing
->Not treated as NCR/ MRB
WAC FDM FM during system acceptance testing
Only 1 g effect considered as possible root cause (jamming condition)
-> Manual assistance during closing
NAC FDM FM during system acceptance testing
Only 1g effect considered as root cause (jamming condition)
ROSETTA Satellite in-orbit commissioning (5th Sept 2004)
Software switch search logic considered as root cause
-> Change of FDM software
Issue date: 25th February 2005
Failure investigation summary

5. Failure investigation summary
Root causes tree (1/2)
What can explain the failure observed?
(A) Motor steps commands missed
(1) MCB failure
(2) DC/DC converter failure
(3) Low level S/W failure
(4) High level S/W failure
(5) Harness failure
(B) Motor steps loss
(1) Motor failure
(2) Increase of resistive torque
(3) Dynamic coupling
(4) End stop reached
Issue date: 25th February 2005
Failure investigation summary

6. Failure investigation summary
Root causes tree (2/2)
What can explain the failure observed?
(C) Wrong switch status
(1) MCB failure
(2) Switch failure
(3) Switch fixation failure
(4) Harness failure
(D) Mechanical position inaccuracy
(1) Mechanism backlash
(2) Switches reproducibility
(3) External torque variations
Issue date: 25th February 2005
Failure investigation summary

7. Failure investigation summary
Failure analysis (1/2)
Issue date: 25th February 2005
Failure investigation summary

8. Failure investigation summary
Failure analysis (2/2)
Issue date: 25th February 2005
Failure investigation summary

9. Failure investigation summary
Open issues (1/2)
End stop not reached: How to explain?
Open switch
release is located above the activation
activation and release are sliding in the Open direction
Close switch
activation is sliding in the Close direction
Release is sliding in the Open direction
The Open to Close switches distance is increasing (more pronounced on activation than on release)
Issue date: 25th February 2005
Failure investigation summary

10. Failure investigation summary
Open issues (2/2)
End stop reached: How to explain?
Open switch
activation and release are slightly sliding in the Open direction
Close switch
activation is sliding in the Close direction
Release position is stable
The Open to Close switches distance is increasing (by far more pronounced on activation than on release)
Issue date: 25th February 2005
Failure investigation summary