The International Space Station (ISS) is the largest technical vehicle ever built by mankind. It provides a living area for six astronauts and also represents a laboratory in which scientific experiments are conducted in an extraordinary environment. The deployed sensor technology contributes significantly to the operational and scientific success of the station. The sensors on board the ISS can be thereby classified into two categories which differ significantly in their key features: (1) sensors related to crew and station health, and (2) sensors to provide specific measurements in research facilities. The operation of the station requires robust, long-term stable and reliable sensors, since they assure the survival of the astronauts and the intactness of the station. Recently, a wireless sensor network for measuring environmental parameters like temperature, pressure, and humidity was established and its function could be successfully verified over several months. Such a network enhances the operational reliability and stability for monitoring these critical parameters compared to single sensors. The sensors which are implemented into the research facilities have to fulfil other objectives. The high performance of the scientific experiments that are conducted in different research facilities on-board demands the perfect embedding of the sensor in the respective instrumental setup which forms the complete measurement chain. It is shown that the performance of the single sensor alone does not determine the success of the measurement task; moreover, the synergy between different sensors and actuators as well as appropriate sample taking, followed by an appropriate sample preparation play an essential role. The application in a space environment adds additional challenges to the sensor technology, for example the necessity for miniaturisation, automation, reliability, and long-term operation. An alternative is the repetitive calibration of the sensors. This approach, however, increases the operational overhead significantly. But meeting especially these requirements offers unique opportunities for testing these sensor technologies in harsh and dedicated environments which are not available on Earth, therefore pushing the related technologies and methodologies to their limits. The scientific objectives for selected experiments, representing a wide range of research fields, are presented, including the instrument setups and the implemented sensor technologies, and where available, the first scientific results are presented.
