Development of A Magnetically Levitated Suspension/Rotation Mechanism for Measuring Roll Damping Coefficient of a Hayabusa Capsule

Aerodynamic characteristics measurements in a hypersonic rarefied wind tunnel environment are being attempted at Japan Aerospace Exploration Agency (JAXA) to improve the reliability of rarefied aerodynamic instability evaluation accuracy for a sample return capsule (SRC) using spin stability to maintain attitude stability by implementing a small mimic model of the SRC. In measuring the roll damping coefficient, an indicator of spin rate damping, a motor rotates the capsule, and the free run damping is then evaluated when the power is turned off. For motors with mechanical ball bearings, it is impossible to estimate the damping of pure aerodynamic friction due to the significant rotational loss of the bearings. Therefore, we proposed a suspension/rotation mechanism that theoretically generates no cogging torque and iron loss. The mechanism uses magnetic levitation (MagLev) technology to support the rotor without mechanical contact by magnetic force and a BLDC motor with a coreless coil that does not produce cogging torque. This system allows for a highly accurate evaluation of the damping caused by aerodynamic friction. Finite Element Analysis (FEA) was used to optimize the design of the magnetic bearing and BLDC motor. As a result, both a magnetic bearing that satisfies the desired control range and a motor capable of accelerating the rotor to reach the desired speeds were designed. Furthermore, based on the results of FEA, a numerical model was built, and its dynamic characteristics were simulated. As a result, it was found that the designed mechanism had high stability for operation in the rarefied wind tunnel.