A potential difference of the order of 10 kV is applied between the two, which generates a strong electric field at the tip of the metal surface.
Although the ion exhaust velocity is high, their mass is very low, resulting in very weak acceleration forces.
[7] FEEP is currently the object of interest in the scientific community, due to its unique features: sub-μN to mN thrust range, near instantaneous switch on/switch off capability, and high-resolution throttleability (better than one part in 104), which enables accurate thrust modulation in both continuous and pulsed modes.
[9] These features lead to low power losses due to ionization and heating and the capability to use capillary forces for feeding purposes, i.e., neither pressurised tanks nor valves are required.
Moreover, alkali metals have the lowest attitude to form ionized droplets or multiply-charged ions, thus leading to the best attainable mass efficiency.
When thrust is required, a strong electric field is generated by the application of a high voltage difference between the emitter and the accelerator.
[10] The use of LMIS operated on gallium, indium, alkali metals or alloys has also been standard practice in secondary ion mass spectrometry (SIMS) since the 1970s.
The substantial advantage of slit emitters over stacked needles is in the self-adjusting mechanism governing the formation and redistribution of emission sites on the liquid metal surface according to the operating parameters; in a stacked-needle array, on the contrary, the Taylor cones can only exist on the fixed tips, which pre-configure a geometrical arrangement that can only be consistent with one particular operating condition.
The miniaturized FEEP module design with a crown-shape emitter to fit into the standard CubeSat chassis was reported in 2017.
The single-emitter FEEP design of 0.5 mN is commercially available,[12] and its arrayed version development is nearing completion as in 2018.