A system for an aircraft includes a compressor for a vapor cycle cooling system (VCCS) for providing cabin air conditioning; an APU for mechanically driving the VCCS compressor; and a starter-generator-motor (SGM) apparatus operable in any of a starter mode, a generator mode, or a motor mode. The SGM apparatus includes: (i) a first coupling element for coupling the SGM apparatus to the APU such that, in the starter mode, the SGM apparatus is used in driving and starting the APU, (ii) a second coupling element for coupling the SGM apparatus to the VCCS compressor such that, in the motor mode, the SGM apparatus mechanically drives the VCCS compressor, and (iii) a set of electrical power terminals at which, in the generator mode, the SGM apparatus provides electrical output power for powering the aircraft electrical system (including the VCCS condenser fan and VCCS evaporator fans) and, in the starter mode and motor mode, the SGM apparatus receives electrical input power from an external electrical power source.