A cooling system, comprising: a first heat exchanger for cooling a refrigerant; an expander configured to receive the refrigerant from the first heat exchanger; at least one compressor configured to compress the refrigerant; an ejector configured to receive the refrigerant from the expander as a motive stream that evacuates and compresses the refrigerant from an evaporator; a liquid separator coupled to an output of the ejector and configured to provide liquid refrigerant to an evaporator loop and vapor refrigerant to the at least one compressor; and the evaporator loop comprising: an expansion device positioned to expand the liquid refrigerant from the liquid separator; and the evaporator configured to receive the refrigerant from the expansion device, heat the refrigerant from a heat load, and pass the refrigerant to the ejector, characterised in that the at least one compressor comprises a first compressor configured to compress the refrigerant to a first pressure, and a second compressor configured to compress the refrigerant to a second pressure that is greater than the first pressure, the system further comprising: a shaft coupled to the first and second compressors (304, 306), and to the expander, to provide power to the first and second compressors (304, 306) from the expander; and a second heat exchanger for cooling the refrigerant from the first compressor, and passing the refrigerant to the second compressor. a first heat exchanger for cooling a refrigerant; an expander configured to receive the refrigerant from the first heat exchanger; at least one compressor configured to compress the refrigerant; an ejector configured to receive the refrigerant from the expander as a motive stream that evacuates and compresses the refrigerant from an evaporator; a liquid separator coupled to an output of the ejector and configured to provide liquid refrigerant to an evaporator loop and vapor refrigerant to the at least one compressor; and the evaporator loop comprising: an expansion device positioned to expand the liquid refrigerant from the liquid separator; and the evaporator configured to receive the refrigerant from the expansion device, heat the refrigerant from a heat load, and pass the refrigerant to the ejector, an expansion device positioned to expand the liquid refrigerant from the liquid separator; and the evaporator configured to receive the refrigerant from the expansion device, heat the refrigerant from a heat load, and pass the refrigerant to the ejector, characterised in that the at least one compressor comprises a first compressor configured to compress the refrigerant to a first pressure, and a second compressor configured to compress the refrigerant to a second pressure that is greater than the first pressure, the system further comprising: a shaft coupled to the first and second compressors (304, 306), and to the expander, to provide power to the first and second compressors (304, 306) from the expander; and a second heat exchanger for cooling the refrigerant from the first compressor, and passing the refrigerant to the second compressor. a shaft coupled to the first and second compressors (304, 306), and to the expander, to provide power to the first and second compressors (304, 306) from the expander; and a second heat exchanger for cooling the refrigerant from the first compressor, and passing the refrigerant to the second compressor.