E3 Flux-gate Magnetometer

The experiment E3 was a joint venture between the University of Rome and Nasa/Goddard Space Flight Center (GSFC) to get an accurate measurement of the vector magnetic field. E3 used the onboard instrument of two triaxial fluxgate (saturable inductor) magnetometers, mounted on a 2.75-meter boom (approximately 4-meters from the spacecraft spin axis), with the ability to rotate the sensors 90 degrees with respect to each other.

Principal Investigators

Dr. Norman F. Ness || NASA Goddard Space Flight Center
Prof. Franco Mariani || Universita degli Studi di Roma

Instrument Documentation

Original Data Description

  • E3 utilized an automatic inflight range switch to select the optimum dynamic range out of four ranges:minus to plus 16, 48, 144, and 432 nT per sensor.
  • The three analog outputs of the magnetometer were converted into three 9 bit digital words: corresponding digitization resolutions for the four ranges were plus or minus 0.03, 0.09, 0.28, and 0.84 nT, respectively.
  • A nonmagnetic thermally oscillating actuator was used to reorient the sensor unit by 90  degrees to determine all three axes zero levels. The accuracy was approximately plus or minus 0.1 gamma.
  • For telemetry bit rates above 256 bps, vector measurements were made at equal intervals in time ranging from 16Hz to 1Hz depending on the telemetry bit rate.
  • For telemetry bit rates below 256 bps, averages and variances were computed on board for transmission to earth.

Data Availability and Reanalysis

  • The magnetic tapes that stored high-resolution E3 data, at the University of Rome, slowly deteriorated. The tapes are unreadable and thus the detailed, high-resolution 8Hz, data has been lost forever.
  • The best available data today is:
    • 6-second averages of the three components of the magnetic field
    • 6-second variance for each component
    • The field magnitude computed as averages from the detailed data
    • Ness/Mariani et al. dataset was used a lot in publications by Bavassano etc. in the 80s
  • The E3 data has been thoroughly reanalyzed in conjunction with the E2 data and discussed in detail at the Cologne Workshop. This information is compiled in an Action Item List.