1. Deutsches SOFIA Institut Universität Stuttgart Second Gyro System for the SOFIA Telescope J.F. Wagner Deutsches SOFIA Institut, Universität Stuttgart, Germany

2. Symposium Gyro Technology 20092 Deutsches SOFIA Institut Universität Stuttgart Wide Field Imager (WFI) Fine Field Imager (FFI) Focal Plane Imager (FPI) aircraft vibrations aero-acoustics controller commanded attitude actual attitude actuators structure and mechanics gyroscopes perturbations data fusion tracker correction Attitude Control: Inertial Stabilization + {

3. Symposium Gyro Technology 20093 Deutsches SOFIA Institut Universität Stuttgart SOFIA’s Fiber Optic Gyroscopes Optical sensor module Opto-electronic module Initial situation Telescope pointing budget allocated for gyro drift: 0.04 arcsec Very low noise requirement dominated gyro design → Optical fiber length 3.4 km → Mean coil diameter150 mm → Closed loop operation Performance:Angular increment< 0.001 arcsec Dynamic range> 10.3 °/s Bandwidth> 1 kHz Random walk0.0003 °/√h In-run bias stability0.003 °/h

4. Symposium Gyro Technology 20094 Deutsches SOFIA Institut Universität Stuttgart SOFIA’s Fiber Optic Gyroscopes

5. Symposium Gyro Technology 20095 Deutsches SOFIA Institut Universität Stuttgart Constant Performance Two data sets available over a period of 9 years Data show very constant low noise behaviour Calibration 1999/2003 Calibration 2008

6. Symposium Gyro Technology 20096 Deutsches SOFIA Institut Universität Stuttgart Spare part Repair Second Gyro System First possibility: Exchange of the gyro box Gyro Box 2 nd Gyro Box Nasmyth Tube ATCUTASCU Failure Gyro Box

7. Symposium Gyro Technology 20097 Deutsches SOFIA Institut Universität Stuttgart Failure Second Gyro System Second possibility: Parallel system (hot standby) Gyro Box 2 nd Gyro Box Nasmyth Tube ATCUTASCU 2 nd ATCU Gyro BoxATCU

8. Symposium Gyro Technology 20098 Deutsches SOFIA Institut Universität Stuttgart Second Gyro System Comparison: Advantages (+) / Disadvantages (–) / Neutral (0) Gyro Box Exchange Hot Standby Accuracy+– Cost–– Software modification0– ATCU failure– ++ “Save a mission”–++ Flexibility of schedule– +