Micropropulsion

Micropropulsion refers to propulsion systems designed for spacecraft with small masses, typically ranging from tens of kilograms to grams, that deliver very small thrusts in the micro- to milli-Newton range. These systems are specialized for precise attitude control, orbit maintenance, debris avoidance, and formation flying, especially on nanosatellites and small satellites where power and propellant budgets are constrained.

The technology landscape for micropropulsion includes several broad families. Cold gas thrusters use stored, inert gas and provide simple, reliable thrust with moderate specific impulse. Microfabricated chemical thrusters rely on tiny propellant cartridges to generate thrust through rapid local combustion or decomposition, offering higher thrust than cold gas but still on a small scale. Electric propulsion, which uses electrical power to accelerate propellants, is widely studied for its high specific impulse and efficiency. Within electric propulsion, ion and Hall-effect thrusters deliver higher thrust levels at the cost of greater power requirements, while electrospray (field emission) and pulsed plasma thrusters offer very low thrust with complex control. Liquid-metal field emission propulsion (FEEP) and related micro- or nano-scale emitters provide extremely high specific impulse for very small thrusts and are of particular interest for fine attitude control.

Propellants commonly used include inert gases (neon, xenon, nitrogen), ionic liquids, and liquid metals for FEEP, selected to balance performance, storage, safety, and compatibility with spacecraft structure. Power supply from solar arrays or onboard batteries is a critical constraint, influencing overall impulse capability and maneouver times.

Applications include precise orbit maintenance for constellations, drag compensation in low Earth orbit, deorbiting, and precise formation-flying maneuvers, where conventional propulsion would be inefficient or impractical. Ongoing research seeks to improve reliability, scalability, integration with small platforms, and the use of greener propellants.