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​​​DS4G Ion Thruster - HiPER Project

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(image courtesy of ESA​ - European Space Agency[1])

The aim of the HiPER project was to define a roadmap for the future of electric propulsion.
Several missions are under study, including a Mars sample return mission, rendezvous with Near Earth Objects, building of infrastructure on the Moon-Earth L1 point and building of infrastructure on Mars. Different electric propulsion subsystems are under study for these missions including Magneto Plasma Dynamic Thrusters (MPDTs), Hall Effect Thrusters (HETs) and Gridded Ion Engines (GIEs). The University of Southampton and Mars Space Ltd are working on the design of GIEs and in particular of a new
concept of GIE called Dual Stage Gridded Ion Engine originally developed by the late D. G. Fearn based on a tetrode extraction system for high energy neutrals and ions used in tokamaks.

The DS4G (DS3G)

At the high end of the performance range of electric propulsion devices, analytical and numerical work is ongoing investigating the prototype design and the mission applications of a new type of Gridded Ion Engine (GIE), utilising 3 or 4 grids rather than the usual 2 or 3. Called Double-Stage 4-Grid (DS4G), this Ion Thruster was originally conceived by the late David G. Fearn built and tested by a team formed by ESA and the Australian National University for the first time at ESTEC in 2005. It can operate at much higher values of specific impulse (Isp ~ 10,000 s to 30,000 s) and power (hundreds of kW), but with lifetimes comparable to those of conventional GIEs, by separating ion extraction and acceleration, which in a conventional GIE are deeply interconnected, with an intrinsic compromise between maximum current density and Isp.​
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 Schematics of a dual-stage ion optics

Ion Optics numerical simulation and high-current HC modelling and design are among the current lines of research.

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Beam ion density, Isp=10,000s. Arbitrary units

A study showed that the DS3G theoretically offers advantages over the conventional GIE in terms of thrust density if the voltage applied in the second stage is 0.6 times (or higher) the one in the first stage.

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Dual-stage GIE Thrust per Area as a function of Acceleration Extraction Voltage Ration (normalized for the regular GIE)

​[1] Bramanti et al.,"The innovative Dual Stage 4 Grid Ion Thruster Concept – Theory and Experimental Results", IAC-06-C4.4.7, 2006.​