DEVELOPMENT OF A MODELING CAPABILITY FOR ENERGY HARVESTING MODULES IN ELECTRODYNAMIC TETHER SYSTEMS

Open Access
Author:
McTernan, Jesse Kane
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
August 08, 2011
Committee Members:
  • Sven G Bilen, Thesis Advisor
Keywords:
  • debris mitigation
  • orbital energy
  • enrgy harvesting
  • energy
  • space tether
  • electrodynamic tether
  • propulsion
Abstract:
Electrodynamic tethers can be used to harvest energy onboard a spacecraft orbiting the Earth or any planetary body with a magnetic field and surrounding plasma. The motion of the conductive tether in the Earth’s magnetic field generates an electromotive force along the length of the tether. The ionospheric plasma completes the circuit to allow current to flow through the tether and, ultimately, through the energy-handling components on the spacecraft. This energy can be used immediately or stored in batteries, capacitors, flywheels, or other storage devices. As current flows through the tether, the spacecraft loses altitude due to the electrodynamic force created by the flow of electrons in the magnetic field. One can think of the electrodynamic tether system as transforming orbital potential energy into electrical energy. The system can regain the lost altitude by forcing current to flow against the generated electromotive force, creating a thrust in the direction of motion. Electrodynamic tether systems can augment a spacecraft’s performance or enable capabilities that were previously unobtainable, such as energy harvesting while in the Earth’s shadow. The objectives of this research were to evaluate the feasibility, performance, trade-offs, and net benefit of electrodynamic-tether power generation for space missions. Specific objectives included creating system concepts for various classes and sizes of spacecraft, characterizing efficiencies, and comparing alternative storage technologies. Our research has found that large satellites have the potential to harvest as much as kilowatts of power at some load. Small electrodynamic tether systems the size of CubeSats have the potential to harvest 50% more energy than solar panel systems alone and can produce over 40-watts-average power useful during, for example, a 10-minute ground station overpass. An energy storage module was added to our simulation software that models physical storage devices, such as supercapacitors and lithium–ion batteries, and a generic device. It also investigates orbital energy concepts such as in-plane energy changes, energy needed to torque an orbit, and the conservation of energy as orbital energy is transferred into electrical energy. In spite of the enhanced capabilities provided to orbiting spacecraft by electrodynamic tether systems, significant research remains to realize the promise of electrodynamic tether systems as a unique solution to the energy needs of satellites.