An important radio astronomy frequency band is to be protected in Europe from satellite interference. The telecommunications satellite operator, Iridium LLC, has signed an agreement with the European Science Foundation's Committee on Radio Astronomy Frequencies (CRAF) to reduce emissions from Iridium's flotilla of 66 low-earth orbiting satellites. Astronomers were worried that signals from the satellites would seep into 1612 Megahertz waveband, a region sensitive to radiation produced by hydroxyl radicals, one of the most common interstellar molecules.
Signals produced by the satellites are over a 100 times stronger than the radio sources studied by astronomers. Under the new agreement, European radio astronomers will get 24 hours of ‘unpolluted’ observation time from 1 January 2006. However, they will have to negotiate for ‘restricted’ observation times with Iridium until that date. The CRAF has also agreed to help to try and find ways of improving Iridium’s satellite transmissions to reduce leakage from the network.
Earlier this year, the Arecibo radio telescope in Puerto Rico signed a separate time- sharing agreement with Iridium, which was seen by many in the radio astronomy community as too favourable to the company. European governments, on the other hand, refused to grant operating licences to Iridium – which goes operational next month – until they had reached an agreement with the CRAF.
Despite this agreement, interference from satellites remains an increasing threat to astronomy. “This is not an isolated problem, ” says Jim Cohen, chairman of CRAF. “The number of cases of interference to radio astronomy from satellites is growing steadily. Unless the protection of radio astronomy is taken into account early in the design of new satellite systems, our science could face a difficult future.”