Risk mitigation for the ELT segments phasing

Transcription

1 Risk mitigation for the ELT segments phasing R&D SEMINAR ANNE-LAURE CHEFFOT E U R O P EA N S O U T H E R N O B S E RVATO RY / A I X M A RSEILLE U N I V ERS I T Y 30/11/2017 1

2 Source:ESO 30/11/2017 2

3 Source:ESO 30/11/2017 3

4 Primary mirror segmentation Critical numbers 39 meters diameter 798 segments 1.4m corner to corner 4mm gap between segments Controlled in Tip/Tilt Piston And also > 7000 edge sensors > 7000 actuators 30/11/2017 PHD DAY 2017 LAM 4

5 Perfect telescope 30/11/2017 PHD DAY 2017 LAM 5

6 Not so perfect any more 100nm Peak to Valley 30/11/2017 PHD DAY 2017 LAM 6

7 200nm Peak to Valley 30/11/2017 PHD DAY 2017 LAM 7

8 800nm Peak to Valley 30/11/2017 PHD DAY 2017 LAM 8

9 Completely banana 1000nm Peak to Valley 30/11/2017 PHD DAY 2017 LAM 9

10 30/11/

11 N=number of segments σ = residual RMS phasing error Source: Isabelle Surdej 30/11/

12 Can you see something? 30/11/2017 PHD DAY 2017 LAM 12

13 Challenge 30/11/2017 PHD DAY 2017 LAM 13

14 Solution 30/11/2017 PHD DAY 2017 LAM 14

15 Look at it locally 30/11/2017 PHD DAY 2017 LAM 15

16 Look at it globally Zeus SH Michelson (Internal metrology) Curvature Pyramid Active Phasing Experiment ESO/VLT /11/2017 PHD DAY 2017 LAM 16

17 Overview Baseline for the ELT primary One phasing run on sky every two weeks using Shack-Hartmann Two freshly recoated segment re-installed on M1 per day Risks High sensitivity to registration error (consequence of high segmentation) Degradation of the phasing over 2 weeks Mitigation Pupil plan phasing sensor to mitigate registration error Monitor the phasing during observation Phasing of one segment after replacement during sunny hours 30/11/

18 Phasing Baseline: Keck approach Shack-Hartmann mask phasing sensor No phasing during observation: high performance Edge sensor Maintenance Source: Keck Source : Chanan et al 1997 Source : ESO 30/11/

19 Risk assessment Baseline Associated risk Baseline Associated risk One phasing run on sky every two weeks using Shack-Hartmann High sensitivity to registration error Degradation of the phasing Two freshly recoated segment re-installed on M1 per day Degradation of the phasing 30/11/

20 How to mitigate? 30/11/

21 High sensitivity to registration error Registra What? Pupil plane phasing sensor to mitigate registration error 30/11/

22 High sensitivity to registration error Registra What? Pupil plane phasing sensor to mitigate registration error 30/11/

23 Source: LAM Source: INAF-Arcetri Source: IAC High sensitivity to registration error Active Phasing Experiment ASM :Active Segmented Mirror (61 Segment) Curvature Turbulence generator Internal Metrology ASM Phase Contrast Curvature Pyramid Shack- Hartmann Pyramid Parabola Source :ESO Phase Contrast 30/11/

24 High sensitivity to registration error Phase contrast sensor ZErnike Unit Sensor (LAM) Monitoring phasing during observation Source: LAM Source: I.Surdej Thesis Source: I.Surdej Thesis 30/11/

25 Monitor the phasing during observations Phasing the ELT with Adaptive optics Control Experiment (PEACE), Investigate cross-performance with AO ZEUS wavelength scan to increase capture range? 30/11/

26 Monitor the phasing during observations Phasing the ELT with Adaptive optics Control Experiment (PEACE), Investigate cross-performance with AO ZEUS wavelength scan to increase capture range? On going refurbishment Metrology = Edge Sensor Addition to fit ELT baseline ELT Spider Adaptive Optics Segmentation 30/11/

27 Local phasing phasing gun 30/11/

28 Local phasing Two freshly recoated segment re-installed on M1 per day Edge sensor: no phasing while observing Reference lost Day time phasing of one segment after replacement (Phasing gun) Range +-200um Precision~10-20nm Source : ESO 30/11/

29 Multiwavelength Shearing Interferometer Source: BIAS 30/11/

30 Multiwavelength Shearing Interferometer Source: BIAS 30/11/

31 Multiwavelength Shearing Interferometer Source: BIAS 30/11/

32 ELT M1 facility 30/11/

33 ELT M1 facility + Phasing gun 30/11/

34 Multiwavelength Shearing Interferometer 30/11/

35 Multiwavelength Shearing Interferometer To be done: Repeatability Average of N measurements (dispersion) 30/11/

36 Conclusion On going & future work: PEACE refurbishment AO cross performance Zeus capture range increase -> wavelength scan Phasing gun Miniaturisation Dispersion characterisation 30/11/