A superconducting magnetic bearing (SMB) [1] uses magnetic levitation technology based on field cooling, which achieves its non-contact rotation with low power consumption due to friction. Because of this feature, it has been applied to many engineering applications including polarization modulator microwave background radiation (CMB) [2]. The SMB consists of a ring-shaped High Temperature Superconductor (HTS) bulk as the stator and a ring-shaped permanent magnet (PM) as the rotor.
When SMB is to be used for a space application, the operational condition on the ground and space become difference due to the effect of the gravity. As a result, performance of SMB can be difference due to the nature of levitating system. One of the potential different characteristics with a presence of gravity is the energy loss during the rotation. When the rotor is levitated on the ground, PM moves from the original position where the PM is field cooled due to gravity. This causes eddy currents in the superconductor which results losses. On the other hand, in the space environment, there is no gravity, therefore there is no change in the position of the PM, and thus no loss is expected with this mechanism.
In this paper, we carried out an experiment using a prototype small experimental platform of axial type SMB and estimate the effect of gravity to the loss. The levitational force and rotational loss were measured by creating a structure in which the PM does not change its position due to gravity. We report the results of the measurements and also explain its implication by using an electromagnetic model.

Keywords: superconducting magnetic bearing, rotational loss