Atmosphere–Exosphere Angular Momentum Exchange Rotor (AER)

Atmosphere–Exosphere Angular Momentum Exchange Rotor (AER)
Overview
This proposal presents a conceptual system that utilizes a massive rotating structure spanning the upper atmosphere to the thermosphere to exchange angular momentum among Earth’s rotational energy, atmospheric kinetic energy, and orbital structures.
Unlike existing concepts such as the Space Elevator, Orbital Ring, or Electrodynamic Tether, the distinctive feature of this proposal is its direct utilization of the atmospheric density gradient itself.
Background
Earth’s atmosphere exhibits significant density variation with altitude:
•  Stratosphere: approximately 10–50 km
•  Mesosphere: approximately 50–85 km
•  Thermosphere: above approximately 85 km
In particular, the transition region from the mesosphere to the thermosphere experiences a sharp decrease in gas density.
If a large rotating structure is placed in this boundary region, one side of the rotor blades would move through relatively dense atmospheric layers, while the other side would move through the extremely rarefied thermosphere/exosphere. This asymmetric environment creates unique conditions not found in conventional wind turbines or orbital structures.
Basic Structure
The proposed configuration is as follows:
•  An orbital ring or shell structure encircling the Earth
•  Massive rotors suspended from the shell
•  Rotor centers positioned near the mesosphere
•  Rotor blades extending partially toward the stratosphere on one side and toward the thermosphere on the other
•  A sealed gas-filled space inside the rotor
The rotor diameter is assumed to be 10–20 km or larger.
Hypotheses
Hypothesis 1
When the rotor rotates, the internal gas would form a large-scale pressure gradient due to centrifugal force, potentially generating sustained circulatory flow inside the rotor.
Hypothesis 2
Temperature and density differences between the stratospheric and thermospheric sides could induce asymmetric heat transport within the internal fluid.
Hypothesis 3
By installing a power generation system that utilizes the internal circulatory flow, part of the rotor’s rotational energy could be converted into electricity.
Hypothesis 4
Through frictional interaction between the rotor and the atmosphere, angular momentum exchange with Earth’s rotational system would occur. As a result, energy transfer could take place among the Earth, atmosphere, rotor, and orbital ring.
Research Challenges
Aerodynamic Challenges
•  Drag evaluation at altitudes of 80–120 km
•  Shock wave formation conditions
•  Aerodynamic stability of ultra-large-scale blades
Structural Challenges
•  Material strength for 20 km-class rotating bodies
•  Vibration mode analysis
•  Resonance avoidance
Orbital Mechanics Challenges
•  Torque transmission to the ring structure
•  Quantity of angular momentum exchange with Earth’s rotation
•  Long-term stability
Thermodynamic Challenges
•  Modeling of internal fluid circulation
•  Heat transport between the thermosphere and stratosphere
•  Power generation efficiency evaluation
Relation to Existing Research
This proposal has connections with the following research areas:
•  Orbital Ring
•  Tethered Ring
•  Electrodynamic Tether
•  Momentum Exchange Tether
•  Rotating Space Habitat
•  Atmospheric Energy Harvesting
However, it differs from existing concepts in that it directly places a rotating structure within the atmospheric density gradient region and utilizes dynamic coupling with Earth’s rotational system.
Conclusion
At present, the feasibility of this concept remains unclear.
Nevertheless, it offers a novel and unexplored research theme:
“Angular momentum exchange via massive rotating structures in the upper atmosphere.”
In particular, it holds theoretical value from the perspectives of:
•  Utilization of Earth’s rotational energy
•  Energy exchange between the atmosphere and orbital structures
•  Megastructure engineering