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Cleanliness and Calibration stability of UV instruments on SOHO

Cleanliness and Calibration stability of UV instruments on SOHO. (Dedicated to Philippe Lemaire) By Udo Schühle Max-Planck-Intitut für Sonnensystemforschung 37191 Katlenburg-Lindau, Germany. Outline of the talk. Conclusions Cleanliness efforts for SOHO UV instruments

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Cleanliness and Calibration stability of UV instruments on SOHO

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  1. Cleanliness and Calibration stability of UV instruments on SOHO (Dedicated to Philippe Lemaire) By Udo Schühle Max-Planck-Intitut für Sonnensystemforschung 37191 Katlenburg-Lindau, Germany P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  2. Outline of the talk • Conclusions • Cleanliness efforts for SOHO UV instruments • Calibration stability of SOHO UV instruments: some results • Relevance for future solar missions P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  3. Conclusions • SOHO UV instruments have been very stable due to the successful cleanliness program. but • SOHO UV detectors have been remarkably unstable. P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  4. Instruments on SOHO Ultraviolet remote sensing telescopes and spectrographs: CDS EIT SUMER UVCS Remote sensing Instrumentation: • CDS (Coronal Diagnostics Spectrometer) • EIT (Extreme ultraviolet Imaging Telescope) • SUMER (Solar Ultraviolet Measurements of Emitted Radiation) • SWAN (Solar Wind Anisotropies) • UVCS (Ultraviolet Coronagraph Spectrometer) • LASCO (Large Angle and Spectrometric Coronagraph) Helioseismology Instrumentation: • MDI/SOI (Michelson Doppler Imager/Solar Oscillations Investigation) • GOLF (Global Oscillations at Low Frequencies) • VIRGO (Variability of Solar Irradiance and Gravity Oscillations) In-situ instrumentation: • CELIAS (Charge, Element, and Isotope Analysis System) • COSTEP (Comprehensive Suprathermal and Energetic Particle Analyzer) • ERNE (Energetic and Relativistic Nuclei and Electron experiment) P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  5. Degradation of solar UV space instruments: OSO 8 P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  6. Degradation of solar UV space instruments: UARS-SUSIM Optical path degradation of SUSIM during 2.5 years of the UARS mission P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  7. Stability of calibration: concerns • Molecular contamination - From outgassing organic materials - From ground facilities and test environment • Polymerisation of organic contaminants by solar UV (especially on mirrors of solar instruments)  Degradation of responsivity • Laboratory and space experiments have quantitatively measured the UV-degradation. P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  8. Calibration degradation: preventive measures (1) • Establishment of SOHO Cleanliness Review Board and SOHO Intercalibration Working Group • SOHO Cleanliness Control Plan • Instrument Cleanliness Control Plans P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  9. Calibration degradation: preventive measures (2) • Most important preventive measures: • Determine your contamination sensitivity • Design your instrument for cleanliness: Design features, material selection • Avoid contamination during ground handling P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  10. Cleanliness design rules(derived for SUMER) • Material selection: metal optical housing (no organic composite material) • Avoid organic material inside optical housing (to minimise potential outgassing) • Aperture door to close/open the optical compartment (to reduce ingress from outside) • Solar wind deflector plates (with HV applied to deflect solar wind away from the telescope mirror) • Use of ultra-high vacuum components/materials inside optical housing (high-T materials) • Keep electronic components outside optical housing (to keep organic materials outside) • Large venting ports for all subsections of the optical housing (for efficient venting) • Purging of optical compartments at all times (to overpressurise and clean away offgassing species) • Keep primary mirror at highest temperature by solar illumination (to reduce deposition on sensitive surfaces) • Dry lubrication on MoS2 basis for all mechanisms (inorganic lubrication, no outgassing) • Use flexural metal pivots instead of bearings where possible (no lubrication needed) P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  11. Calibration stability, In-flight calibration Laboratory calibration by secondary source standards traceable to a primary standard. In-flight calibration tracking by observing a constant source: - the “quiet Sun” - celestial standards (stars) - calibration lamps (not for SOHO) - Calibration updates by rocket “underflight” P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  12. Calibration stability of SOHO instruments (example: SUMER) P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  13. Calibration stability of SOHO instruments (example: SUMER) P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  14. How much science can you make with a photon?(An excursion) • SUMER total accumulated counts: 1012 (during 108 s) • # of photons per publication: 2x109 For comparison: • # of 10eV-photons in one laser pulse of 1 mJ: 1015 • This is a typical laser pulse delivered in 10-8 s!  SUMER is extremely „photo-science-efficient“ P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  15. CDS burn-in of NIS detector at 58.4 nm P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  16. Example EIT: 304Å response vs. time P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  17. Intercalibration of SUMER and CDS He I 58.4 nm CDS SUMER Mg X 62.4 nm Mg X 60.9 nm P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  18. Calibration stability: Effect of SOHO accidental loss of attitude • 30% loss of sensitivity • Result of thermal cycling! • Redistribution of contaminants P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  19. Relevance for future solar missions • SOHO has extremely stable orbit: • Always Sun pointing • No eclipses • No (almost) changes to the orbit • Thermal stability • Future missions might not have such stable conditions (e.g. SDO, Solar Orbiter) • Redistribution of contaminants, temperature sensitivity P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  20. Lessons learned from SOHO • Calibration tracking throughout a mission is very difficult. Thus, recalibration, Intercalibration among instruments and calibration underflights are necessary • The cleanliness efforts have been necessary and were not excessive • Cleanliness design (at spacecraft and instrument level) greatly reduces contamination P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

  21. Literature • For further information read the book: “The Radiometric Calibration of SOHO“, ISSI Scientific Report SR-002, in press, 2002, (eds. A. Pauluhn, M.C.E. Huber, and R. v. Steiger) P. Lemaire’s retirement seminar Orsay, 18./19. Nov. 2004

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