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Fifth European Conference on Space Debris

30 March - 2 April 2009
ESA/ESOC
Darmstadt, Germany


Preliminary Results from Spectroscopic Observations of Space Debris

T. Schildknecht, A. Vananti (Astronomical Institute, University of Bern, Switzerland)
H. Krag (ESA / ESOC, Darmstadt, Germany)
Ch. Erd (ESA / ESTEC, Noordwijk, Netherlands)

Paper Presented at the 5th European Space Debris Conference,
Darmstadt Germany, March 30 - April 2 2009


Objectives

  • Acquire First Experience with Reflection Spectroscopy at the OGS
    • Spectrograph at OGS never used for fast moving targets
      • Experiment
  • Get First Spectra of Space Debris at High Altitudes
    • Ultimate goal are spectra of high area-to-mass ratio GEO-like objects
      • material
    • Start with bright, known objects
      • Use known surface material for calibrationd
    • Try fainter debris

Major Observational Challenges

  • Reflection spectroscopy
    • quantitative comparison of the measured spectrum with the spectrum of the illuminating source
    • careful calibration of extinction
  • Tracking
    • first acquisition of satellites/debris
      • often outside field of view of 13 arcm(combination of mount model and ephemeris errors)
    • autoguiding not possible for satellites/debris objects
      • most objects remain in 5-slit for < 4 minutes
  • Faint Objects
    • Very low signal-to-noise
    • observations have experimental character and are very time consuming

Dismounting the Space Debris Camera

Mounting the ESA OGS Spectrograph

Spectrograph

  • Low resolution spectrograph
  • The OGS ESA spectrograph uses grisms as dispersive elements
  • Filters needed to separate second order spectra

Grisms

  • Available grisms

    • lowest dispersion selected (GrismBB):
      • best S/N for given magnitude and integration time
      • wavelength: 450 -950 nm
      • dispersion: 0.4 nm/pixels

    Selection of Objects

    • Four types
      • minor planets (results to be compared with published data)
      • large intact GEO objects (catalogue objects)
      • bright GEO debris objects
      • bright high AMR GEO objects
    • Selection criteria
      • orbit quality
      • availability of manufacturer data on surface materials
      • brightness
      • visibility constraints (phase angle, Earth shadow, Milky Way, etc.

    Observed Objects (Feb 2009)

    2nd Order Spectra

    Extinction

    Air mass
    1.02
    1.13
    1.4
    1.94

    Extinction coefficients

    Response Function

    Solar analog:
    • Implicit response function
    • Solar spectrum
    MSG-2 raw
     
    Normalize Spectrum
    • raw/solar analogue (extinction!)

    Phase Angle Dependence

    Meteosat MSG 2 at different phase angles:
    • 38
    • 60
    • 88

    Spectrum as a Fingerprint?

    Object S92005
    • GTO debris
    • Magnitude 14
    • AMR 0.02
    • two nights
    Assumptions:
    • attitude?
    • same phase angle
    Features:
    • slope
    • modulation
    • shape
    • peaks

    Solar Cells?

    Minor Planets vs. Debris

    Debris:
    • S92005 GEO
    • E08211A GEO
    Planets:
    • Nausikaa
    • Pomona
    Influence of space environment on debris => reddening ?

    Conclusion

    • It works!
    • First spectra of space debris in GEO and GTO
    • Spectra of the same object are consistent
    • Debris show different characteristics
    • The features might be used to identify objects
    • Observations seem to confirm the reddening effect
    • Still a long way until we can identify the materials of the high area-to mass objects

    6 2009


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