Galileo is the global navigation satellite system (GNSS) that is currently under final implementation by the European Union (EU) through the European Space Agency (ESA) and the European GNSS Agency (GSA) with two ground operations centres, Oberpfaffenhofen near Munich in Germany and Fucino in Italy. Galileo provides independent positioning and timing information not relying on the Russian GLONASS, Chinese BeiDou or US GPS systems, but fully compatible allowing improved multi-constellation services. The use of the basic Galileo services is free and open to everyone. Galileo is intended to provide horizontal and vertical position measurements within 1-metre precision.

Within the Galileo satellite navigation programme Horst had the opportunity as Technical Manager at industrial system prime level to specify and design the Galileo ground mission segment. Following the change of governance, he was leading the Airbus Defence & Space system engineering support team. Until August 2016 he was responsible as Galileo Exploitation Programme Manager for setting-up the Galileo Exploitation Phase at the European GNSS Agency GSA in Prague. In this position he and his team prepared the tender documentation packages for the future Galileo Service Operator GSOp and for two ground service elements, i.e. the GNSS Service Centre in Spain and the independent Galileo performance Reference Centre in the Netherlands. At GSA he was leading the Initial Services preparation activities resulting in the service declaration in December 2016.