Scientific Use of Radio - Challenges from Space

Astronomy, several geophysical sciences including meteorology, and various remote sensing sciences use radio receivers to register extremely weak natural radio radiation from a multitude of objects and media. The sensitivity requirements of all these sciences, and in particular radio astronomy, make them very vulnerable to interference from man-made radio signals. Even out- of-band emission from active radio services in nearby frequency bands could be harmful to a passive scientific radio service. As long as the interfering radio transmitters are ground-based, geographic coordination could solve the problem, in principle. In recent years, however, many satellite-borne radio services have been defined, using low polar orbits. Such satellites cover the entire surface of the Earth in a short time and therefore no place is geographically protected from interference. Due to the increasing congestion in the radio spectrum, several satellite services have been allocated in frequency bands adjacent to or close to bands allocated to the radio astronomy service. There still is a danger that many future satellite services will be allocated in bands close to radio astronomy bands. Examples of such cases are given.