COLLISIONS IN ORBIT POSE A SERIOUS THREAT TO SATELLITES AND SPACECRAFT. BUT EVEN IF
THEY CAN BE PREDICTED, IT COULD BE IMPOSSIBLE TO PREVENT THEM.
■ FEATURE ARTICLE
On February 10, 2009, two communications satellites— Cosmos 2251 and Iridium 33—collided catastrophically in Earth orbit, 789 kilometers above northern Siberia. The event was not entirely a surprise: Many observers had recorded and tracked noticeably close approaches between the pair. However, in terms of both the minimum distance between
the satellites and the complicated calculations that predict the probability of collision, these satellites were not considered particularly at high risk. Among all the known close-approaching satellites, these two were hardly even in the top 200. Yet, they collided. Both Cosmos 2251 and Iridium 33.