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Three-dimensional Positive Ion Analyser (JPA)

NSSDC ID: 1985-056A-05
Mission Name: Giotto
Principal Investigator: Dr. Alan D. Johnstone


The objective of this investigation is to measure the plasma flow around Comet Halley in order to study (1) the mass loading of the solar wind by ions of cometary origin, (2) the existence, location, and strength of the upstream shock transition in the solar wind flow, (3) the position of and forces controlling the pressure balance surface between the cometary and the solar plasma, (4) the processes that form tail rays and other discrete visible features in the coma, and (5) the detection of wave motion induced by the cometary interaction that leads to the thermalization of solar wind and implanted ions. The instrument employs two sensors. One is a 270-deg spherical electrostatic energy analyzer (EEA) with a microchannel plate detector that measures the three-dimensional energy/charge distribution of positive ions from 10 eV to 20 keV over the polar angle range 20 - 180 deg with respect to the spin axis of the spacecraft. A complete set of measurements is obtained every spin period (4 s). The second sensor consists of a quadrispherical EEA with six time-of-flight analyzers set at different polar angles in the range 20 - 160 deg. The three-dimensional energy distribution of five major mass groups of ions up to 44 u over the energy range 0.1 - 70 keV is measured in 32 spin periods (128 s).

Alternate Names

  • JPA

Facts in Brief

Mass: 4.7 kg
Power (avg): 4.4 W
Bit rate (avg): 1.355 bps

Funding Agencies

  • Consiglio Nazionale delle Richerche, Italy (Italy)
  • Max-Planck-Institut (Federal Republic of Germany)


  • Planetary Science: Small Bodies

Additional Information

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



NameRoleOriginal AffiliationE-mail
Prof. Reimar LuestCo-InvestigatorEuropean Space Agency 
Dr. Helmut R. RosenbauerCo-InvestigatorMax-Planck-Institut fur
Dr. P. Ricardo CerulliCo-InvestigatorCNR, Space Plasma
Prof. Ludwig F. B. BiermannCo-InvestigatorMax-Planck-Institut fur Extraterrestrische Physik 
Dr. Goetz PaschmannCo-InvestigatorMax-Planck-Institut fur Extraterrestrische
Dr. Gerhard HaerendelCo-InvestigatorMax-Planck-Institut fur Extraterrestrische
Dr. Vittorio FormisanoCo-InvestigatorCNR, Space Plasma
Dr. Max K. WallisCo-InvestigatorUniversity College,
Prof. Marino DobrowolnyCo-InvestigatorCNR, Space Plasma
Dr. Roberto TerenziCo-InvestigatorCNR, Space Plasma
Dr. Duncan A. BryantCo-InvestigatorRutherford Appleton
Dr. Klaus JockersCo-InvestigatorMax-Planck-Institut fur
Mr. Denison R. LepineCo-InvestigatorRutherford Appleton
Dr. J. David WinninghamCo-InvestigatorSouthwest Research
Dr. Wolfgang StudemannCo-InvestigatorMax-Planck-Institut fur Aeronomie 
Dr. William C. FeldmanCo-InvestigatorLos Alamos National
Prof. Alberto EgidiCo-InvestigatorCNR, Space Plasma
Prof. Henri RemeCo-InvestigatorCNRS Centre d'Etudes Spatiale des
Dr. Alan D. JohnstoneGeneral ContactMullard Space Science Laboratory 
Dr. Berend WilkenCo-InvestigatorMax-Planck-Institut fur Aeronomie 
Dr. Hermann Ulrich SchmidtCo-InvestigatorMax-Planck-Institut fur Physik und

Selected References

Glassmeier, K.-H., et al., Spectral characteristics of low-frequency plasma turbulence upstream of comet P/Halley, J. Geophys. Res., 94, No. A1, 37-48, Jan. 1989.

Coates, A. J., et al., Plasma parameters near the comet Halley bow shock, J. Geophys. Res., 95, No. A12, 20701-20716, Dec. 1990.

Johnstone, A. D., et al., The Giotto three-dimensional positive ion analyser, In--The Giotto Mission--Its Scientific Investigations, ESA SP-1077, edited by R. Reinhard and B. Battrick, pp. 15-32, Mar. 1986.

Huddleston, D. E., and A. D. Johnstone, Relationship between wave energy and free energy from pickup ions in the comet Halley environment, J. Geophys. Res., 97, No. A8, 12217-12230, Aug. 1992.

Johnstone, A., et al., Ion flow at comet Halley, Nature, 321, No. 6067, 344-346, May 1986.

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