Maurer applied to the European Space Agency as an astronaut in 2008, but was not initially appointed to the European Astronaut Corps. He formally joined the European Astronaut Corps in July 2015. In March 2018, he gained certification to perform International Space Station-related spacewalks in the American spacesuit EMU. In 2018 he also successfully graduated from both basic astronaut training and pre-assignment training and thus became fully certified to go to space. On 28 July 2020, Maurer was announced as a backup for Thomas Pesquet for the ISS expedition 65. His own flight is scheduled to take place no earlier than September 2021 aboard SpaceX Crew-3.
The European Space Agency is an intergovernmental organisation of 22 member states. Established in 1975 and headquartered in Paris, France, ESA has a worldwide staff of about 2,000 employees. ESA's space flight programme includes human spaceflight (mainly through participation in the International Space Station program); the launch and operation of unmanned exploration missions to other planets and the Moon; Earth observation, science and telecommunication; designing launch vehicles; and maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana.