Dual stage 4 grid thruster

A very new concept in electric propulsion, the Dual Stage 4 Grid (DS4G) ion thruster for interplanetary space craft was successfully tested in late 2005 by the European Space Agency and the Australian National University. Under contract to ESA, the experimental ion engine was developed and manufactured at the ANU in the surprisingly short time of 4 months by a small team of experts lead by Dr Orson Sutherland of the Space Plasma Power and Propulsion Group. The ESA group was lead by Dr. Roger Walker, Research Fellow in Advanced Propulsion for the Advanced Concepts Team and Technical Manager of the project on the ESA side.

ANU and ESA make space propulsion breakthrough

The new computer-based engine design developed by Dr Sutherland specifically for the DS4G allows much higher voltages to be used than previously thought possible, resulting in a more powerful post acceleration of the extracted ions. The thruster was tested in a large space simulation chamber in the ESA Technology centre in the Netherlands at a remarkable 30kV and produced an ion exhaust plume that travelled at 210km/s, over four times faster than state-of-the-art ion engine designs achieve. “This makes it four times more fuel efficient, and enables an engine design far more compact than present thrusters to be achieved” said Professor Boswell, the laboratory head. “This is an ultra-ion engine. It has exceeded the current crop by many times and opens up a whole new frontier of exploration possibilities,” Dr Walker is quoted as saying in the ESA press release.

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ds4g thruster

A team at the Australian National University's (ANU) Space Plasma, Power and Propulsion (SP3) have successfully designed and manufactured a new spacecraft ion engine prototype, under contract to the European Space Agency (ESA), that dramatically improves performance over present thrusters and marks a major step forward in space propulsion capability signalling the beginning of large scale robotic missions to the outer solar system and to the precursor interstellar medium.

The device, called the DS4G (Dual-Stage 4-Grid), was successfully tested by a team of ANU and ESA scientists at the European Space Technology Centre (ESTEC) in the Netherlands in November 2005. The prototype system successfully fired a beam with an exhaust velocity of 210 km/s, four times faster than the current state of the art, making the system 4 times more efficient than what is presently achievable. The DS4G is based on a concept first proposed by David Fearn in 2001 and employs 4 accelerating grids instead of the usual 3 found on contemporary gridded ion engines (GITs). The addition of this fourth electrode in an optimised configuration could make the DS4G concept up to ten times more efficient than the current state of the art and will allow the design of more compact and higher power thrusters. Ion engines are a form of electric propulsion (EP) and work by accelerating a beam of positively charged particles (called ions) away from the spacecraft using an electric field, thus creating thrust. ESA has successfully employed numerous EP systems on board spacecraft including its current Moon mission, SMART-1 and will continue to integrate EP systems into future missions.

ds4g thruster

The DS4G concept is very different to SP3's previous device, the Helicon Double Layer Thruster (HDLT) conceived at the ANU by Dr Christine Charles in 2003, in that it employs accelerating grids to create thrust. "These two technologies are starkly different in their approach, but from SP3's perspective they are complimentary to the overall aim of achieving efficient deep space propulsion" said Professor Rod Boswell, the head of the ANU laboratory.

The ANU was specifically contracted to design and build the DS4G because of its unique know-how in the development of plasma ion sources, and in its success with the development of the HDLT in collaboration with ESA. The system was designed and manufactured from scratch in the extremely short time of 4 months by a dedicated team at the Australian National University. "The success of the DS4G prototype shows what can be achieved with the passion and drive of a capable and committed team" said Dr. Orson Sutherland, the engine's designer and leader of the development team at the ANU. It was because of Dr Sutherlands particular expertise and enthusiasm that the development program became an outstanding success.

'Traditional ion engines use three closely separated perforated grids containing thousands of millimetre-sized holes attached to a chamber containing a reservoir of charged particles. These systems effectively extract and accelerate the ions in one stage, which because of physical constraints limits the extraction potential applied between the first and second grids to 5 kV. The DS4G ion engine solves this limitation by effectively decoupling the acceleration from the extraction process into a two-stage system. This allows for independent throttling of the exhaust velocity but more importantly allows very high accelerating fields to be applied to the second stage without adversely affecting the extraction field. The test model achieved total acceleration potentials as high as 30kV, which represents an ion exhaust plume velocity of 210km/s.

ds4g thruster being tested

This would make the DS4G concept over ten times more fuel-efficient than the system used on SMART-1. "Using a similar amount of propellant as SMART-1, a future spacecraft using our new engine design wouldn't just reach the Moon, it would be able to leave the Solar System entirely," says the ESA press release. Once developed into full flight ready devices, these engines will propel spacecraft to the outermost planets, the newly discovered planetoids beyond Pluto and yet further into the unknown realm beyond the solar system, all with-in the working lifetime of a mission scientist.

Closer to home, these supercharged ion engines could figure prominently in the human exploration of space. With an adequate supply of electrical power, a small cluster of larger, high power versions of the new engine design would provide enough thrust to propel a crewed spacecraft to Mars and back.


ANU design/development team

ESA management & technical supervision

UK ESTEC Electric Propulsion Laboratory

Dr Orson Sutherland, Dr Christine Charles, Mr Peter Alexander, Mr Dennis Gibson and Prof. Rod Boswell

CW from bottom, Dr Orson Sutherland, Dr Christine Charles, Mr Peter Alexander, Mr Dennis Gibson and Prof. Rod Boswell

Ms Marika Orlandi, Dr Orson Sutherland, Mr Pierre-Etienne Frigot, Dr Roger Walker and Dr David Fearn

Left to right, Ms Marika Orlandi, Dr Orson Sutherland, Mr Pierre-Etienne Frigot, Dr Roger Walker and Dr David Fearn


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