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NEAR's magnetometer will build up a magnetic map of Eros, telling us how strongly magnetized the material of Eros is and how the chunks of magnetic material are arranged. The magnetometer sensor is mounted inside the tube that supports NEAR's high-gain antenna. The magnetometer measures the strength of the magnetic field at the spacecraft 20 times per second, with the dynamic range of the output ranging from 4 nanotesla (nT) to 65,536 nT. For comparison, the strength of the magnetic field at Earth's surface is 30,000-60,000 nT. The magnetometer works by measuring the strength of a magnetic field passing though a coil of wire wound around a core of magnetic material (the "fluxgate" method). Since the magnetic field at the spacecraft can be in any orientation, NEAR's magnetometer uses three coils with orthogonal orientations. The three measurements are added vectorially to get a full, accurate measurement of the field strength and orientation. The signal can be digitally filtered and resampled onboard the spacecraft to lower the output rate, and recorded on the spacecraft for playback to Earth. Instruments similar to NEAR's magnetometer were also flown on Pioneer 10 and 11, Voyager 1 and 2, and some of the lunar Apollo orbiters.
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