First Data from the 
Magnetometer Instrument (MAG)

The MAG sensor was the first ACE instrument turned on, shortly after launch on 8/25/97. Shown above is the spin-axis component of the magnetic field as measured by the MAG Primary sensor on the first day of flight. The value of a zero magnetic field is ~2000 in raw counts. Values greater than this are increasingly positive and values less than this are increasingly negative. MAG activation is at ~3000 seconds after spacecraft activation. Following automated internal checks, the instrument autoranges to the appropriate range for the ambient magnetic field. Two automatic range changes can be clearly seen at other times in the figure. The MAG boom deployment is evident as the spacecraft transits the quiet magnetosphere. The MAG boom deployment reverses the direction of the Z-axis of the sensor, thereby changing the sign of the measured field. Throughout the transit of the magnetosphere the magnitude of the magnetic field decreases while range changes provide increased count rates and increased sensitivity. The subsequent transit of the turbulent magnetosheath places the spacecraft in the upstream solar wind near the end of the first day of flight, at which time it was about 10 Earth radii away (~64000 km). Changes in sign of the solar wind magnetic field are normal and expected. Preliminary examination reveals an instrument that is functioning as designed with the onboard FFT and Snapshot buffers working correctly. 

See a video of the deployment [480KB file runs 8 seconds] 

ACE/MAG Project 
Contributed by Dr. Charles Smith, Bartol Research Institute, Univ. of Delaware.