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Cleanliness and Calibration stability of UV instruments on SOHO

Explore efforts in maintaining cleanliness and calibration stability of UV instruments on SOHO, outlining results and implications for future solar missions. Learn about preventive measures and design rules for calibration degradation.

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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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