Introduction
Electrospray (ES) thrusters generate low thrust via the electrostatic extraction of charged species from an electrified liquid. These systems are characterized by the propellant used and emission mode of the ion beam. The most common of these, field emission electric propulsion (FEEP), utilize liquid metals as its ion source to produce positively charged ions and/or droplets and have previously been studied here at NGPDL. Recent developments include nonmetallic ion sources such as ionic liquids (ILs), room-temperature molten salts, that support emission of heavy ions that contribute to high propulsive efficiencies and specific impulses. ILs additionally exhibit low vapor pressure that allow for exposure in vacuum conditions. 

Though ionic liquid ion sources (ILIS) have demonstrated their applicability within micro propulsion, further efforts are required to study higher thrust capabilities by coupling multiple ES emitters in parallel, a process known as multiplexing. High-fidelity modeling of the electro hydrodynamics of ILIS emitters are thus employed to elucidate the varying failure modes and coupling conditions. 

WORKINGS OF ELECTROSPRAY THRUSTERS:

Electrospray thrusters use electrostatic forces to extract charged particles from a liquid and accelerate them to produce thrust. They are efficient and use little power, making them useful for small satellites and deep space exploration.

1. A liquid propellant is fed to a zone with a high voltage electric field. 
2. The liquid’s surface tension and the electric field distort the liquid into a Taylor cone. 
3. At a certain voltage, the electric field overcomes the surface tension and ejects a fine spray of charged droplets. 
4. The droplets are accelerated through small holes using an electrostatic field

Types of electrospray thrusters:

• Field emission electric propulsion (FEEP) : Uses liquid metals to produce positively charged ions and droplets
• Ionic liquid ion sources (ILIS) : Uses room-temperature molten salts to produce salt ion beams
• Colloid thrusters: Uses solvents like doped glycerol and formamide to accelerate charged droplets

APPLICATIONS:

Electrospray thrusters are primarily used for precise attitude control and small orbital adjustments on spacecraft, particularly for small satellites like CubeSats, due to their very low thrust levels but high specific impulse, making them ideal for missions requiring fine maneuvering and long-duration propulsion in space, such as:

• Satellite stationkeeping : Maintaining a satellite’s position in orbit with high precision, especially in geostationary orbits. 
• Attitude control: Precisely adjusting the orientation of a spacecraft by applying small, controlled thrusts. 
• Drag-free control : Minimizing the effects of environmental disturbances on a spacecraft, enabling highly sensitive scientific measurements. 
• Formation flying:Maintaining precise relative positions between multiple spacecraft in a constellation. 
• Deep space exploration:Performing small, precise maneuvers during long-duration missions where low thrust over extended periods is needed. 
• Lunar orbit insertion:Achieving a stable orbit around the moon with low-thrust propulsion. 

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