This paper proposes solid rotor Interior Permanent Magnet (IPM) machine for an aircraft starter-generator. The key challenge in the design is to satisfy two operating conditions which are high starting torque and high speed continuous operation. A Surface mounted PM machine designed for such an application is used as a benchmark. Then, the IPM machine is designed adopting a solid rotor to have a maximum mechanical stress level well below the material Ultimate Tension Strength (UTS) and minimal rotor eddy current losses. A detailed design is carried out through Finite Element (FE) electromagnetic and structural analysis. The static and dynamic structural analyses are presented. Several novel approaches to minimize the rotor eddy current losses are investigated. It is shown that the proposed solid rotor concept for IPM fulfils both high torque and high speed design requirements whilst satisfying the structural and magnetic limitations.