Charging effects on fluid stream droplets for momentum exchange between spacecraft

This dissertation presents the results of research on a novel satellite propulsion concept that relies on the constant transfer of momentum through projection of silicon oil droplet streams through space. The system is primarily applicable to satellites flying side-by-side in formation that require a constant distance between them in order to conduct certain missions such as interferometric synthetic aperture radar observations. Rational for selection of the silicone oil DC705 as the best working fluid is presented. Droplet size, velocity, and spacing needed for station keeping of various satellite mass and separation distance combinations is evaluated. Droplet streams of diameters demonstrated in this study and speeds demonstrated in past research can satisfy propulsion needs of reasonably sized satellites in any earth orbit with at least a kilometer of separation. A continuous droplet stream system requires an order of magnitude less mass than comparable electric propulsion systems and two orders of magnitude less power.;The focus of this study is droplet charging in space due to various mechanisms associated with ambient plasma and photoemissions. Droplet charging is modeled analytically and numerically, primarily with the in-space material charging software called NASCAP. Predicted low earth orbit (LEO) charging is less than a few volts relative to the ambient plasma. Droplets in GEO charge slightly positive in the sun and slightly negative in eclipse during nominal geomagnetic conditions. During high geomagnetic activity, droplets in GEO reach several kilovolts negative potential, which is sufficient to induce Coulomb break-up. Eclipsed polar orbiting droplets reach negative charge potentials of -26V. Lorentz forces will impair droplet collection in the GEO and polar environments but can be mitigated by producing larger droplets and using faster transit speeds between satellites.;A numerical model was developed to simulate droplet stream dispersion caused by electric fields acting between charged droplets. This dispersion can be abated substantially by increasing droplet spacing, which is possible using solenoid valve technology evaluated in laboratory testing. Laboratory charging of DC705 using an extreme ultraviolet lamp in vacuum was conducted. Droplet charge potentials measured in more than 200 experiments were within 4% of NASCAP photoemission simulation predictions. This close correlation indicates that the DC705 material properties determined in this study and the NASCAP algorithm are appropriate for prediction of photoemission charging of DC705.