Satellites hit with 'unidentified interference'

Satellites hit with 'unidentified interference'
European, Middle East, African television stations affected

Mysterious source jams satellite communications

Paris-based satellite company Eutelsat is investigating "unidentified interference" with its satellite broadcast services that temporarily knocked out several television and radio stations. The company declined to say whether it thought the interference was accidental or deliberate.

The problem began Tuesday afternoon, blocking several European, Middle East and northeast African radio and television stations, as well as Agence France-Presse's news service. All transferred their satellite transmissions to another frequency to resume operations.

Theresa Hitchens of the Center for Defense Information think-tank in Washington DC, US, says there have been cases of deliberate satellite jamming in the past, but it is hard to see what motivation there would be in this instance.

"It's really puzzling to me," she told New Scientist. "If it was accidental, why would they be so secretive about saying what the source was and if it's deliberate, you've got to wonder why – it just seems to me to be an odd target, unless someone's ticked off at the French," she says.

Hitchens points out that there have been cases of deliberate jamming, including one in the 1990s when Indonesia and Tonga had a dispute over which country had the rights to a particular satellite orbital slot. Tonga had leased the slot to a satellite firm based in Hong Kong, but Indonesia had its own satellite in the same slot and proceeded to jam the Hong Kong satellite.

In a more recent incident, the US claimed in 2003 that Cuba was jamming its satellite broadcasts into Iran.

There are a variety of ways to interfere with a satellite's communications. One is to broadcast a stronger signal, either from the ground or from another satellite, that drowns what the satellite is sending to the ground, preventing people from receiving its signal. Another is to blast a signal at the satellite itself so that it cannot hear what the ground is trying to tell it.

Communications satellites act like conduits, listening to the ground and re-broadcasting what they hear. If someone drowns out the uplink signal with noise, then the satellite will re-broadcast the noise instead of the intended television or radio program.

Military satellites use methods like encryption and frequency hopping to prevent jamming, but many commercial communications satellites lack such safeguards, Hitchens says. "Given the fact that militaries increasingly rely on commercial satellites for communication, this has generated a lot of discussion," she says.

A 2004 report of the satellite task force of the US President's National Security Telecommunications Advisory Committee highlighted potential jamming of satellites as a key concern.

Richard DalBello, vice-president of government affairs for satellite operator Intelsat General says accidental interference occurs all the time. Intelsat deals with thousands of such events each year, he says. The equipment at ground stations used to communicate with satellites can malfunction, interfering with other people's efforts to communicate with the same satellite, he says.

Given this, the fact that Eutelsat does not know the source of the interference yet is "really not indicative of anything nefarious", he says. "Obviously if something persists or as you move traffic [to other satellites] it follows you, there are some things that give you pretty clear clues," he adds.

Deliberate interference may be more common than is widely recognised, however. The website of the Satellite Users Interference Reduction Group, whose members include Intelsat and other industry players, lists 11 incidents of deliberate interference with satellite communication since January 2005, although this comprises only 0.7% of the total transmissions.