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Session 6 Special Test Design of the cryo-optical test of the PLANCK reflectors

Session 6 Special Test Design of the cryo-optical test of the PLANCK reflectors (S. Roose (CSL), A. Cucchiaro (CSL), & D. de Chambure (ESTEC)) Speaker:S. Roose (Centre Spatial de Liège). Introduction: the test objectives

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Session 6 Special Test Design of the cryo-optical test of the PLANCK reflectors

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  1. Session 6 Special Test Design of the cryo-optical test of the PLANCK reflectors (S. Roose (CSL), A. Cucchiaro (CSL), & D. de Chambure (ESTEC)) Speaker:S. Roose (Centre Spatial de Liège) Torino 18/19 March 2003

  2. Introduction: the test objectives • PLANCK reflectors: 2 CFRP off -axis ellipsoids to be tested separately (SR: 1050 mm x 1100 mm) (PR:1550 mm x 1890 mm) • measure the surface figure error (SFE) difference between 293K and 40K • measure the focus displacement between 293K and 40K Torino 18/19 March 2003 Speaker: S.Roose

  3. Surface figure error measurement: the challenges • relative SFE measurement method with a resolution of about 1 m (small deformations) on a SFE characterised by high SFE slopes (1 mrad) • relative focus displacement measurement with 20 m accuracy (PR inter-focal distance: 21 m) Torino 18/19 March 2003 Speaker:S. Roose

  4. ...the challenges (cont’d) • proposed method wavefront measurement method in stigmatic configuration (single pass for SR, double pass for PR) Torino 18/19 March 2003 Speaker:S. Roose

  5. Infrared interferometry • SFE is hidden in the wave-front measured by the interferometer • operational wavelength:10.6 m • WFE resolution < 1 m • high wave-front sampling rate (detector resolution): 320 x 240 • increased resolution possible with sub-aperture stitching • wave-front slope limitation: l wavelength per 4 pixels • slope limitation translated at reflector level (SFE slopes): 0.1 mrad (PR), 0.2 mrad (SR). • in principle incompatible with predicted slopes, but... Torino 18/19 March 2003 Speaker:S. Roose

  6. Infrared interferometry (cont.d) • simulation of interferogram recording and processing • secondary reflector at 40 K (worst case) • use of a standard interferometer with sub-aperture stitching Torino 18/19 March 2003 Speaker:S. Roose

  7. Infrared interferometry (cont.d) • primary reflector at 40 K (worst case) • need of high resolution interferometer (800 by 800 pixels) • IR interferometer (1200 by 1200 pixels) under development Torino 18/19 March 2003 Speaker:S. Roose

  8. Hartmann test (back-up solution) • wave-front slope measurement method • dynamic range scalable (at the price of sampling rate) • centroid precision 0.1 pixel • dynamic range of 10 pixel • campling rate: 20 • incompatible with specs. Torino 18/19 March 2003 Speaker:S. Roose

  9. Hartmann test (cont’d) PR-SFE reconstructed with 100 by 100 samples SR-SFE reconstructed with 64 by 64 samples • commercial instrument not available • new concept: high sampling rate with dynamic Hartmann test Torino 18/19 March 2003 Speaker:S. Roose

  10. Secondary reflector test configuration Torino 18/19 March 2003 Speaker:S. Roose

  11. Secondary reflector test configuration (cont’d) • interferometer camera and laser outside vacuum chamber • interferometric cavity on 5 DOF outside thermal shrouds • illumination optics mounted on 3 DOF outside thermal shrouds • metrology for focus search: • 1) LVDT to measure PR I/F wrt CSL I/F (<10 m) • 2) T° regulation of optical bench and supports (<0.2 K) • (<5 m) • 3) stigmatic image (minimize WFE):(<2 m) Torino 18/19 March 2003 Speaker:S. Roose

  12. Primary reflector test configuration Torino 18/19 March 2003 Speaker:S. Roose

  13. Primary reflector test configuration (cont’d) • interferometer camera and laser outside vacuum chamber • interferometric cavity on 5 DOF outside thermal shrouds • convex spherical mirror (Diameter 1500 mm): inside shrouds mounted 3 DOF • metrology for focus search: • 1) LVDTs to measure PR I/F wrt CSL I/F (<10 m) • 2) T° regulation of optical bench and supports (<0.2 K) • (<5 m) • 3) stigmatic image (minimize WFE):(<2 m) • 4) in situ radius measurement of contraction of spherical mirror: (<0.1 ppm) ) or (<3 m) Torino 18/19 March 2003 Speaker:S. Roose

  14. Reflector cool-down • Radiative cooling • Thermal control of conductive I/F (0 Watt) • Permanent losses via optical apertures Torino 18/19 March 2003 Speaker:S. Roose

  15. Conclusions • SR test foreseen in FOCAL 3 facility, July 2003 • PR test foreseen in upgraded FOCAL X facility, december 2003 • Challenges: • Manufacturing of convex spherical mirror • Manufacturing of high resolution IR interferometer Torino 18/19 March 2003 Speaker:S. Roose

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