When two satellites collide at 790 km above the Earth’s surface, who really cares which satellite “won”? It’s going to be a mess; chunks of metal and shards of solar panels exploding to life after their once-solid satellite structures impacted at a velocity of 11 km/s (that’s kilometres per second). Both satellites are losers, twisted, shattered remains of their former selves, cluttering Earth-orbit, causing all kinds of stress for other vehicles flying around in orbit.
However, when the Iridium communications satellite was hit by the defunct Russian Cosmos 2251 on February 10th, it turns out there was a “winner” in the satellite demolition derby (although I am using the word “winner” very loosely)…
On February 10th, something very rare happened: two satellites collided without warning. Not only was this unprecedented, it came as a huge surprise. Yes, space is getting rather busy, but space is also very big; huge volumes of the stuff separates the satellites whizzing overhead. Probably the best analogy is likening the satellite collision with intercepting a hypervelocity rifle bullet with another bullet. Very difficult, but it can be done given enough time and given enough bullets. As the numbers of satellites increase (the bullets) and time goes on, the likelihood of this happening was bound to increase, and in February, it did. Quite spectacularly.
However, NASA has been tracking the debris and noticed there aren’t as many fragments as they were expecting. Computer models suggest that during a direct collision between a 900 kg Cosmos and 560 kg Iridium, 1300 fragments should be produced. As of late-March, NASA has only tracked 823 pieces.
This means that the collision wasn’t a direct hit. “The Iridium is underrepresented,” said Mark Matney of NASA’s orbital debris programme. From Matney’s measurements, the reason why there are fewer bits from the Iridium satellite is that Cosmos 2251 was more compact. Looking at the designs of both, it becomes obvious that Iridium satellites have more appendages (antennae and solar panels), whereas the Cosmos has its solar panelling tiled around it’s bulbous body.
It looks like Cosmos 2251 probably hit a part of the operational communications satellite, leaving the bulk of Iridium intact. An impact at 11 km/s is still bad news however; if the Russian satellite hit anything it would have disintegrated on contact with any part of Iridium.
Although the Iridium satellite probably kept more of its mass intact, it was pretty much destroyed and it now orbits the Earth a lot smaller than it used to be. If that’s “winning” an orbital collision, I think I’d prefer to be pulverized like Cosmos 2251…
Source: New Scientist