A Soyuz rocket sitting on the launchpad holds approximately 347,000 pounds of propellant in each of its four boosters. While this is great for thrusting the craft into orbit, it comes at a heavy price – literally. But what if we could reduce the amount of fuel needed?
Researchers from the Institute of Space Systems (IRS) at the University of Stuttgart, Germany, have been studying a possible propulsion system for space transport, based on an approach referred to as inertial electrostatic confinement (IEC) of plasma sources. This uses an electric field to heat plasma to fusion conditions. The team chose to investigate the phenomena in an IEC device that leads to jet extraction, finding that it could produce ion jets with very high kinetic energy. Their results are published in the journal Vacuum.
Georg Herdrich, deputy head of the Department of Space Transportation at IRS, explains: "Our IRS system produces a jet that can be used in a future advanced electric space propulsion system, saving significant amounts of propellant mass due to its high kinetic energy. Moreover, the system may also be used as an air breathing propulsion system in Earth's thermosphere, giving very low flying satellite systems an increased lifetime as the propulsion system compensates the satellite’s drag.”
Both electric space propulsion systems and air breathing propulsion systems have the ability to reduce the mass of propellant necessary to propel rockets into space. Electric propulsion systems, currently used in Russian satellites, electrically expel propellant at a high speed, thus using less propellant than a chemical rocket. Air breathing systems make use of atmospheric oxygen to burn fuel onboard making the system lighter, more efficient and cost effective. This type of system could be used in the follow-up mission to the Gravity Field and Steady State Ocean Circulation Explorer (GOCE), which intends to map the Earth's gravity field.
The IRS team systematically assessed the jet production from the IEC device and the preliminary characteristics of its discharge using emission spectroscopy. "Taking the IEC’s jet as a point of departure for a future space propulsion system, our first analyses imply that its ion energies are significantly higher than classical ion thrusters," says Herdich.
He adds: “We are testing a thruster prototype in collaboration with industry. Our promising data confirm our well-educated guesses about the jet characteristics and our interpretation enables a variety of new applications. This is interesting, because of the very significant impact a readily developed IEC-based electric space propulsion system would have for a variety of space applications.”
The researchers hope that electric space propulsion systems will take spacecraft to the outer solar system. Perhaps, it will one day enable interstellar flight.
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This article originally appeared in Vacuum 136 2017, Pages 177–183. Syring, C. and Herdich, G. [http://dx.doi.org/10.1016/j.vacuum.2016.10.018]