Iridium 33/Cosmos 2251 Collision

Coverage started 2009 March 5

Updated 2009 March 11

In the report issued on 2009 February 10 at 1502 UTC, SOCRATES predicted a close approach of 584 m between Iridium 33 and Cosmos 2251. This was not the top predicted close approach for that report or even the top predicted close approach for any of the Iridium satellites for the coming week. But, at the time of predicted close approach, Iridium 33 suddenly went silent. The US Space Surveillance Network (SSN) subsequently reported that they were tracking debris clouds in both the Iridium 33 and Cosmos 2251 orbits, confirming a collision.

This is the first time two satellites are known to have collided on orbit. While Cosmos 2251, a Russian communications satellite, is thought to have ceased operations about two years after it was launched in 1993, Iridium 33 was part of the operational Iridium constellation of 66 satellites at the time of the collision.

As of today, the SSN is tracking 217 pieces of debris associated with Iridium 33 and 457 pieces of debris associated with Cosmos 2251. The materials below are provided to give a sense of the current relationship between the Iridium constellation and the resulting debris clouds.

Click for larger image

Screen shot from AGI Viewer file of current Iridium constellation and collision debris clouds

Download Current Iridium Constellation Scenario

The graphic above shows the current Iridium constellation with the orbits for the operational satellites shown in green, the spares shown in blue, and the inactive satellites shown in red. The Iridium 33 debris is shown in yellow and the Cosmos 2251 debris is shown in orange. An AGI Viewer file (see bottom of this page for more information on AGI Viewer) of the event is also available.

Gabbard plots of the two debris clouds show the relative distribution of the debris in altitude and suggest that more of the Iridium 33 debris went to slightly higher orbits while much of the Cosmos 2251 debris went to lower orbits, with some of it already reentering the Earth's atmosphere.

Click for larger image

Gabbard Plot of Iridium 33 Debris Cloud

Click for larger image

Gabbard Plot of Cosmos 2251 Debris Cloud

Together with a 3D interactive plot of the relative velocities at the time of the collision (coming soon), these Gabbard plots should help develop a better understanding of the actual collision geometry.

Note: Larger versions of all the images provided on this page are available by clicking the images. The interactive AGI Viewer files of these scenes are also provided to give you a far better sense of the overall environment by allowing you to zoom in and out and move around the Earth while watching all the satellites moving in their orbits.

In the coming days, I will be providing additional analysis showing:

  • The event at the time of collision
  • The relative velocity spread of the initial debris
  • A summary of that week's SOCRATES reports showing where this event was ranked and discussing the implications

Note: AGI Viewer is a free product which allows anyone with a Windows computer to view an STK (Satellite Tool Kit) scenario. With it, you can animate a scenario forward or backward, pause the animation, and zoom or pan the view for a more complete understanding of the event. Just like with Adobe Acrobat, where the authoring software requires a license but the Adobe Reader is free, STK can produce AGI Viewer files—also known as VDFs—which can then be viewed by anyone with the AGI Viewer software. You can find the free AGI Viewer on the AGI web site at (download here if you are experiencing problems with the AGI site).

Note: My ongoing support to Iridium and the Joint Space Operations Center on this event since February 10 has necessarily taken priority over some of my additional duties operating CelesTrak and has subsequently delayed this report. As the situation continues to evolve and more data becomes available to the public, I will continue to update the information provided here, along with providing additional analysis. —T.S.

TLE Data Space Data
Space Weather
SATCAT Columns
Boxscore Software
Dr. T.S. Kelso []
Last updated: 2009 March 11 15:34:35 UTC
Accessed 1,001 times since 2000 December 16
Current system time: 2009 March 17 04:37:27 UTC