Hollow Cathode Thruster

Hollow cathodes have a good flight heritage having been used since late ‘60s onboard of Hall Effect Thrusters (HETs) and Gridded Ion Engines (GIEs). Their use as standalone thrusters (HCTs) has been extensively investigated since the year 2000.

Nowadays one of the most important characteristic in space missions is th​e flexibility of the thruster module in terms of performances. HCTs are unique in these terms since they can be used in three different modes hence providing three degrees of built in redundancy:

1. Cold Gas mode: the gas flows in the cathode and is expanded in the nozzle
2. ​Resistojet Mode: the heaters are switched on and they heat the propellant flow before it is expanded in the nozzle
3. ​​Arcjet mode: the discharge is ignited and the flow is heated in the orifice due to collisions between plasma electrons and xenon neutrals and ions

Preliminary tests at Aerospazio on a QinetiQ T5 HCT showed:

• ​Resistojet  Mode: thrust proportional to mass flow rate. Isp up to 60s, power of the order of 30W
• Arcjet mode: thrust 0.3 mN @ Isp=160 s with a power consumption of 35 W

In the frame of an ESA TRP project Mars Space Ltd and QinetiQ have developed an HCT for East-West Station Keeping on board of Communication Satellites.

An optimized QinetiQ T6 HCT has been designed. The thruster does not present any critical modification with respect to a conventional QinetiQ T6 cathode and hence inheriting its robustness and reliability and will have significantly shorter route to qualification than a new thruster development.

The T6 HCT has been tested at Aerospazio and University of Southampton​ showing to outperform the study requirements:

• Resistojet Mode: thrust      proportional to mass flow rate. Isp      up to 60s, power of the order of 60W
• Arcjet mode: thrust 1.81 mN @ Isp=320 s with a power consumption of 195 W
• Arcjet mode with an applied magnetic field: thrust 2.28 mN @ Isp=300 s with a power consumption of 310 W​