Magnetic field cancellation techniques for the Mars Global Surveyor solar array

The Mars Global Surveyor spacecraft carries a sensitive magnetometer system to detect and characterize the intrinsic magnetic field of Mars, if one exists. The use of booms to place the sensors remote from the spacecraft was not possible due to resource constraints. Instead, the sensors were mounted at the outer edge of the solar array, in close proximity to strings of solar cells. The current geometry in the array was optimized with a piecewise linear simulation to minimize the magnetic field generated at the sensor by the circulating currents under all operating conditions. A number of novel techniques were used in achieving magnetic field cancellation including carefully chosen circuit path lengths with zero area in selected strings, and sensitive magnetic verification tests in the Earth´s field with a resolution of 1 part in 200000. The results show that the field generated by the array at the sensor location during the Mars mapping phase of the mission and under nominal conditions will be less than 0.4 to 0.6 nT (1nT=10^-5 Gauss) under full solar illumination. The design is also reasonably tolerant of string failures. This major achievement would not have been possible without a close and synergistic interaction among the manufacturer, scientists and spacecraft engineers during the design, simulation and test of the solar array