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Instrument: MAG : Magnetic Field Experiment
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The Magnetometer (MAG) instrument on the Advanced Composition Explorer (ACE)
consists of one electronics box mounted on the spacecraft top deck and of two
sensors mounted at the end of two boom.

Except for minor modifications, the ACE/MAG instrument consisting of a set of
twin sensors and of an electronics control unit is the flight spare from the
instrument currently flying on the WIND spacecraft launched in November of

The ACE/MAG instrument will measure the local interplanetary magnetic field
(IMF) direction and magnitude and establish the large scale structure and
fluctuation characteristics of the IMF at 1 AU upstream of Earth as a function
of time throughout the mission. This experiment will provide:

- continuous data at 3,4 or 6 vectors/sec, and
- snapshot memory data and Fast Fourier Transform data (FFT) based on
24 vectors/sec. acquired on board, working synchronously with blocks
of 512 samples (FFT only) each.

These measurements will be precise, accurate, and ultra sensitive. The basic
instrument is a twin triaxial fluxgate magnetometer system. Each of two
identical sensors is on booms that extend past the end of diametrically
opposite solar panels. The digital processing unit utilizes a 12 bit A/D
converter to easily resolve small amplitude fluctuations of the field, and is
microprocessor controlled. It also incorporates a dedicated FFT processor
developed around high performance DSP integrated circuits, which produces a 32
channel logarithmic spectrum for each axis, synthesized from a "raw" 256 point
linear spectrum. All components of the power spectral matrices corresponding to
the 32 estimates are transmitted to the ground once every 80 seconds, providing
power and phase information together with the corresponding snapshot memory
time series data. As in previous instruments developed at GSFC, high
reliability is obtained by the use of fully redundant systems and extremely
conservative designs. The intrinsic zero drift of the sensors is expected to be
below 0.1 nT over periods of up to 6 months. Electrical "flippers" designed to
simulate a 180 degree mechanical rotation of the sensors, will be used to
monitor the zero level drift associated with aging of electronic components.
The use of advanced statistical techniques for estimating absolute zero levels
is also planned. The instruments feature a very wide dynamic range of
measurements capability, from B1 4 nT up to B1 65,536 nT per axis in eight
discrete ranges; all ranges can be activated either by command or, most
commonly, automatically. The upper range permits end to end testing in the
Earth's magnetic field without the need for special field cancellation coils or
magnetic shields.

The Bartol Research Institute (BRI) of the University of Delaware, in
collaboration with the Laboratory for Extraterrestrial Physics (LEP) at the
Goddard Space Flight Center (GSFC), built and delivered the magnetometer
instrument for the ACE mission. Data processing for the MAG instrument moved to
The University of New Hampshire when C.W. Smith moved there in July 2003.


Online Resources

Instrument Logistics
Data Rate: 0.304 kbps
Instrument Start Date: 1997-08-25
Instrument Owner: University of Delaware, Bartol Research Institute