Introduction to Frequency Management
Transmission of science data from or to a spacecraft generally requires a transmitter and a receiver which need to be coordinated with other users in several respects. Objects transmitting or receiving data via electromagnetic waves are referred to as stations in the international Radio Regulations (RR). The RR are published and generally updated every few years by the International Telecommunications Union (ITU) which is a specialised organisation of the United Nations (UN). Stations typically used by space agencies may be located on Earth, in space or on celestial bodies.
In order to establish a radio frequency link for data transmissions between an object in space, usually a satellite, and another station, typically an Earth station, suitable frequencies and a minimum bandwidth are required. These are also regulated in the RR by means of frequency allocations. They need to be coordinated with other potential users of the relevant allocations and possibly also with other affected users of neighbouring bands. An exception are passive bands, as they contain only receiving stations, generally quite susceptibel to interference.
When a mission is in the planning stage, suitable frequencies are selected depending on the available frequency allocations.
Several bands are allocated to Space Science Services (SRS) and Earth Exploration Satellte Service (EESS). For the operation of the satellites, there exists also a Space Operation Service (SOS). Depending on the amount of data to be transmitted and requirements for safe contact with the spacecraft, suitable candidates are picked for further assessment. These are generally coordinated first among space agencies by means of bi-lateral or sometimes multi-lateral meetings. A small number of major space agencies formed the Space Frequency Coordination Group (SFCG) some 40 years ago. Today, most active space agencies are members of this group which plays an important role in global coordination of frequency plans, optimum use of available resources and interference avoidance techniques. The SFCG meets once per year and has been a driving force for decades in successfully defending the interest of space agencies in the ITU.