Progress on vacuum-to-air mass calibration system using magnetic suspension to disseminate the Planck-constant realized kilogram

The kilogram is the unit of mass in the International System of units (SI) and has been defined as the mass of the International Prototype Kilogram (IPK) since 1889. In the future, a new definition of the kilogram will be based on precise measurements of the Planck constant. The new definition will occur in a vacuum environment by necessity, so the National Institute of Standards and Technology (NIST) is developing a mass calibration system in which a kilogram artifact in air can be directly compared with a kilogram realized in a vacuum environment. This apparatus uses magnetic levitation to couple the kilogram in air to a high precision mass balance in vacuum. Technical details of the levitation technique, the vacuum-to-air calibration system, and vehicles for transferring masses into and out of vacuum will be presented.