Cosmos 2251

Launch data:

Decay:

Mission details:

• On Feb 10, 2009 Cosmos 2251 and Iridium 33 (1997-051C) collided. It was the first collition between 2 satellites in orbit.
• As of Mars 10, 2009, there were 454 debris objects from the collision with Iridium-33 in the catalog.

COLLISION BETWEEN COSMOS 2251 (1993-036A/22675) AND IRIDIUM 33 (1997-051C/24946):

• On February 10th Cosmos 2251 and Iridium 33 collided : the time of the collision – as estimated from the pre-collision Two-Line Orbital Elements and using the SATRAK “COMBO” module – was 16:56 UT.
• The pre-and post- collision orbital data for the two satellites are as follows:

  Cosmos 2251	Feb  9.50   74.04 deg   100.619 minutes   776 km   799 km    99 deg
  		Feb 12.08   74.04 deg   100.555 minutes   767 km   803 km   157 deg
  
  
  Iridium 33	Feb  9.78   86.40 deg   100.403 minutes   776 km   779 km    85 deg
  		Feb 12.16   86.39 deg   100.525 minutes   776 km   791 km    81 deg
  

  The tacit assumption is made that the post-collision element sets relate to the remaining bodies of the two satellites – this may not be correct.
  
  
• The left-hand graph above shows the locations of Cosmos 2251 and Iridium 33 between 16:46-17:06 UT on February 10th. From the Two-Line Element Sets the closest approach between the two satellites was at 16:56:00 (time resolution 6 seconds) when they were over 72.50 deg N, 97.99 deg E: Cosmos 2251 was just starting to travel in a south-easterly direction while Iridium 33 was travelling in a north-easterly direction. The right-hand graph shows the variation in the distance between the two satellites between 15:00-19:00 UT on February 10th. (note that the distance scale is logarithmic): the calculated minimum distance between the satellites is about 2 km, although the true minimum distance was – of course – less than this.
  
• Reports from the United States suggest that there might be a debris cloud of ~600 objects following the collision.
  There is the question of “who is to blame?” for the collision. According to Russian statements, Cosmos 2251 had not been operating since the mid-1990s and it is known that this class of satellite – Strela-2 – did not carry any in orbit manoeuvring system. On the other hand, Iridium 33 was a fully-functioning satellite and carried its own propulsion system: the Iridium satellites use the propulsion system to manoeuvre to and from the operational Iridium orbital regime as well as relocating the satellites within the constellation. Therefore, Iridium 33 was apparently capable of performing a small manoeuvre to prevent the collision with Cosmos 2251.
• The Iridium satellite spanned about 5 meters across its solar arrays. Strela-2M used gravity gradient stabilization, and probably spanned 17 meters including the gravity boom. When calculating collision probabilities, it's important to remember that booms and antennae mean that many satellites have much larger cross-sections than the size of their main body would imply.