Sleeping satellites — Iridium 33 and Kosmos 2251 collide
There are more than enough bits of space junk in orbit around our planet, ranging from defunct satellites to, at one point last November, a NASA astronaut’s toolkit. For the most part they’re no threat to us down here on the surface, as all but the largest tend to disintegrate on re-entry into the earth’s atmosphere, but they are something of a risk to space stations and vehicles like the shuttle.
The good news is, then, that since Tuesday there have been two fewer large orbiting objects – a result of a high-speed collision between two communication satellites. The bad news is that said two objects have been reduced to several hundred smaller ones, the number and path of which nobody is yet able to predict.
The explosive smash happened 485 miles above the earth’s surface, when a live US satellite and a decommissioned Russian one crossed paths over Siberia.
It’s hard to grasp just how unlikely such a collision is, and how hard the two must have hit each other. Satellites in a low-earth orbit (LEO), as both Iridium 33 and Kosmos 2251 were, are subject to almost the same gravity as they would be on the planet’s surface, so they need to travel at huge speeds to avoid simply being claimed by the earth.
Really huge speeds: a typical LEO orbital velocity is above 17,000 miles per hour, or more than 30 times the speed of an airliner. While the two satellites might not have hit each other head on, even the most gentle of nudges would have seen them close on each other at a daunting rate. A head-on smash would have brought them together at more than nine miles per second.
Trying to work out the amount of energy involved in that kind of crash makes me want to lie down in a dark room. The BBC says that Iridium 33 weighed 560kg and that Kosmos 2251 tipped the scales at 950kg. Some rough calculations tell me that smashing the two satellites together could release as much energy as exploding 22 tonnes of TNT.
Which makes the BBC’s animated reconstruction seem just a little quaint.
IMAGE by Flickr user Mulad
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Originally posted 2009-02-12 17:24:00. Republished by Blog Post Promoter
