spase://CNES/NumericalData/CDPP-AMDA/ICE/ice-mag-p21

The coordinate resolution for the magnetic field components is the I,S coordinate system, defined by the JPL group before launch. I is the unit vector in the direction of the ICE spin axis (positive in the northward direction), and S is the unit vector from the space- craft to the Sun. The Z-axis ia equal to I, the Y-axis to the nor- malized cross-product I x S, and the x-axis to Y x Z. The I,S co- ordinate system us approximately the same as the Solar Ecliptic (SE) system since the spacecraft Z-axis is maintained within half a degree of perpendicular to the Ecliptic plane. (SE is defined the same way as GSE, but with the spacecraft [point of observation] substituted for Earth).