The European Science Foundation has signed a second agreement with Iridium LLC, the telecommunications satellite operator, providing a further degree of protection for an important radio astronomy band near to the Iridium operating frequency. Under the new agreement Iridium guarantees that unwanted interference from its flotilla of 66 low-earth orbiting satellites into the 1612 MHz radio astronomy band will be kept to acceptable levels for up to 50% of the time for the next six and half years.
This is the frequency used by astronomers to study the distribution of the hydroxyl radical, one of the most common interstellar molecules, enabling them to investigate a wide range of issues including the evaporation of comets and the birth and death of stars. The hydroxyl emissions come from regions that are hidden from optical telescopes by clouds of dust and gas and are billions of times weaker than the emissions from an Iridium satellite. Consequently, the small amount of power that leaks from an Iridium satellite transmitter outside of its assigned frequency band of 1621.3-1626.5 MHz is strong enough to drown out the faint cosmic emissions studied by radio astronomers.
Under a broader framework agreement signed by the ESF and Iridium in August of last year, Iridium has already pledged to ensure 24 hours a day of ‘unpolluted’ observation time from 1 January 2006. The new agreement covers interim arrangements until that date and provides a guarantee that Europe’s extensive and world-leading 1612 MHz research programmes will be able to continue albeit with a number of operating restrictions.
Led by Dr Titus Spoelstra, Frequency Manager of the ESF Committee on Radio Astronomy Frequencies (CRAF), Europe’s radio astronomers have won a number of additional concessions to similar agreements negotiated elsewhere in the world. The clear times during which interference levels are guaranteed to be low include not only overnight periods, but also weekends. These are particularly important to astronomers as they cover full 24-hour periods allowing them to study objects in any part of the accessible sky. Iridium has also agreed to make ‘quiet’ time available on request to cater for observations of spectacular or unusual events similar to the collision of Comet Shoemaker-Levy with Jupiter in July 1994.
However, while Europe’s radio astronomers have negotiated a better deal than many of their international counterparts, CRAF chairman Jim Cohen of the UK’s Jodrell Bank Observatory argues that the Iridium case has set a bad precedent in several respects, which could threaten the future development of radio astronomy. He points out that the allocation of the frequency band 1616-1626.5 MHz for space-to-earth transmissions was made by the International Telecommunications Union (ITU) before technical studies had been concluded on the possible harmful effects on radio astronomy. And while radio astronomy has been given regulatory protection by the ITU, in practice its measurements are now having to be squeezed into those times when Iridium can guarantee low interference levels. "In effect," says Cohen, "radio astronomy is time sharing with the radio waste of Iridium satellites. Given the explosive growth in satellite telecommunications and broadcasting, radio astronomers have to be worried about the long-term threat to their science from the unwanted emissions of all these satellites."
Eighty per cent of frequency bands allocated to radio astronomy on a primary basis are adjacent to a band allocated for space-to-Earth transmissions, although most have not yet been taken up. It is expected that the ITU’s World Radio Conference next year will for the first time set limits on unwanted emissions from satellites.
Further information and an updated list of cases of satellite interference to radio astronomy can be found on the web pages of the European Science Foundation’s Committee on Radio Astronomy Frequencies ESF-CRAF www.nfra.nl/craf
Head of Communication and Information, ESF
+33 (0)3 88 76 71 32
Dr Jim Cohen
Chairman of the ESF Committee on Radio Astronomy Frequencies (CRAF), Jodrell Bank Observatory, UK
+44 1477 571321
Dr Titus Spoelstra
Frequency Manager, CRAF, PO Box 2, 7990 AA Dwingeloo, the Netherlands,
+31 521 595100
Notes for editors:
1. The European Science Foundation is the European association of 65 major national funding agencies devoted to scientific research in 22 countries. The ESF assists its member organisations in two main ways: by bringing scientists together in its scientific programmes, networks, exploratory workshops and European research conferences, to work on topics of common concern, and through the joint study of issues of strategic importance in European science policy.
2. The ESF Committee on Radio Astronomy Frequencies (CRAF) was established in 1988 to coordinate the European efforts for the protection of radiospectrum bands used by the Radio Astronomy Service and other passive applications.
3. The criteria defining detrimental levels of interference for radio astronomy in the 1610.6-1613.8 MHz band have been set by the International Telecommunications Union (ITU-R RA769-1) at –238 dB (Wm-2Hz-1). Even this represents a significant concession by radioastronomers to satellite-enabled industries as current state-of-the-art sensitivities would imply that these should be several orders of magnitude more stringent.
4. Further reading: The CRAF Handbook for Radio Astronomy – second edition (1997), published by the ESF, ISBN: 2-903148-94-5.
For further information contact : Andrew Smith
Category: Media Centre, Press Releases 1999