| Electric propulsion is an advanced form of spacecraft propulsion with many advantages compared to chemical propulsion. Nano/pico-satellites with masses of a few kilograms or smaller require only tens of micronewtons or less of thrust for station keeping and attitude control. An electrostatic thruster is investigated in the present work as a candidate for small spacecraft due to its inherent small size, low power requirements and propellant usage. Numerical simulations were performed to help in the design of a laboratory scale model of the micropropulsion system. Several configurations of electrodes and emitters were studied for three types of emission: pure droplet spray, mixed droplet-ion and pure ion mode. The cone jet regime was successfully achieved for stable operation of the micro thruster. The parametric studies contributed to an optimized laboratory scale model which was then characterized experimentally. Several physical parameters were concluded to be critical in the operation of the thruster, namely flow rate and electrical conductivity. Doped propellants were therefore prepared and tested for enhanced specific impulse or thrust. The highest thrust and specific impulse were achieved from a single emitter capillary using Glycerol doped with Sodium Iodide and these values can be significantly enhanced in an array configuration. Dual systems were also studied as oppositely charged beams would avoid the use of a neutralizer device normally required to counter charging effects on the satellite. The ejected beams were characterized qualitatively by imaging techniques and quantitatively by current measurements. The prototype designs and methods tested experimentally provide insights and can contribute to a future design of a micro-machined array colloid micro-thruster ready for use in small spacecraft. |
