Three leading aerospace companies from Europe are advancing plans to merge their satellite divisions in a transaction valued at 10 billion euros, as the region works to boost its competitive position against expanding threats from American and Chinese space enterprises. A senior European Space Agency executive stated Thursday that consolidation may be essential for European businesses to achieve the necessary size for global competition, though excessive concentration might restrict customer choices. These remarks were made as Airbus, Italy’s Leonardo, and France’s Thales pursue discussions about uniting their space-based operations.