Experimental and numerical comparison of iodine and noble gas (Xe, Kr and Ar) plasmas for electric propulsion

Since the 1980s, the main propellant for electric space propulsion has been the noble gas xenon, which is a heavy atom with a relatively low ionization threshold. However, because of strong market volatility and growing demand within the space industry, a suitable, more sustainable, alternative that gives comparable performance is needed. Other noble gases, such as krypton or argon, have already been demonstrated, but are generally less efficient and have a lower storage density that requires larger and heavier tanks. Iodine is an element that is close to xenon in the periodic table and is increasingly viewed as a viable alternative propellant despite its molecular and reactive nature. In this work, we investigate low-pressure iodine plasma discharges relevant to electric propulsion and demonstrate why iodine in particular is a promising propellant compared with other noble gas alternatives. Experiments carried out using several different devices, as well as computations using a range of numerical simulations (including 0D and 1D fluid models, and particle-in-cell simulations), make it possible to identify operating regimes for which iodine is a superior propellant.