The SiC hardware of the Sentinel-2 Multi Spectral Instrument

Transcription

1 The SiC hardware of the Sentinel-2 Multi Spectral Instrument ICSO 6c Telescopes and Large Optics Oral Session N 028 Michel BOUGOIN and Jérôme LAVENAC BOOSTEC michel.bougoin@mersen.com jerome.lavenac@mersen.com ICSO th International Conference on Space Optics, Ajaccio 1

2 SUMMARY 1. Boostec SiC material 2. Boostec SiC manufacturing technology 3. Experience in Space Telescopes 4. The Sentinel-2 Multi Spectral Instrument 5. The SiC hardware of the Sentinel-2 MSI 6. Conclusion ICSO th International Conference on Space Optics, Ajaccio 2

3 1. Boostec SiC material A Sintered Silicon Carbide (SSiC) For space optics, the key properties of Boostec SiC material are High specific stiffness ( 420 Gpa / 3.15 g/cm 3 ) High thermal stability (180 W.m/K / /K) Single SiC phase, highly homogeneous Microstructure and then physical properties perfectly isotropic (in particular the CTE) No mechanical fatigue No outgassing No degradation by space radiations Perfectly stable in time No moisture absorption, nor release Perfectly reproducible inside a part and from batch to batch no CTE mismatch measurable with accuracy in the range of ppm/k Physical properties kept or even enhanced down to cryo temperature qualified for Nirspec instrument to be operated at 30 K ICSO th International Conference on Space Optics, Ajaccio 3

4 1. Boostec SiC material Properties Typical 293 K Density 3.15 g/cm 3 Young s modulus 420 GPa Bending strength / Weibull modulus (coaxial double ring bending test) 400 MPa / 11 Toughness (K 1C ) 3.5 MPa.m 1/2 Coefficient of Thermal Expansion (CTE) /K Thermal Conductivity 180 W.m/K ICSO th International Conference on Space Optics, Ajaccio 4

5 1. Boostec SiC material The sintered SiC shows around 1 vol. % remaining porosity Closed (non inter connected) and Fine (typically Ф1 µm) Commonly masked with a pore free SiC CVD coating, when necessary, on the optical faces Thanks to its high purity, the CTE of Boostec SiC fits very well with the one of the ultra-pure CVD SiC ICSO th International Conference on Space Optics, Ajaccio 5

6 2. Boostec SiC manufacturing technology Manufacturing Monolithic Parts Near-net shaping large size and complex 3D shapes Cost-effective, reliable and quick process New size capability up to Φ 1.25m or 1.70mx1.20mx0.60m ICSO th International Conference on Space Optics, Ajaccio 6

7 2. Boostec SiC manufacturing technology Manufacturing 3m class parts with help of the Brazing Technique Starting from monolithic ground parts (previous slide) Giving highly stable assembly, cryo temperature Silicon + additives powder Molten silicon alloy SiC part N 1 SiC part N 2 Around 1500 C, the molten silicon alloy penetrates into the gap by capillary action. After cooling down, both parts are welded. SiC part N 1 SiC part N 2 ICSO th International Conference on Space Optics, Ajaccio 7

8 3. Our Experience in Space Telescopes 9 all Boostec SiC telescopes are now successfully operating in space 9 other Flight Models all Boostec SiC telescopes are being integrated or waiting for launch including ALADIN, NIRSPEC (JWST), GAIA ICSO th International Conference on Space Optics, Ajaccio 8

9 4. The Sentinel-2 Multi Spectral Instrument A major part of the GMES program 2 identical satellites and then 2 telescopes Embark the Multi-Spectral Instrument A large all-sic TMA designed by Astrium: M1,M2,M3, main structure and 2 focal planes hardware are made of SiC Will provide optical images in 13 spectral bands in the visible but also in the near infra-red A unique combination of 10 to 60m resolution and 290 km wide swath The MSI features Mass # 120 kg 1 st eigen frequency # 65 Hz Operational stability: angular 3 µrad, WFE 20 nm and defocus 3 µm ICSO th International Conference on Space Optics, Ajaccio 9

10 5. The SiC hardware of Sentinel-2 MSI The main structure of the MSI Holds the 3 SiC mirrors, the beam splitter device, the 2 focal planes and 3 stellar sensors Mounted on the satellite through 3 bolted bipods A lot of interfaces lapped down to 1µm flatness and accurately located 0.1 mm) Obtained by brazing the assembly of a large base-plate + M1 bracket + M3 bracket ICSO th International Conference on Space Optics, Ajaccio 10

11 5. The SiC hardware of Sentinel-2 MSI The main structure of the MSI Sized 1.47m x 0.93m x 0.62m Weighs only 44kg ICSO th International Conference on Space Optics, Ajaccio 11

12 5. The SiC hardware of Sentinel-2 MSI The MSI mirrors M2 M1 M3 M 1 M 2 Shape Mounting Size (mm) Weight (kg) Aspheric, of-axis, concave Central fixture at back side 442 x Aspheric, on-axis, convex Central fixture at back side 147 x M Aspheric, of-axis, concave Glued bipods on outer edges 556 x ICSO th International Conference on Space Optics, Ajaccio 12

13 5. The SiC hardware of Sentinel-2 MSI The MSI dichroïc beam splitter bracket The dichroïc splits the beam towards 2 focal planes 328mm x 212mm x 126mm kg ICSO th International Conference on Space Optics, Ajaccio 13

14 5. The SiC hardware of Sentinel-2 MSI The MSI focal planes The VNIR uses Si CMOS detectors (Op. T # 20 C) The SWIR uses HgCdTe ones which are individually mounted on small SiC packages (Op. T # - 80 C) All detectors are bolted on a SiC structure which also integrates a SiC radiator, thus allowing a passive cooling The detector area is lapped down to 1 µm flatness These both structures are fixed to the main telescope structure through 3 bipods SWIR detector support (5.4 kg) VNIR detector support (3.6 kg) ICSO th International Conference on Space Optics, Ajaccio 14

15 6. Conclusion 9 all Boostec SiC instruments are now successfully operating in space, including the Herschel Observatory which is the largest space telescope Astrium has now received all the SiC hardware of both Flight Models Sentinel-2 MSI, except the main structure of the 2 nd model which is at DRB level in Boostec The integration of the 1 st Flight Model is in good progress in Astrium Toulouse Sentinel-2 has again demonstrated that Boostec SiC material and technology allow making complex, large, innovative and highly stable parts or assemblies After Herschel and Gaia, the successful experience of Sentinel-2 shows that the pioneering time is behind us and that our SiC technology is fully mature and ready for the future large space scientific and earth observation missions ICSO th International Conference on Space Optics, Ajaccio 15

16 ESA ESTEC Sentinel-2 team and ASTRIUM one have put their trust in BOOSTEC team for carrying out the innovative Sentinel-2 MSI project; we greatly appreciated. We also express our warmest thanks to David Denaux (ASTRIUM) for his very constructive and fruitful collaboration on this project. Images courtesy of ASTRIUM and ESA Thank you for your attention ICSO th International Conference on Space Optics, Ajaccio 16