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Ion Mass Spectrometer

NSSDCA ID: 1971-024A-06

Mission Name: ISIS 2
Principal Investigator:Dr. John H. Hoffman


The magnetic ion-mass spectrometer experiment was flown to measure the distribution of the concentrations of the positive ion species as a function of time and position, with particular interest focused on the polar wind particles. The instrument had two ion detector systems, and mass scanning through the range from 1 to 64 atomic mass units (u) was accomplished in two sections, 1 to 8 u and 8 to 64 u. Two ion beams emerged from the magnetic sector of the instrument and were simultaneously detected by electron multipliers and log electrometer amplifiers. A circuit following each amplifier detected the peak amplitude of the ion current. This peak value, rather than the entire mass spectrum, was transmitted in order to reduce the required telemetry bandwidth. In this mode of operation, the complete mass range was scanned in 1 s. A backup mode was provided that produced an analog output with a sweep period of 8 s. This experiment operated nominally after launch with most of the data obtained in the peak mode and while the satellite operated in the cartwheel mode. For about 2 min per pass over Ottawa, Canada, the experiment operated in the analog mode. Inflight calibration was achieved by comparing ion concentration measurements at appropriate altitudes, i.e., where a single ion species predominated, with electron density data from the sounder on board. Other comparisons were made between the spectrometer output and measurements obtained from other related experiments on board. NSSDC has all the useful data that exist from this investigation.

Alternate Names

  • ISIS2/IonMassSpectrometer

Facts in Brief

Power (avg): 7 W

Funding Agency

  • NASA-Office of Space Science (United States)


  • Space Physics: Ionospheric Studies
  • Space Physics: Magnetospheric Studies

Additional Information

Questions and comments about this experiment can be directed to: Dr. Dieter K. Bilitza



NameRoleOriginal AffiliationE-mail
Dr. John H. HoffmanPrincipal InvestigatorUniversity of Texas, Dallas
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