Ask Dr. SETI ®
Do you know how much the Iridium satellites will influence the amateur radio astronomy and SETI? I've learned that some radio observatories (in the north hemisphere) had signed agreements with Motorola. But, what will happen with those who work in the south, especially with the amateurs?
The Doctor Responds:
Even though Iridium does not actually violate the International Telecommunications Union allocations, It is entirely possible that radio astronomy activities around that frequency will be impacted by adjacent-channel interference. The agreement to which you refer was reached between the European Science Foundation (ESF) and Iridium LLC, operators of the Motorola satellites. A press release issued by ESF on 13 August 1998 states:
The agreement signed by the ESF, on behalf of its associated Committee on Radio Astronomy Frequencies (CRAF), and Iridium LLC is the result of six months of intense negotiations. Under its terms, Iridium guarantees Europe's radio astronomers 24 hours a day of 'unpolluted' observation time from 1 January 2006. Both parties are also committed to reaching a further agreement by 1 March 1999 on transitional arrangements, covering the number of hours each day, during which Iridium unwanted emissions are to be restricted and an agreed maximum interference level at other times, for the period 1 March 1999 to 31 December 2005. For the six months from Iridium's start-up in September 1998 until 1 March 1999, the satellite company has agreed to keep emission levels below harmful interference levels as requested by the radio astronomers. However, in practice, even these levels imply a concession by radio astronomers to satellite-enabled services as the sensitivity of current state-of-the art radio astronomy equipment would imply that they should be set considerably lower.
Although this agreement appears to provide some relief to European radio astronomers, I see no such protection being proposed for the rest of the world. Satellite interference is not new to the SETI community. Radiation at 1575 MHz from the constellation of 24 Global Positioning System (GPS) satellites is a well known pollutant in the water-hole spectrum. Fortunately, observations around the 1420 MHz hydrogen line, and the hydroxyl component around 1660 MHz, should not be affected by Iridium. As those are the two most popular frequencies for SETI, the impact on our own Project Argus search should be tolerable. However, Iridium is only the beginning, and other, competing PCS satellite constellations are planned. Things can only get worse.
As of the third quarter of 2000, the Iridium commercial venture has gone bankrupt, and the satellites are scheduled to be de-orbited (i.e., burned up in the Earth's atmosphere) over a two-year period. I suppose this is good news for radio astronomy and SETI, and bad news for Iridium's investors. Yet, despite Iridium posting a $5 Billion loss, other constellations of low Earth orbit personal communications satellites are planned, and many of them propose to operate in or near the prime radio astronomy bands. So Iridium is simply Round One of an ongoing battle between science and commerce.
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this page last updated 28 December 2002
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