Currently, a direct, accurate way to measure thrust produced by a Hall thruster on orbit does not exist. A technique able to know the produced thrust will enable timely and accurate maneuvering, a capability particularly important to satellite formation flying. The means to determine thrust directly is achievable by remotely measuring the magnetic field and solving the inverse problem for the Hall current density distribution. The magnetic field was measured by employing an array of eight tunneling magnetoresistive (TMR) sensors capable of milligauss sensitivity when placed in a high background field. The array was positioned just outside the thruster channel on a 1.5 kW CSU Hall thruster equipped with a center-mounted electride cathode. In this location, the static magnetic field is approximately 30 Gauss, which is within the linear operating range of the TMR sensors. Furthermore, the induced field at this distance is approximately tens of milligauss, which is within the sensitivity range of the TMR sensors. Because of the nature of the inverse problem, the induced-field measurements do not provide the Hall current density by a simple inversion; however, a Tikhonov regularization of the induced field does provide current density distributions as a function of time that are shown in contour plots. The measured ratios between the average Hall current and the discharge current ranged from 6.1 to 7.3 over a range of operating conditions from 1.3 kW to 2.2 kW. The temporal inverse solution at 1.5 kW exhibited a breathing mode of 24 kHz, which was in agreement with temporal measurements of the discharge current.
展开▼
