I haven't seen much about colloidal or electrospray thrusters besides that Wikipedia article and a few questions here. The idea is similar to ion thrusters in that propellant mass is broken into small bits, ionized, and accelerated electrostatically. The difference is in the nature of the small bits.
Ion thrusters can achieve high ionization efficiencies, most propellant atoms that leave are successfully ionized and accelerated.
However If I understand correctly, a colloidal thruster only breaks the propellant into tiny droplets and ionized and accelerates those. The maximum charge you can put on a tiny droplet or solid particle is only a small fraction of the number of electrons because the Coulomb force is so great. I don't know exactly, but perhaps on the order of one charge per one thousand atoms give or take a power of ten, though it will depend on the droplet's or particle's size and nature.
With such a low ionization efficiency, would colloidal thrusters have any advantage over ion thrusters? Simplicity perhaps? Lower weight? Or is my understanding of the technology flawed? Perhaps electrospray thrusters and colloidal thrusters not the same thing?
- Relationship between part dimensions and performance of ion electrospray thruster
- Generating an electric field for a colloid thruster