Dual mode Same propellant used for both high thrust-, low-specific-impulse (chemical

propulsion) and low-thrust-, high-specific-impulse thrusters (electric propulsion).

Why Ionic liquid Have the potential to be used in either a chemical thrust or an electric mode Hydrazine has been the monopropellant of choice for spacecraft and gas

generators because it is storable and easily decomposed to give good combustion properties

Hydrazine toxic. Recent efforts have been aimed at replacing hydrazine with a high performance nontoxic monopropellant.

Energetic salts hydroxylammonium nitrate (HAN), ammonium dinitramide (ADN), and hydrazinium nitroformate have received attention as potential replacements.

Typicaly these are also mixed with a compatible fuel component to provide improved performance.

Electrospray is a propulsion technology in which charged liquid droplets or ions are extracted from an emitter via an applied electric field.

Electrospray liquids with relatively high vapour pressure boil off the propellant and produce an uncontrolled low performance emission.

Ionic liquids candidates for electrospray propulsion due to their negligible vapor pressure and high electrical conductivity

Ionic liquid emissions can range from charged droplets to a purely ionic regime (PIR)

What is imidazole ionic liquid Their capability as electrospray propellants. Particularly those based on the

[Emim]+ Capable as solvents. Many imidazole based ionic liquids tend to have

solubility properties close to those of methanol and ethanol. Properties physical

Essentially a molten, or liquid, salt For dual mode high density low melting temperature and low viscosity are

desired traits common to both propulsive modes in the dual mode system because they do not have significant effect on the operation of each thruster but represent the storability of propellants only

Low viscosity aids in transporting the propellant from the tank and its subsequent injection into either type of thruster

Low melting temperature is desired so that the power required to keep the propellant in liquid form is minimal

High density is desired to accommodate a large amount of propellant in a given volume on a spacecraft

Comparison with hydrazine Table 1. Density viscosity electrical conductivity and surface tension

reported in the table are at a T=298K. [Bmim][NO3] T=379K. properties found in the literature vary slightly due to differences in experimental

technique and purity of the ionic liquid sample. In general the results agree within less than 1%.

Viscosity of the ionic liquids much higher than typical chemical propellants.

Disadvantages Electrochemical properties should be assessed in terms of the likelihood of

the candidate ionic liquid to attain PIR emission because as mentioned operation in the mixed or droplet regime causes the efficiencies of the thruster and specific impulse to drop drastically

Advantages Of dual mode: provide higher mission flexibility in terms of the ability to

dictate maneuvers as mission needs arise on orbit rather than before launch. Single propellant: provide maximum flexibility and significantly reduces the

system mass and volume over a spacecraft using separate propellants for each thrust mode

Analysis of the performance Equilibrium combustion analysis is conducted using the NASA chemical

equilibrium with Applications (CEA) computer code

Performance Hydrazine monopropellant thrusters operate around 243 s because the

catalyst bed cannot handle the high combustion temperature. None of the ionic liquids show performance comparable to that

Performance of the ionic liquids is slightly more promising in terms of density specific impulse

Research Dual mode system concept using a single ionic liquid propellant in chemical

monopropellant Electric electrospray modes has the potential to achieve mission flexibility

gains and mass savings over a system using separate propellants for each mode

Data on their properties are not yet available Analysis of the equilibrium combustion products table 3 indicates a large

amount of solid carbon in the theoretical exhaust gases, indicating incomplete combustion and leading to the poor performance of the ionic liquids