Dual-Stage 4-Grid

The Dual-Stage 4-Grid (DS4G) is an electrostatic ion thruster design developed by the European Space Agency,[1] in collaboration with the Australian National University.[2] The design was derived by D. Fern from Controlled Thermonuclear Reactor experiments that use a 4-grid mechanism to accelerate ion beams.

A 4-grid ion thruster with only 0.2 m diameter is projected to absorb 250 kW power. With that energy input rate, the thruster could produce a thrust of 2.5 N. The specific impulse (a measure of fuel efficiency), could reach 19,300 s at an exhaust velocity of 210 km/s if xenon propellant were used.[3] The potentially attainable power and thrust densities would substantially extend the power absorption of current ion thrusters to far more than 100 kW. These characteristics facilitate the development of ion thrusters that can result in extraordinary high-end velocities.[3]

Like with thruster concepts such as VASIMR, the dual-stage-4-grid ion thrusters are mainly limited by the necessary power supply for their operation. For example, if solar panels were to supply more than 250 kW, the size of the solar array would surpass the size of the solar panels of the International Space Station. To provide 250 kW with Stirling radioisotope generators would require roughly 17 tonne of plutonium-238 (for which the US stockpile as of 2013 was no more than 20 kg[4]), and so a nuclear thermal reactor would be needed.

Comparison
For a more comprehensive list, see Spacecraft propulsion § Table of methods.
Specific impulse of various propulsion technologies
Engine Effective exhaust
velocity (m/s)		 Specific
impulse (s)		 Exhaust specific
energy (MJ/kg)
Turbofan jet engine
(actual V is ~300 m/s)		 29,000 3,000 Approx. 0.05
Space Shuttle Solid Rocket Booster
 2,500 250 3
Liquid oxygen-liquid hydrogen
 4,400 450 9.7
Ion thruster 29,000 3,000 430
VASIMR[5][6][7] 30,000–120,000 3,000–12,000 1,400
Dual-stage 4-grid electrostatic ion thruster[8] 210,000 21,400 22,500
Ideal photonic rocket[lower-alpha 1] 299,792,458 30,570,000 89,875,517,874

See also

References
  1. "Dual-Stage Gridded Ion Thruster (DS4G)". ESA Advanced Concepts Team — Advanced Propulstion.
  2. "Dual stage 4 grid thruster". ANU Centre for Plasmas & Fluids.
  3. THE INNOVATIVE DUAL-STAGE 4-GRID ION THRUSTER CONCEPT – THEORY AND EXPERIMENTAL RESULTS
  4. Mosher, Dave. "NASA's Plutonium Problem Could End Deep-Space Exploration". Wired. Retrieved 20 September 2013.
  5. http://www.adastrarocket.com/TimSTAIF2005.pdf
  6. http://www.adastrarocket.com/AIAA-2010-6772-196_small.pdf
  7. http://spacefellowship.com/news/art24083/vasimr-vx-200-meets-full-power-efficiency-milestone.html
  8. http://www.esa.int/esaCP/SEMOSTG23IE_index_0.html
  1. A hypothetical device doing perfect conversion of mass to photons emitted perfectly aligned so as to be antiparallel to the desired thrust vector. This represents the theoretical upper limit for propulsion relying strictly on onboard fuel and the rocket principle.
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