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NEAR Magnetometer (MAG)

NSSDCA ID: 1996-008A-03

Mission Name: NEAR Shoemaker
Principal Investigator:Dr. Mario H. Acuna


The NEAR magnetometer will be used to measure the interplanetary magnetic field during cruise mode and to study, from orbit, the possible magnetic field of asteroid 433 Eros The primary scientific objectives are to establish the global characteristics and geometry of the magnetic field (internal, remnant, or surface) associated with Eros and any detectable interaction with the solar wind and interplanetary field. Secondary objectives include detection of the bow shock, boundary crossings, and magnetic signatures of surface features. The details of an intrinsic magnetic field, if one is detected, would place strong contraints on the composition, internal structure and thermal and collisional history of the asteroid.

The magnetometer is a three-axis fluxgate sensor mounted on the feed structure of the high-gain antenna approximately 1 meter from the main body of the NEAR spacecraft. It has 8 dynamic ranges (+/- 4, 16, 64, 256, 1024, 4096, 16384, 65536 nT) and a minimum detectable magnetic signature of 2-5 nT. An output sample is 80 bits, the DC sampling rate is commandable from 0.01 to 20 Hz and the AC is bandpassed from 1.0 to 10.0 Hz. A 20-bit sigma-delta A/D converter is used to digitize the internal data. The telemetry resolution is 16 bits for the magnetic field data and 8 bits logarithmic for the AC filter outputs.

During the slow approach to Eros and the flyby, the magnetometer will be used to look for fluctuations in the magnetic field due to possible shock and bow waves and the wake boundary caused by the interactions with the solar wind. The location of the perturbations will give an estimate of the magnetic field strength. As the spacecraft spirals in to its final 35 km orbit the intrinsic field, if one exists, will be measured. If detectable, the local surface magnetic fields will also be measured. The asteroid surface field can be measured to 45 nT using the asteroid rotation and spacecraft orbital motion.

Alternate Names

  • MAG
  • NEARShoemaker/MAG

Facts in Brief

Mass: 1.5 kg
Power (avg): 1.5 W
Bit rate (avg): 80 kbps

Funding Agency

  • National Aeronautics and Space Administration United States


  • Planetary Science: Fields and Particles

Additional Information

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



NameRoleOriginal AffiliationE-mail
Dr. Mario H. AcunaTeam LeaderNASA Goddard Space Flight Center
Dr. Christopher T. RussellTeam MemberUniversity of California, Los

Selected References

  • Lohr, D. A., et al., NEAR magnetic field investigation, instrumentation, spacecraft magnetics and data access, Space Sci. Rev., 82, No. 1-2, 255-281, 1997.
  • Acuna, M. H., et al., The NEAR magnetic field investigation: Science objectives at asteroid Eros 433 and experimental approach, J. Geophys. Res., 102, No. E10, 23751-23759, Oct. 1997.
  • Acuna, M. H., et al., NEAR magnetic field observations at 433 Eros: First measurements from the surface of an asteroid, Icarus, 155, No. 1, 220-228, Jan. 2002.
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