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Optical Probe Experiment (OPE)

NSSDC ID: 1985-056A-09
Mission Name: Giotto
Principal Investigator: Dr. A. C. Levasseur-Regourd


The optical probe technique is employed in this investigation to determine, unequivocally, changes in the densities of emissive gases (OH, C2, CN, CO+, and CS) and scattering dust, as well as to measure the optical properties of dust, in the coma of Halley's comet. The instrument contains no moving parts and performs photopolarimetric measurements parallel to the direction of motion through the coma. The choice of wavelengths is the following: 368, 444, 575, and 718 nm for dust, and 307, 387, 462, and 514 nm for gases. The rapid motion of the spacecraft allows line-of-sight measurements to be differenced so that the resulting brightnesses and polarizations refer to the small volume of space of about 140 km length centered at the moving probe.

Alternate Names

  • HOPE
  • OPE
  • Halley Optical Probe Experiment (HOPE)

Facts in Brief

Mass: 1.32 kg
Power (avg): 1.2 W
Bit rate (avg): 0.723 bps

Funding Agencies

  • Centre National de la Recherche Scientifique (France)
  • NASA-Office of Space Science (United States)


  • Planetary Science: Small Bodies

Additional Information

Questions or comments about this experiment can be directed to: Dr. David R. Williams.



NameRoleOriginal AffiliationE-mail
Dr. Jerry L. WeinbergCo-InvestigatorUniversity of
Dr. Phillipe L. LamyCo-InvestigatorCNRS, Laboratoire d'Astronomie Spatiale 
Dr. A. C. Levasseur-RegourdGeneral ContactCNRS, Service d'Aeronomie 

Selected References

Levasseur-Regourd, A. C., et al., The Giotto optical probe experiment, In--The Giotto Mission--Its Scientific Investigations, ESA SP-1077, edited by R. Reinhard and B. Battrick, pp. 187-193, Mar. 1986.

Levasseur-Regourd, A. C., et al., Optical probing of comet Halley from the Giotto spacecraft, Nature, 321, No. 6067, 341-344, May 1986.

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