Advancements in Superconducting Electric Propulsion: Comparative Analysis and Progress Update of CHEETA and CRUISE Motors

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This paper summarizes the efforts in developing the world's most power-dense and efficient electric aircraft propulsion motor through the synergistic CHEETA (Center for High-Efficiency Electrical Technologies for Aircraft) and CRUISE (CRyogen-free Ultra-hIgh field Superconducting Electric motor) projects. The partially superconducting (SC) motor being developed under the CRUISE program features an inrunner rotor with an embedded cryocooler and high-temperature superconducting (HTS) field windings, and a slotless stator armature composed of room-temperature conductors. The CHEETA machine has the same high-level features as CRUISE, however, the armature is also cryogenically cooled to achieve the highest possible efficiency and power density. To close the machine design, four key challenges were addressed: (1) integrate a compact and rotationally-compatible cryocooler into the shaft bore with enough heat lift to cool the HTS coils to sub-50 K; (2) design a rotor cryogenic thermal management system (TMS) that minimizes the heat load to the cryocooler's cold head while simultaneously transferring torque; (3) develop robust, conduction-cooled and quench tolerant HTS magnets; (4) construct an air-core armature that maximizes electrical loading and exhibits low ac losses. In the case of CRUISE, successfully overcoming these challenges resulted in a 10 MW design that achieves 40 kW/kg continuous specific power (127 Nm/kg specific torque) and 99.4% efficiency.