Magnetic Dipole Moment Determination Using Near-Field Magnetic Gradient Tensor Data

Determination of the magnetic dipole moment of a spacecraft is a key issue for magnetic cleanliness and attitude control of various space scientific spacecraft. Two main methods, namely the multiple magnetic dipole modeling method and near-field analysis, have been used with good results inside a coil facility for prelaunch magnetic testing of a spacecraft. When field-canceling coil sets are unavailable, or coil feedback controls are inadequate to compensate for time-varying geomagnetic fields, determination of the magnetic signature of a spacecraft from measurements of field components is compromised. Therefore, we propose a magnetic dipole moment determination method using magnetic gradient tensor data without any coil facility, which is based on the fact that the time variation of the gradient tensor of the geomagnetic field is very small compared with that of field. We improve the near-field analysis method by expanding the magnetic gradient tensor in a series of spherical harmonics, obtain sets of near-field equations using Fourier analysis, and solve these equations to determine the dipole-moment components. The proposed tensor method can effectively suppress the interference from time variations of ambient magnetic fields. Simulations and experiments have been conducted to prove the validity, robustness, and accuracy of the tensor method.