Hybrid propulsion systems

1. A system comprising:

one or more power units configured to output electrical energy onto one or more electrical busses;

a plurality of series propulsion units positionally mirrored across a centerline of an aircraft, each series propulsion unit of the plurality of series propulsion units comprising a respective propulsor of a plurality of propulsors and a respective electrical machine of a plurality of electrical machines, each respective electrical machine configured to drive a respective propulsor of the plurality of propulsors using electrical energy received from at least one of the one or more electrical busses;

a parallel propulsion unit mounted on the centerline of the aircraft, the parallel propulsion unit comprising: a propulsor, a gas turbine engine configured to drive the propulsor, and an electrical machine selectively configurable to:

generate, for output via the one or more electrical busses, electrical energy using mechanical energy derived from the propulsor or the gas turbine engine; and

drive the propulsor of the parallel propulsion unit using electrical energy received via the one or more electrical busses; and

one or more electrical energy storage devices operably coupled to at least one of the one or more electrical busses, wherein the one or more electrical energy storage devices are configured to both:

charge using electrical energy sourced via the at least one of the one or more electrical busses; and

discharge to provide electrical energy to the at least one of the one or more electrical busses.

2. The system of claim 1 , wherein a particular electrical machine of the plurality of machines included in a particular series propulsion unit of the plurality of series propulsion units is configured to:

generate electrical energy using mechanical energy derived from a particular propulsor of the plurality of propulsors included in the particular series propulsion unit; and

output the generated electrical energy onto the one or more electrical busses.

3. The system of claim 1 , wherein the one or more electrical busses comprise direct current (DC) electrical busses.

4. The system of claim 1 , wherein the one or more power units comprise a plurality of power units.

5. The system of claim 4 , wherein an amount of electrical energy generated by each of the plurality of power units is independently controllable.

6. An airframe comprising:

one or more power units configured to output electrical energy onto one or more electrical busses;

a plurality of series propulsion units positionally mirrored across a centerline of the airframe, each series propulsion unit of the plurality of series propulsion units comprising a respective propulsor of a plurality of propulsors and a respective electrical machine of a plurality of electrical machines, each respective electrical machine configured to drive a respective propulsor of the plurality of propulsors using electrical energy received from at least one of the one or more electrical busses;

a parallel propulsion unit mounted on the centerline of the airframe, the parallel propulsion unit comprising: a propulsor, a gas turbine engine configured to drive the propulsor, and an electrical machine selectively configurable to:

generate, for output via the one or more electrical busses, electrical energy using mechanical energy derived from the propulsor or the gas turbine engine; and

drive the propulsor of the parallel propulsion unit using electrical energy received via the one or more electrical busses; and

one or more electrical energy storage devices operably coupled to at least one of the one or more electrical busses, wherein the one or more electrical energy storage devices are configured to both:

charge using electrical energy sourced via the at least one of the one or more electrical busses; and

discharge to provide electrical energy to the at least one of the one or more electrical busses.