Computer analysis of the orbits of both satellites prior to impact show that they were almost at right angles to each other and impacted at a velocity of 11 kilometers per second. Preliminary assessment shows that the orbital decay time for much of the debris field will be decades, proving a significant risk to existing and future LEO satellites. Over 800 significant pieces of debris from this incident are being tracked from Earth.

Possibly the most prone spacecraft is the constellation of Iridium satellites. In February 2009 there were 70 satellites in the constellation orbiting at approximately 800Km above Earth. To quote NASA:

” Whizzing through the Iridium satellite altitude regime many times per day are approximately 3300 catalogued objects.

Close approaches between these objects and iridium spacecraft are common occurrences”.

As can be seen from these two drawings (taken from NASA’s Orbital Debris Report V13 I2) the debris field is predicted to spread significantly in the 6 months immediately after the incident,  increasing the threat to Low Earth Orbit satellites.

Apart from the 830 or so larger catalogued pieces of debris, many hundreds more are being tracked by the US based X band Haystack radar, which can detect objects down to 1 cm in diameter.

Prior to the  collision of Iriduim 33 and Cosmos 2251, there had only been 2 collisions in space, generating minimal debris.