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Completed TRL 3 (started at 2, targeting 4)
The electrostatic solar wind sail (E-sail) is a propellantless propulsion system that can harness the solar wind plasma for continuous thrust. In this project, we plan to build a unique and innovative thrust stand to quantify the thrust produced by imparting an ion beam onto an electrostatically charged tether in a vacuum chamber. Measuring E-sail thrust has not been done before. We plan to compare the thrust produced from the lab with a validated plasma model we plan to develop. Other NASA (GRC & JPL) thrust stands available are typically built for larger mass systems, such as electric propulsion, and would be time consuming and costly to adopt for the light-weight, E-sail tether systems. Therefore, we aim to leverage existing thrust stand technology and develop a design specific to measuring thrust for E-sail tethers. Our goal is to build, design, and test a unique E-sail thrust stand and validate with a plasma model to raise the acceleration phenomenon TRL from TRL 2 to TRL 4.
The E-sail technology takes advantage of the solar wind ions streaming radially from the Sun. The electrostatically charged tether repels the ions, exchanging momentum, and provides a continuous source of thrust without any propellants. As the E-sail moves further from the Sun, the force drops as 1/r compared to the 1/r2 drop experienced by a solar sail. This 1/r force relation dramatically increases the distance an E-sail can effectively accelerate as it travels away from the Sun, which can be out to 25 AU, 5 times further out than a 1/r2 force relation would allow. Therefore, a heliopause or interstellar mission would be achievable for a developed E-sail mission that could provide at least 10 AU/year escape speeds for a 500 kg spacecraft. E-sail thrust can also be improved by increasing the tether potential or by increasing the tether length, introducing trivial amounts of mass. Our CIF project aims to solidify the thrust estimates of an E-sail in solar wind conditions, within an order of magnitude, so that scientists and program leaders are more willing to invest in this propellantless technology. Currently, the leading estimates of the thrust metric varies by 1-2 orders of magnitude from ~10s of nN/m to ~1000 nN/m, for 1 AU solar wind conditions. To date, direct thrust measurements have not been made for the electrostatic sail, but have been done so for the magnetic sail and solar sail.
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