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

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

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

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

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

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

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

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

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

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