1 of 28 A design study of a Cryogenic High Accurate Derotator.

2 of 28 A design study of a Cryogenic High Accurate Derotator. Assignment Perform a design study a derotator to prevent the smearing of the image with such a precision that an object falling on one pixel does not shift more then 1/5 th (6.2μm) in one hour of observation time.

3 of 28 Introduction (E-ELT,METIS) Problem definition Concept design Feasibility test Conclusion and remarks A design study of a Cryogenic High Accurate Derotator.

4 of 28 A design study of a Cryogenic High Accurate Derotator. Introduction (E-ELT,METIS)

5 of 28 A design study of a Cryogenic High Accurate Derotator. Mid-infrared E-ELT Imager and spectrograph Imaging/spectroscopy in the mid infrared range (wavelengths of µm) Environment cryogenic and vacuum Introduction (E-ELT,METIS)

6 of 28 A design study of a Cryogenic High Accurate Derotator. Mid-infrared E-ELT Imager and spectrograph Imaging/spectroscopy in the mid infrared range (wavelengths of µm) Environment cryogenic and vacuum Introduction (E-ELT,METIS)

7 of 28 A design study of a Cryogenic High Accurate Derotator. Why is derotation necessary The detector of the metis instrument needs and integration time of at least 15 minutes to get an high enough signal to noise ratio. When not derotating smearing on the detector will occur, due to the rotation of the earth. Because of the altitude azimuth configuration of the E-ELT the rotation can not be compensated by the telescope

8 of 28 A design study of a Cryogenic High Accurate Derotator. Optical configuration Angle (α mir )≈28 degrees Length (L mir )= mm Length science beam (B mir )=195 mm Radius of the science beam (R mir )≈58.0 mm Height of the second mirror (H mir )≈161.7 mm

9 of 28 A design study of a Cryogenic High Accurate Derotator. Influence of DOF Mirror influences 6 degrees of freedom for each mirror Only 3 influence the science beam Derotator 6 degrees of freedom for the derotator 4 influence the science beam

10 of 28 A design study of a Cryogenic High Accurate Derotator. Influence of DOF Mirror influences 6 degrees of freedom for each mirror Only 3 influence the science beam Derotator 6 degrees of freedom for the derotator 4 influence the science beam Movement in x-direction Rotation around x-axis(α x ) Movement in y-direction Rotation around y-axis(β Y ) Movement in z-direction Rotation around z-axis(γ Z )

11 of 28 A design study of a Cryogenic High Accurate Derotator. Influence of DOF Derotator Specific property when rotating around the specific rotation point Red (1 degree) Blue (2 degrees) Rotation around y-axis(β Y )

12 of 28 A design study of a Cryogenic High Accurate Derotator. Concluding optical analysis When defining the rotation point as shown in the previous slide the problem will reduce to a 3 DOF problem. In the x-z plane the axis of the derotator needs to be directed to the rotation point (β) The angle of the axis of the derotator in the z- y plane needs to be zero (α). The rotation around the axis needs to be controlled to control the rate of derotation (γ)

13 of 28 A design study of a Cryogenic High Accurate Derotator. Problem definition The end goal for the derotator is to prevent the smearing of the image with such a precision that an object falling on one pixel does not shift more then 1/5 th (6.2μm) in one hour of observation time.

14 of 28 A design study of a Cryogenic High Accurate Derotator. Requirements mirrors Rotation: 2,6 arcsecond Translation: 5 micrometer Environmental aspects Working temperature: K Working pressure bar

15 of 28 A design study of a Cryogenic High Accurate Derotator. Requirements Derotator Requirements derotator rotation α and β: 2,6 arcseconds rotation γ: 2 arcseconds Maximum rotation speed: 7,5 degrees/hour Minimum rotation speed: 0 degrees/hour Setup speed: 90 degrees/minute Needs to rotate in both directions MTBF: hours Maximum allowed weight: 30 Kg Environmental aspects Working temperature: K Working pressure bar

16 of 28 A design study of a Cryogenic High Accurate Derotator. Concept design Derotator

17 of 28 A design study of a Cryogenic High Accurate Derotator. Concept design Derotator

18 of 28 A design study of a Cryogenic High Accurate Derotator. Concept design Derotator

19 of 28 A design study of a Cryogenic High Accurate Derotator. Feasibility test Purpose of test setup Test the feasibility of the used principles Test the accuracy of the capacitive sensors Kept as simple as possible Modelled as a pendulum

20 of 28 A design study of a Cryogenic High Accurate Derotator. Feasibility test Calculating PID values Controller variableValue KpKp 2000 KiKi 1000 KdKd 200

21 of 28 A design study of a Cryogenic High Accurate Derotator. Feasibility test Closed loop bode plot Phase margin in zero degrees up to 1 hertz

22 of 28 A design study of a Cryogenic High Accurate Derotator. Feasibility test

23 of 28 A design study of a Cryogenic High Accurate Derotator. Feasibility test

24 of 28 A design study of a Cryogenic High Accurate Derotator. Test results Required accuracy: 2,6 arcseconds = 12 micro radians Signal that needs to be followed is of very low frequency Applying a sinusoidal reference signal with: Amplitude 400 micro radians Frequency 0,02 Hz

25 of 28 A design study of a Cryogenic High Accurate Derotator. Test results Proven that an accuracy of 2,6 arcsecond is feasibly with a low disturbing frequency (up to 0.02 Hz) This was done with relative simple building block (capacitive sensor; Voice coil actuator)

26 of 28 A design study of a Cryogenic High Accurate Derotator. Conclusion and remarks With optical analyses the 4 DOF system is reduced to a 2 DOF system This 2 DOF can steer the science beam on the detector Errors in the mirrors position can be compensated with the derotator reducing the requirements on the mirror Relative easy to build a system with a 2,6 arcsecond angular accuracy at low frequencies

27 of 28 A design study of a Cryogenic High Accurate Derotator. Conclusion and remarks There is still some work that needs to be done The test setup can be improved with a discrete controller such that error at higher frequencies is reduced A trade of has to be made between the amount of heat dissipation and the required force to reduce error at higher frequencies A thermal analyses of the system needs to be done

28 of 28 A design study of a Cryogenic High Accurate Derotator. Questions