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Ion Mass Spectrometer (IMS)

NSSDC ID: 1985-056A-03
Mission Name: Giotto
Principal Investigator: Prof. Hans R. Balsiger


The objective of the investigation is to measure the ion composition, energy, and angular distribution in the coma of Comet Halley. The instrument consists of two sensors: the High-Energy Range Spectrometer (HERS) specialized for the outer coma and the High-Intensity Spectrometer (HIS) specialized for the inner coma. The HERS sensor has (1) an electrostatic mirror for deflecting ions from the spacecraft ram direction into the sensor, instead of having the solar wind ions enter; (2) cylindrical acceleration grids which change the energy of the ions so they can pass through the magnetic analyzer; (3) a sector magnet that acts as a momentum/charge filter; (4) an electrostatic deflection plate that sorts the ions by energy/charge; and (5) particle detectors consisting of a two-dimensional microchannel plate (MCP) and channel-electron-multipliers (CEM) for measuring mass/charge and elevation angle. The energy range is from 20 eV to nearly 16 keV, depending on the M/Q, and the mass is determined in 3 or 4 mass groups (e.g., 1 to 4, 4 to 16, 16 to 64 u) with a mass resolution of M/delta M equal to about 20. The elevation angle, the polar angle relative to the spin axis, covers 30 deg and is measured in 4 bins, giving a resolution of 7.5 deg. The azimuth angle is spin-scanned and has a resolution of 4 deg. The MCP allows the simultaneous measurement of mass and elevation angle for a given ion momentum per charge (8 kV). A complete scan over mass, energy, and angle takes about 12 s, but other scans can be selected. The HIS sensor is used to measure the relatively cold, low-energy cometary species. This sensor has (1) a set of deflection plates above the spacecraft skin; (2) a quadrispherical lens followed by (3) a set of acceleration grids; (4) a permanent magnet; (5) a second quadrispherical lens, or analyzer; (6) a block of glass with conductive surfaces with holes in four directions that serves as a particle distributor and amplifier; and (7) 16 CEMs to detect the emergent particles. HIS measures energies from 300 to 1625 eV over a M/Q of 12 - 65 with a resolution (M/Delta M) of about 20, in an elevation angular range of 27 deg. The azimuth angle is spin-scanned and the time resolution for a set of measurements is about 4 s. The density range covered by HERS is 1.E-3 to 1.E2/cc, while that for HIS is 1.E-2 to 1.E4/cc. The instrument uses a microprocessor for operation and control. More details about this instrument can be found in "The Giotto Mass Spectrometer" by Balsiger et al., ESA SP-169, June 1981.

Alternate Names

  • IMS

Facts in Brief

Mass: 9.0 kg
Power (avg): 6.3 W
Bit rate (avg): 3.253 bps

Funding Agency

  • 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. Alan J. LazarusCo-InvestigatorMassachusetts Institute of
Dr. Richard D. SharpCo-InvestigatorLockheed Palo Alto 
Dr. Wesley T. Huntress, Jr.Co-InvestigatorNASA Jet Propulsion
Dr. Helmut R. RosenbauerCo-InvestigatorMax-Planck-Institut fur
Dr. Bruce E. GoldsteinCo-InvestigatorNASA Jet Propulsion
Dr. Marcia M. NeugebauerCo-InvestigatorNASA Jet Propulsion
Dr. Wing-Huen H. IpCo-InvestigatorMax-Planck-Institut fur
Prof. Johannes GeissCo-InvestigatorUniversitat
Dr. Fritz BuehlerCo-InvestigatorUniversitat Bern 
Prof. Hans R. BalsigerGeneral ContactUniversitat
Prof. Herbert S. BridgeCo-InvestigatorMassachusetts Institute of Technology 
Dr. Richard G. JohnsonCo-InvestigatorOffice of Science and Technology Policy 
Dr. Rainer SchwennCo-InvestigatorMax-Planck-Institut fur
Dr. Eigil UngstrupCo-InvestigatorDanish Space Research
Mr. Robert BensonCo-InvestigatorTexas A&M University 
Dr. Edward G. ShelleyCo-InvestigatorLockheed Palo
Dr. Richard M. GoldsteinCo-InvestigatorNASA Jet Propulsion
Dr. David T. YoungCo-InvestigatorLos Alamos National

Selected References

Neugebauer, M., et al., Variation of protons, Alpha particles, and the magnetic field across the bow shock of comet Halley, Geophys. Res. Lett., 14, No. 10, 995-998, Oct. 1987.

Fuselier, S. A., et al., Cometary H2+ and solar wind He2+ dynamics across the Halley cometopause, Geophys. Res. Lett., 15, No. 6, 549-552, June 1988.

Neugebauer, M., et al., Density of cometary protons upstream of comet Halley's bow shock, J. Geophys. Res., 94, No. A2, 1261-1269, Feb. 1989.

Goldstein, B. E., et al., Observations of plasma dynamics in the coma of P/Halley by the Giotto ion mass spectrometer, J. Geophys. Res., 97, No. A4, 4121-4132, Apr. 1992.

Balsiger, H., et al., The Giotto ion mass spectrometer, In--The Giotto Mission--Its Scientific Investigations, ESA SP-1077, edited by R. Reinhard and B. Battrick, pp. 129-148, Mar. 1986.

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