Electrospray as a Source of Nanoparticles for Efficient Colloid Thrusters

The need for electric propulsion in the thrust range of tens of micro-Newtons has triggered therebirth of colloid thrustertechnology.Theabilitytodeliverthrustattheselevelsinacontrollablefashionwillenhancetheuseofsmall satellites(massessmallerthan some20kg )and theexecutionofspacemissionsinwhichvery accuratepositioning of spacecraftsisrequired.Wepresenthereanovelapproachtothee eldofcolloidthrusters.Likepreviouseffortsituses electrospray as the mean of producing charged colloids. However, it differs in the spraying regime employed. Electrosprays of highly conducting propellants in single cone-jet mode allow the generation of droplets of high specie c charge at operating voltages lower than in the earlier era of colloid thruster research. In this article we use energy analysis techniques to characterize electrospray beams and to measure their thrust and specie c impulse. We have studied three novel propellants: formamide, tributyl phosphate, and the ionic liquid 1-ethyl-3-methylimidazolium bis (trie uoromethylsulfonyl)imide. The thrust, specie c impulse, and efe ciency associated with a single spray of the most conducting formamide solution are typically 0.3 πN, 300 s, and 75% for an acceleration voltage of 1300 V. The electrospray phenomenology presented in this article is diverse. For example, by varying the electrospraying parametersweareabletostudyemissionmodesinwhich1 )solvatedionsaree eldevaporatedfromthejet’ ssurface, 2) both satellite and main droplets result from the jet’ s breakup, and 3 ) only main droplets are emitted.