Independent power generation in aircraft

An aircraft, comprising:

• at least one engine;
• a plurality of independent power units;
• and
• a fuselage,
• wherein each power unit of the plurality of independent power units generates electricity independently of the at least one engine during flight, the plurality of independent power units including at least a first independent power unit that generates first electricity having a first set of electrical characteristics and a second independent power unit that generates second electricity having a second set of electrical characteristics concurrently with the first power unit generating the first electricity,
• wherein the first set of electrical characteristics is different than the second set of electrical characteristics,
• wherein the second independent power unit provides power to an environmental control system (ECS) configured to provide conditioned air to the fuselage, and
• wherein, during flight, the ECS is electrically and pneumatically isolated from the at least one engine.