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Each of the four MMS spacecraft has eight high-speed ion sensors and eight high-speed electron sensors (packaged in pairs as four dual ion spectrometers (DIS) and four dual electron spectrometers (DES)). These dual spectrometer packages are evenly distributed around the spacecraft perimeter so that full azimuthal sampling of phase space does not depend on the spin of the spacecraft as had been common for previous missions. This allows sampling at speeds limited only by the stepper speeds of the spectrometer high voltage power supplies and the counting statistics possible within the measurement accumulation times.
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An important consequence of this approach is that each 3D phase space distribution is "stitched together" from the measurements of those eight spectrometers, which under certain environmental conditions can present an inter-calibration challenge that should be evaluated and managed as part of the user's data analysis approach. |
Fields of View (FPI Skymap)
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