02.12.09

Where was NORAD when it was needed?

Posted in Iridium at 2:57 pm by timfarrar

So now the unthinkable has happened, and two satellites have collided in orbit, despite the fact that NORAD is supposed to be tracking “more than 10,000 pieces of high-speed debris, some no larger than a football” and warning of potential collisions. Indeed to our knowledge, Iridium satellites have been moved in the past to avoid possible near-misses with debris.

As we said in the WSJ interview, the Pentagon are going to face a barrage of questions about exactly why there was no warning given about a possible collision: though you can’t predict that two satellites will definitely hit one another, unless Iridium had been maneuvering its satellite (which does not appear to be the case) it is easy to calculate when they may come within a few miles of one another a minimum of several days in advance.

Fortunately for Iridium, the disruption is reduced by the availability of in-orbit spares, and the fact that the satellite is only one out of 66 providing coverage, so there will just be a hole passing over any point on the Earth’s surface twice a day for 5-9 minutes (less at higher latitudes). Its a lot better than the failure of a GEO spacecraft which could eliminate service for months (or even years) across a large part of the globe, while a spare satellite is built and launched to replace it.

The main worry now is about how far the debris cloud will spread, and whether it will affect other Iridium satellites at that altitude, or even other satellites in nearby orbits. The closest commercial sytem is Orbcomm (only about 10km away), then there are optical imaging satellites a bit lower. The debris won’t get up to Globalstar’s orbit (600km further up) or of course the geostationary belt (36,000km above the earth). However, there are also a lot of government (military and civil) satellites in and around these orbits (including weather and other Earth observation satellites). In a worst case situation it is even possible that Iridium might have to raise the orbit of its remaining satellites slightly, but within reason this could probably be achieved without any additional service disruption.

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