# Presentation: 168871

## OMI OPERATIONSSTATUS

- Jacques Claas
- Instrument Operations Team
- KNMI
- The Netherlands

## Content of Presentation

- Folding Mirror Mechanism (FMM) anomaly
- Operations status and outlook

## FMM anomaly: purpose of FMM

- The FMM is a stepper motor. It is needed when performing calibration measurements

- Design drawing of the OMI optical bench

- FMM

## FMM anomaly: overview

- On **Feb 28****th** at 00:23:18 GMT OMI stopped generating science data due to a FMM anomaly.
- Investigation started immediately after the occurrence of the anomaly. Parties involved:- Instrument Operations Team- Industry (Dutch Space and TNO-TPD)- NASA / AURA Flight Operations TeamDecisions were formalized by means of Non-Conformance Review Boards.
- OMI resumed generating science data on **March 3****rd** (only earth and dark measurements, no calibration measurements).
- As part of the anomaly investigation 13 FMM tests were carried out in the period March 8th – May 17th.
- Although the FMM tests provided detailed information on the in-flight FMM behaviour, the FMM behaved nominally during all tests and no root cause could be found for the anomaly.
- On **June 12****th** OMI resumed full nominal operations generating earth science data as well as calibration data.

## FMM anomaly: operating the FMM

- For calibration measurements:- assume an unknown initial FMM  position.- move the FMM from this unknown  position to calibration position 0 by  commanding 85 steps.- in case the FMM bounces against  the endstop, indicated by a dark  status of the opto-coupler, move the  FMM 4 additional steps from position  4 to position 0.- when the calibration measurement is  finished, move the FMM to the nadir  position 79.
-  For nadir (earth) measurements: - not needed to move the FMM,   because the default position is the   nadir position.

## FMM anomaly: what went wrong?

- Till Feb 19th the FMM always bounced against the calibration endstop when moving to the calibration position.
- Between Feb 19th and Feb 28th the FMM not always bounced.
- On Feb 28th, when moving the FMM into calibration position for a LED calibration measurement, the opto-coupler status remained “dark” even after the 4 additional steps.
- Automatically a Fault Management procedure started, resulting in a transition to Idle mode which effectively stopped the generation of science data.
- As part of the Fault Management procedure, the FMM was moved to nadir position.

## FMM anomaly: telemetry analysis

- Telemetry analysis showed that the FMM, as part of the Fault Management procedure, was indeed moved to nadir position.
- This was confirmed when, after March 3rd, earth images became available again which showed that the optical path was not blocked by the FMM.

## FMM anomaly: testing the FMM

**Purpose of various tests:**
**Tests 1-3**:Find out if the FMM can be moved around its nadir position?
**Tests 4-5**:Find out if the redundant FMM coils can be used, also in combination with the nominal FMM coils (double drive torque!)
**Tests 6-8**:Find out if the FMM can be moved from the nadir position 79 to position 2 without loosing steps in between due to mechanical/electrical wear.
**Tests 9-10**:Find out if there is mechanical/electrical wear or opto-coupler problem at position 1.
**Tests 11 (without WLS) – 12 (with WLS)**:Find out if there is mechanical/electrical wear or opto-coupler problem at position 0; find out if bouncing is taking place.
**Test 13 (with WLS)**:Find out the precise position of the calibration endstop by commanding FMM to virtual position -4; find out when FMM jumps back.

## FMM anomaly: test results

- All tests were successful.
- During all tests the FMM showed nominal behaviour.
- There is no loss of steps when moving the FMM from nadir position to calibration position and vice versa.
- There is no indication for an opto-coupler problem.
- No bouncing against the calibration endstop takes place when commanding the FMM step-by-step.
- When using the WLS, the WLS signal is highest at FMM position 1 whereas position 0 (the calibration position) was expected.
- It turns out that the FMM position during a calibration measurement is just in front of the calibration endstop and not at the calibration endstop.
- A known initial position 79 can be assumed when starting to use the FMM.

## FMM anomaly: cause and corrective action

**Cause**:
- Despite all the successful tests, the root cause for the FMM anomaly has not been found.
- One possible cause (although it cannot be proven) is that, instead with the usual 4 steps, the FMM bounced 8 steps when moving to the calibration position. This has occurred only once during an on-ground test.
**Corrective action**:
- A relation is assumed between the changing bouncing behaviour as observed between Feb 19th and Feb 28th and the FMM anomaly on Feb 28th.
- By operating the FMM in a different way, bouncing against the calibration endstop can be avoided.
- All calibration measurements are performed by means of Stored Instruction Sequences (SISs). All SISs that use the FMM will be modified to avoid bouncing.
- In the next coming months old SISs will be replaced by new SISs.
- Replacing the old SISs by the new SISs will have no impact on the measurement schedule.
- The FMM is now continuously monitored by automated TM checking

## Operations Status and Outlook

- OMI performs nominal
- OMI is taking both earth and calibration measurements according to the (unchanged) Nominal Operations Baseline.
- On June 17th a new LED linearity measurement was performed for the first time giving more detailed information on the non-linear relation ship between the incoming flux on the CCD and the resulting number of electrons in the CCD read-out register.
- All calibration SISs that use the FMM will be updated to avoid bouncing of the FMM.
- 29 new orbit-type activities have been developed that enable a more flexible timing of the earth measurements during the ozone hole season. This is to avoid CCD saturation in the UV spectral region.
- Except for the FMM anomaly there have been no other instrument anomalies.
- OMI is thermally still very stable. No change of thermal settings needed.

## Slide 12

## Available 24/7

- KNMI

- Dutch Space

- Northrop Grumman

- Jacques Claas

- Mirna van Hoek

- Leo van Lent

- Ayman Mekhail

- AURA-FOT

- Joe Purcell

## Position calibration end-stop (result from FMM test #13)

## Ozone Hole 2006Aug 21 – Sep 9

- Ozone Hole 2006Aug 21 – Sep 9