Magnetic Disturbance Due to the Hemispherical Hole in the Ground for a Building at the Magnetic Test Site

At the Japan Aerospace Exploration Agency, a zero magnetic field is required to test the magnetic characteristics of spacecrafts, satellites and to calibrate magnetometers. This zero-magnetic field is realized by means of a three-axis coil system which can cancel the uniform earth´s magnetic field, but cannot cancel magnetic disturbance because of no magnetically shielded room. Therefore, the magnetic disturbance within and in the vicinity of the zero-magnetic field of a Spacecraft Magnetic Test Site (SMTS) is investigated by comparing the results of three-dimensional (3-D) finite-element analysis with measurements. Distributions of the magnetic disturbance due to three hemispherical objects-the roof, the foundation made of concrete, and the hole in the ground for the SMTS building-are analyzed and compared with those measured by a proton magnetometer. Consequently, it is shown that the hemispherical hole in the ground for the SMTS building, which has weak magnetism and is a little higher than that of concrete, generates a weak magnetic disturbance in the zero-magnetic field of the SMTS