Energy Harvesting

SEEPS Concept

The Space Environmental Electrical Power Subsystem (SEEPS) is a proposed spacecraft power subsystem that harvests energy from the space environment. Phenomena that are under study for SEEPS include electromagnetic radiation (macroscopic particle impacts), changes in spacecraft potential (plasma interactions), and Hall current (magnetic field interactions), which can be harnessed and converted to DC electrical power.

Electromagnetic Radiation

Hypervelocity particles routinely impact spacecraft. Upon impact, the particle ionizes itself and a portion of the spacecraft, producing an expanding plasma that radiates over a broad frequency band. The resulting electromagnetic pulse contains a significant portion of the impact energy in frequencies that terrestrial harvesting antennas have captured. In February 2019, we conducted an experimental campaign at the NASA Ames Vertical Gun Range in order to characterize the emission from impact plasma. Adjusting for amplifier gain and space loss, a satellite-mounted antenna would produce an 800 mV peak-to-peak pulse from this impactor over approximately 1 μs duration.This translates to a 70 mW short duration pulse for this size impact and antenna design.

Spacecraft Potential

Objects immersed in a plasma build up a net surface charge due to the difference in flux of electrons and ions at the surface along with the photoelectric effect and other secondary effects. Depending on the spacecraft parameters and plasma environment, the charging can vary from positive tens of V to negative kV. This effect can be used to generate power by placing a load either between two differentially charged portions of a spacecraft, a spacecraft chassis and a small probe, or two tethered bodies. Methods of inducing this difference include isolation of the sunlit and shadowed parts of the spacecraft, geometries prone to shadowing, and using passive electron emitters such as triple junctions and knife-edge field effect emitters.

Hall Current

Phenomena where the extractible energy scales with spacecraft length rather than area are necessary for maintaining a small frontal area and reducing the effects of atmospheric drag. The (v x B) contribution to spacecraft charging resulting from orbital motion through the Earth's magnetic field is well known and has been studied extensively through experiments on the shuttle and International Space Station. The electric field resulting from (v x B) in a typical low Earth orbit is approximately 0.4 V/m, which can induce currents through a spacecraft body. The estimated available power is on the order of 10 mW. These currents can be enhanced through active and passive electron emitters, and through design of the spacecraft material, geometry, and orbital orientation.