A thermal system for maintaining a temperature of a primary heat load, the thermal system comprising: a reservoir ; a cooling loop originating from the reservoir and returning to the reservoir , the cooling loop comprising: a sub-cooler ; a liquid pump having a suction in fluid communication with the reservoir , the sub-cooler being between the reservoir and the suction of the pump ; a pre-heater ; and an evaporator having a cooling fluid outlet in fluid communication with the reservoir ; and a pressure regulator between the evaporator and the reservoir ; wherein a discharge of the pump is in fluid communication with a cooling fluid inlet of the evaporator ; and wherein the pre-heater is between the discharge of the pump and the cooling fluid inlet of the evaporator ; and a heat rejection loop originating from the reservoir and returning to the reservoir , the heat rejection loop comprising: a pressure regulator ; a vapor compressor having a suction in fluid communication with the reservoir ; a condenser having a hot fluid outlet in fluid communication with the reservoir ; and an expansion valve between a fluid outlet of the condenser and the reservoir ; wherein the pressure regulator is between the reservoir and the suction of the vapor compressor ; and wherein a discharge of the vapor compressor is in fluid communication with a hot fluid inlet of the condenser . a reservoir ; a cooling loop originating from the reservoir and returning to the reservoir , the cooling loop comprising: a sub-cooler ; a liquid pump having a suction in fluid communication with the reservoir , the sub-cooler being between the reservoir and the suction of the pump ; a pre-heater ; and an evaporator having a cooling fluid outlet in fluid communication with the reservoir ; and a pressure regulator between the evaporator and the reservoir ; wherein a discharge of the pump is in fluid communication with a cooling fluid inlet of the evaporator ; and wherein the pre-heater is between the discharge of the pump and the cooling fluid inlet of the evaporator ; and a sub-cooler ; a liquid pump having a suction in fluid communication with the reservoir , the sub-cooler being between the reservoir and the suction of the pump ; a pre-heater ; and an evaporator having a cooling fluid outlet in fluid communication with the reservoir ; and a pressure regulator between the evaporator and the reservoir ; wherein a discharge of the pump is in fluid communication with a cooling fluid inlet of the evaporator ; and wherein the pre-heater is between the discharge of the pump and the cooling fluid inlet of the evaporator ; a heat rejection loop originating from the reservoir and returning to the reservoir , the heat rejection loop comprising: a pressure regulator ; a vapor compressor having a suction in fluid communication with the reservoir ; a condenser having a hot fluid outlet in fluid communication with the reservoir ; and an expansion valve between a fluid outlet of the condenser and the reservoir ; wherein the pressure regulator is between the reservoir and the suction of the vapor compressor ; and wherein a discharge of the vapor compressor is in fluid communication with a hot fluid inlet of the condenser . a pressure regulator ; a vapor compressor having a suction in fluid communication with the reservoir ; a condenser having a hot fluid outlet in fluid communication with the reservoir ; and an expansion valve between a fluid outlet of the condenser and the reservoir ; wherein the pressure regulator is between the reservoir and the suction of the vapor compressor ; and wherein a discharge of the vapor compressor is in fluid communication with a hot fluid inlet of the condenser . <EOS>