Iridium: The Story

As you read this, the Iridium satellite communications system is shutting down. This event is not being mourned by radio astronomers. Here's why. Three years ago, astronomers at DRAO were rather taken aback by the arrival of a high-powered team of negotiators representing Iridium, a company in the process of setting up a global cellular communication system using 66 satellites in low Earth orbit. They wanted us to sign a "Memorandum of Understanding" accepting levels of inteference in the 1610-1613MHz OH band that would deny us its use for 75% of the time. All this was despite the 1610-1613MHz band being allocated by international agreement to radio astronomy as a primary user. At the same time, Iridium teams were hitting radio observatories all over the world. Some observatories were forced to sign by their parent administrations, who had also been lobbied. We signed no such agreement. We believe that if there are international regulations dictating the level of protection for radio astronomy, we should not sign local agreements agreeing to their contravention. It's like motorists agreeing among themselves to raise the speed limit.

We now have a good idea of what was behind all this. The Iridium company had only a certain amount of money to spend on its satellite system. This dictated how much each satellite could weigh, how much power it could generate, and hence the power available to the transmitter. It was marginal. To optimize antenna sensitivity and the use of transmitter power, they devised an antenna system made up of active elements, each with its own power amplifier. In that way a beam could be generated to illuminate only the required area. Unfortunately the Iridium company decided that no spare power, weight or money was available for adequately filtering the outputs of the many amplifiers to prevent their intermodulation products from obliterating the nearby radio astronomy band. Instead, they concentrated on persuading radio astronomers around the world to sign agreements accepting the interference. The lobbying was heavy and at all levels. It was in Geneva and in national capitals. They had a very tough lobbyist working in Ottawa.

Fortunately, their system was the wrong product at the wrong time, and technically inadequate. The rapidly-expanding cellular phone system left little demand for Iridium systems other than in the sparsely-populated areas of the world, where there are few customers. The transmitter power proved too low, and the system only worked well when users were in line of sight with the satellites. In buildings, cars and in city cores the service was less reliable. Iridium failed to attract enough customers and the company went bankrupt.

Astronomers are not against new communication technologies. They have revolutioned both the power of our science and how we do it. However, we are strongly in favour of engineering responsibility and recognition of hard-won international agreements. As new radio services are implemented systems, and develop radio telescope systems orders of magnitude more sensitive than currently attainable, users of the radio spectrum will be forced to work together in a responsible fashion. We are trying very hard to do our part. One dragon has gone. However, there are still suspiciously large things moving around in the bushes. It isn't over yet.

Ken Tapping      <Ken.Tapping@hia.nrc.ca> Ken was born in Erith, Kent, UK. He started in radio astronomy while at high school by building radio telescopes and doing radio astronomy from parents' back yard. Then, with the help of a BSc in mathematics from the University of London, an MSc in Space Science from University College (London) and a PhD from the University of Utrecht (The Netherlands), he found he could do radio astronomy and get paid for it. He first worked with the Science Research Council (UK), got involved in VLBI experiments with NRC, and moved to the other end of the baseline in 1975. He is interested in solar physics, inherited the Solar Flux Monitoring Programme in 1985, and moved with the programme to DRAO in 1990.

Frequency Protection    New Opportunities    Contents

CASSIOPEIA -- 2000-ME