A Close Shave: Recent Conjunction Illustrates Growing Collision Risk in Low Earth Orbit

LeoLabs Australia

On February 28, satellite operators and space safety experts breathed a collective sigh of relief. Once again, disaster was averted; but it was close.

At around 06:30 UTC, space situational awareness company LeoLabs, observed a conjunction at 608 kilometers between two non-maneuverable spacecraft: a derelict Russian satellite and an operational NASA satellite. The miss distance was less than 20 meters. (That’s about the size of a cricket pitch!)

There are several reasons why this event is significant — and concerning.

Figure SE1 Figure\* ARABIC 1: Leolabs' conjuction 3D visualization illustrates the close conjuction between the non-maneuverable satellites.

Very High Probability of Collision and Small Miss Distance

This is only the seventh time in two years that two intact, non-maneuverable objects had a conjunction of less than 20 meters. The small miss distance, with a combined hard body radius (CHBR) of ~11 meters, resulted in a probability of collision (PC) of 3.4%. This was the third largest PC value registered by LeoLabs since 1 January 2022 in LEO.

The small miss distance, especially in the radial direction, was concerning. This is the most important component of miss distance since two objects cannot collide if they are not at the same altitude.

Figure SEQ Figure \* ARABIC 2: The two spacecraft have comparable maximum "wingspans" of around 12m, but Cosmos 2221 is more substantial in all directions. The four large bottom panels on Cosmos 2221 are antennas used in its ELINT mission.

Satellites Had a Large Combined Mass

The combined mass of both satellites involved in the conjunction was around 2,550 kilograms. Why does mass matter? For every conjunction LeoLabs observes in LEO, the company compiles the risk using the following equation: risk = PC x mass involved. “Mass involved” serves as a surrogate for consequence as it is proportional to the number of fragments that would be produced if the two objects were to collide. LeoLabs’ analysis found that this event is tied for the second riskiest event in LEO over the last 26 months in large part due to the combined mass.

Collision Could’ve Added 50% More Debris in LEO

The resulting debris of a collision between these two objects, COSMOS 2221 and TIMED, would've created an increased collision risk on a large portion of LEO but especially on nearby lower orbits used by large constellations and human spaceflight.

Our analysis indicates that a collision would've resulted in ~2,000 to 7,500 cataloged fragments. This number is derived from analyzing the total mass, spacecraft construction, relative velocity, and encounter geometry. There are nearly 12,000 fragments in LEO as of 15 February. This one incident could've added 50% more debris.

The relative velocity of this event was around 14 km/s — that’s incredibly fast and is well above the six km/s threshold for a hypervelocity event. Hypervelocity events would most likely result in significant fragmentation of an object, even if it was merely “clipped” by another object.

If the two objects involved in this conjunction would’ve hit center-of-mass on center-of-mass, it could’ve created up to three times the objects’ combined mass (i.e., ~7,500 fragments). However, this was highly unlikely. The most likely event was that one of the object's solar arrays would’ve clipped the other object’s main body. In that case, one object would've been destroyed and the other damaged. (For example, if TIMED clipped COSMOS 2221, the total fragment count could've been ~2,500.)

How Can Dangerous Collisions Be Prevented?

First, this event illustrates the need for collision avoidance which requires frequent, high-quality measurements on all objects and activities in LEO. Commercial sensors, like LeoLabs’ global phased array radar network, are increasingly providing those measurements reliably and continuously. LeoLabs’ radars are linked through a computational engine that runs on cloud services. The company’s sites in Australia and New Zealand fill a historical coverage gap in the Southern Hemisphere critical to maintaining a 24/7, comprehensive view of LEO. This additional coverage has lowered the time between observations for objects and enabled greater data reliability, accuracy, and timeliness. Within minutes, data is collected from its sites and delivered as conjunction alerts to satellite operators using LeoSafe, LeoLabs’ collision avoidance service.

Second, this event illustrates the importance of advances in debris mitigation and debris remediation to combat the growing risk from derelict objects in LEO. LeoLabs, along with the Secure World Foundation, recently spearheaded a joint statement outlining the critical need to urgently remediate the massive derelict objects in LEO that pose the greatest debris-generating potential. Active debris removal (ADR) missions, like Astroscale’s ADRAS-J launched on 20 February 2024, are promising steps in the right direction.

A single collision in LEO could impact thousands of other satellites for decades. That’s why we must continue to work collaboratively and strategically to ensure this domain remains safe and secure for generations to come.

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