. Arcjet Thruster Influence on Local Magnetic Field Measurements from the GOES-16 Magnetometer

Abstract
GOES-16 is the first satellite launched from NOAA's next-generation Geostationary Operational Environmental Satellite (GOES)-R series. Observations from GOES-16 are used by NOAA to provide terrestrial and space weather forecasts, warnings and alerts. The magnetometer (MAG) on GOES-16, which monitors the geomagnetic field, consists of two tri-axial fluxgate magnetometers mounted on an 8.5 m boom. GOES-16 uses hydrazine arcjet thrusters, and when the arcjets are fired a large magnetic field disturbance contaminates the MAG data. Here, the characteristics of the contamination are described and we suggest possible physical mechanisms for the magnetic field disturbance. The arcjet disturbances occur for ~90 minutes approximately every 4 days, and the contamination renders the MAG operationally useless to NOAA without a correction to the data. The arcjets create step changes in the geomagnetic field observations of up to about 20 nT (~20% of the nominal field strength). We suggest two separate physical mechanisms: a large-scale diamagnetic effect caused by the dense plasma in the thruster plume, and a local current source near the spacecraft caused either by the current that drives the arcjet or by plasma pressure gradients near the thruster.