Average satellites often weigh several hundred kilograms. A large proportion of this weight is accounted for by the liquid or gaseous propellant. Rocket operators bear high costs to get them into space. The Chair of Space Systems at TU Dresden, together with other international universities and various companies, is therefore researching propellant-free propulsion systems to control satellites in space.

With conventional propulsion systems, up to 90 percent of the satellite's mass is accounted for by fuel, depending on the mission in question. The propulsion system developed in the E.T.COMPACT ("Compact and Propellant-Less Electrodynamic Tether System Based on in-Space Solar Energy") project has the potential to considerably reduce satellite costs and significantly increase the proportion of usable satellite mass, for example for scientific experiments, antennas or cameras.

The new propulsion system uses only solar energy. Long, conductive strips, known as electrodynamic tethers, are attached to the satellite. When moving through the earth's magnetic field, these tethers generate a voltage. This creates a closed circuit between the tether and the surrounding plasma atmosphere (ionosphere). The force acting on the conductive strip is known as the Lorentz force. This principle is also used in classic electric motors. Tandem solar cells store the electrical energy generated. They consist of two photovoltaic solar cells made of the materials CIGS (copper indium gallium diselenide) and perovskite.

One of the biggest challenges in this process is closing the circuit. Researchers at the Institute of Aerospace Engineering are therefore developing innovative, propellant-free electron emitters. These emitters enable the electrons to leave the conductor band in the direction of the atmosphere and thus close the circuit. The electron emitters are developed and tested in the space simulation chambers of the Chair of Space Systems.

E.T.COMPACT will run for three years and is funded by the European Innovation Council (EIC) as part of the Pathfinder program.

Contact
Prof. Dr. Martin Tajmar
Chair of Space Systems
TU Dresden
Phone: 0351 463-38091
E-mail: