A Hall Effect Thruster propelled by water vapour is investigated at the Imperial Plasma Propulsion Laboratory. For that purpose,
a water vapour feed system is designed, optimised and tested, with the major objective of keeping water in vapour state at all times.
This system primarily consists of a mass flow controller, a flow restrictor, and a heating and pressure monitor system capable of
identifying under which conditions water condensation occurs. A hanging pendulum thrust balance is used to measure the thrust
on the power range of Pd = 600 − 1600 W. Different magnetic field strengths and mass flows are investigated to determine the
conditions in which the highest efficiency can be achieved. Then, a comparison between water vapour and oxygen (intended to
be the propellant of a water electrolysis Hall Effect Thruster) is included. The results show that oxygen is approximately 20 %
more efficient than water vapour under the same operating conditions. Overall, the highest thrust measurement recorded with water
vapour was 20.0 ± 0.2 mN; with a specific impulse of 2039 ± 20 s and an anode efficiency of 12.5 ± 0.3 % at the largest discharge
power of investigation (Pd = 1600 ± 1 W).