This chapter focuses on understanding the behavior of the extremely low frequency (ELF) electric field emissions of EUTs from spacecraft subsystems and on reviewing reliable equivalent models combining measurement techniques in order to acquire a complete system electromagnetic cleanliness. More precise time variations of the electric fields produced by spacecraft equipment have to be characterized, measured, and modeled. The proposed methodology is employing equivalent dipole modeling (EDM) to describe the ELF electric field spectral dependency. Each spectral component of the measured field is considered isolated and produced by one electric dipole. In order to validate the accuracy of the proposed methodology, various ELF signals in different distances are studied. In addition, since the validation of the proposed methodology would require “on ground” measurements and due to the low-frequency range, test facilities decoupling techniques are discussed. Moreover, early considerations including contributing phenomena for the complete spacecraft system modeling are reviewed.