Future directions for Electric Propulsion

All carbon ion engine

The thrust density of an Electric Propulsion (EP) engine can be improved by replacing traditional molybdenum components, which degrade at high power levels due to sputtering, with carbon components that have demonstrated a considerable increase in lifetime. An all carbon engine has been manufactured, and carbon grids have already successfully passed vibration and shock testing.

Thrust vectoring

The small thrust offset from the spacecraft centre of mass that occurs during thrust, can lead to tens of kg propellant wastage. Typically compensation is achieved by heavy gimbal systems. Alternative lightweight mechanisms have been designed and tested by QinetiQ using piezoelectric actuators to move the screen grid relative to the acceleration grid.

Lightweight mechanisms using piezoelectric actuators are used to compensate for the offset between the spacecraft centre of mass and the thrust vector

Multiple thruster operation

In addition to higher unit power levels, future missions will include multiple thrusters that will need to operate simultaneously. QinetiQ is evaluating the interactions of exhaust plumes from multiple thruster operation in our test chambers.

Thruster scaling

Studies have also considered thrust increase by enlarging the chamber diameter combined with an increase in ion beam current. With alternative propellants, this offers the scope for 10kW class engines in conjunction with nuclear or solar power systems.

Similarly, work is also underway to examine scaling down the technology to <~1mN levels for fine control needs.

Integrated electric propulsion systems

Although electric propulsion systems are often advantageous for specific applications, there are disadvantages in combining chemical or cold gas thrusters for attitude control and ion engines for orbit control and transfer. Consequently, QinetiQ has developed hollow cathode thrusters for attitude control, and filament overwound tanks, which allow a common power conditioning unit and propellant storage/feed system.

Hollow cathode thruster for attitude control