Electric Propulsion Systems for Space Travel

electric propulsion systems for space
Testing the Radiofrequency Ion Thruster (RIT) at DLR. Image credit: DLR(CC-DY 3.0)

Electric propulsion systems are considered to be particularly promising space technology. Although they produce less thrust, their fuel efficiency is significantly higher than that of conventional chemical engines. Satellites can thus be made considerably lighter and more durable. Additionally, the payload capacity can be increased because of the lower fuel mass needed. Electric engines are therefore of particular interest to interplanetary long-term missions – or for high-performance communications satellites.

Germany has been conducting research into electric propulsion systems for several decades. The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Space Administration in Bonn has been funding the industrial development of electric engines for several years with funds from the German Federal Ministry for Economics and Energy (BMWi). And now, this comes with commercial success:

On 13 September 2017 at the ‘World Satellite Business Week‘ in Paris, ArianeGroup announced the signing of a first production contract for RIT 2X electric propulsion systems for Boeing telecommunication satellites as part of a joint development programme. The propulsion systems are being developed, manufactured and tested by ArianeGroup in Lampoldshausen. The corresponding power supply electronics come from the Airbus locations in Friedrichshafen and Madrid. In addition, a long-term cooperation was agreed, which will ensure the provision of these propulsion systems for future satellites of this product line. The first two electrically-powered communications satellites were built by Boeing and were launched in 2015.

“This propulsion system is a prime example of the success of our long-term and sustained support,” explains Gerd Gruppe, DLR Executive Board Member for Space Administration. “ArianeGroup has succeeded in strengthening the worldwide trust in German advanced technology with strategically well-devised planning. This commitment is now bearing fruit.”

The ordered propulsion systems are based on the so-called RIT (Radiofrequency Ion Thruster) technology. The DLR Space Administration supports the development of these propulsion systems both through contributions from the national funding programme and through the German contributions to the ESA Advanced Research in Telecommunications Systems (ARTES) programme.

“The RIT was able to demonstrate its true potential for the first time in 2001 on the ESA satellite mission ARTEMIS. Due to a malfunction in the launcher, ARTEMIS was put in a lower than intended orbit but the satellite was able to ‘save itself’ and reach its nominal orbit by using the on-board RIT-10 engine. Thanks to its fuel efficiency, the achievable weight savings using an electric engine are particularly high,” says Lisa Martin Perez, who is responsible for ‘Electric Propulsion’ research at the DLR Space Administration.

In addition to various electric propulsion system technologies, the company is also developing its own fully-electric satellite product line at OHB System in Bremen. ‘ELECTRA’ is being implemented in a public-private partnership by Germany and partner countries within the framework of ESA’s ARTES programme. A private partner and the first customer of ELECTRA is the satellite operator SES from Luxembourg.

Solar energy instead of chemical liquid fuels

In contrast to chemical drives, in which the energy is stored in the fuel itself, the energy for electric propulsion systems comes from the satellite’s solar cells. The RIT engines use electromagnetic waves in the radio frequency range in order to ionise the propulsion gas – such as xenon, which is generally used in electric engines – which generates an electric charge. Subsequently, the ionised gas is accelerated by use of a high-voltage grid. As a result, the satellite experiences thrust and is driven in the desired direction.

For this operation, the engines require a sophisticated combination of high voltage and high currents provided by the power supply unit.

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