An innovative design strategy has been set up which is capable of optimising both the electromagnetic as well as the thermal design of permanent magnet synchronous machines (PMSM) for aerospace actuation systems. This has been achieved by linking up the electromagnetic design process and motor housing design process for an overall minimum mass. A validation process was initially performed on a PMSM to ensure the correct functionality of the thermal model. Tests were carried out to calibrate the model with experimental data. This paper further describes the adopted optimisation procedure of a 12.75Nm - 2000rpm, horizontally mounted, 12 slot 14 pole Aerospace Permanent Magnet Synchronous motor and highlights the significant weight and volume saving capabilities.