Dear Elio Battista, NASAs account of the magnetic interaction with the Earth shows that the thrust is not due to this interaction. This result was totally ignored later by Martin Tajmar and his team when they attacked NASA.
See: Article Measurement of Impulsive Thrust from a Closed Radio-Frequenc...
and refer to "8. Error Sources", see paragraph 3:
The third error is magnetic interaction, which has the potential for a false positive resulting from dc currents in power cables interacting during test article operation with ambient magnetic fields (e.g., local Earth field, magnetic damper) to generate a torque displacement on the pendulum. All dc power cables are a twisted pair or twisted shielded pair to minimize magnetic interaction. The test article is tested in forward, reverse, and null thrust orientations, but dc power cable routing and orientation is the same for all three configurations (power cables come in from the top of the test article), meaning any false positives will be the same magnitude and polarity for all three tests. This is not observed during the test campaign. Sincerely, Eytan Suchard, [email protected]