Deutsches SOFIA Institut

Universität Stuttgart

Second Gyro Systemfor the SOFIA Telescope

J.F. Wagner

Deutsches SOFIA Institut, Universität Stuttgart, Germany

Symposium Gyro Technology 2009 2

Deutsches SOFIA Institut

Universität Stuttgart

• Wide Field Imager (WFI)• Fine Field Imager (FFI)• Focal Plane Imager (FPI)

aircraft vibrations aero-acoustics

controller

commandedattitude

actualattitude

actuatorsstructure and mechanics

gyroscopes

perturbations

data fusion

tracker correction

Attitude Control: Inertial Stabilization

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Symposium Gyro Technology 2009 3

Deutsches SOFIA Institut

Universität Stuttgart

SOFIA’s Fiber Optic Gyroscopes

Optical sensor module

Opto-electronicmodule

Initial situation

• Telescope pointing budget allocatedfor gyro drift: 0.04 arcsec

• Very low noise requirementdominated gyro design

→ Optical fiber length 3.4 km→ Mean coil diameter 150 mm→ Closed loop operation

Performance: Angular increment < 0.001 arcsecDynamic range > 10.3 °/sBandwidth > 1 kHzRandom walk 0.0003 °/√hIn-run bias stability 0.003 °/h

Symposium Gyro Technology 2009 4

Deutsches SOFIA Institut

Universität Stuttgart

SOFIA’s Fiber Optic Gyroscopes

Symposium Gyro Technology 2009 5

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

Symposium Gyro Technology 2009 6

Deutsches SOFIA Institut

Universität Stuttgart

Spare partRepair

Second Gyro System

First possibility: Exchange of the gyro box

Gyro Box

2nd

Gyro Box

NasmythTube

ATCU TASCU

Failure

Gyro Box

Symposium Gyro Technology 2009 7

Deutsches SOFIA Institut

Universität Stuttgart

Failure

Second Gyro System

Second possibility: Parallel system (hot standby)

Gyro Box

2nd

GyroBox

NasmythTube

ATCU TASCU

2nd

ATCU

Gyro Box ATCU

Symposium Gyro Technology 2009 8

Deutsches SOFIA Institut

Universität Stuttgart

Second Gyro System

Comparison: Advantages (+) / Disadvantages (–) / Neutral (0)

Gyro Box Exchange Hot Standby

Accuracy + –

Cost – – –

Software modification 0 –

ATCU failure – – ++

“Save a mission” – ++

Flexibility of schedule – – +