Weightlessness. German astronaut Ulrich Walter demonstrates the weightless conditions of orbit inside the Spacelab D2 laboratory module. Spacelab D2 was carried into orbit on Shuttle Mission STS- 55 of 26 April to 6 May 1993. The module contained equipment for 90 experiments, most of which were provided by the German Space Agency (DARA) and the European Space Agency (ESA). The experiments covered topics in physics and in life and materials sciences. Two German astronauts joined five Americans to form the crew for the flight.