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News | Nov. 15, 2023

Navigating the Orbital Racetrack: How the 18th Space Defense Squadron Finds and Tracks Debris

By Julian Labit

Imagine you're a racecar driver hurtling along a crowded track, surrounded by hundreds of other vehicles. They're in front, behind, and beside you, weaving through the lanes at breakneck speed. Some are even traveling towards you, whizzing past with just inches to spare. This is the reality of our space environment today, where satellites are constantly maneuvering and orbiting our planet, dodging debris and other spacecraft as they go. And as global space operations continue to increase, so too will the risk of close calls and collisions. 

New satellites launched into space increase the likelihood of debris generated from these objects, turning usable orbits into a hazardous racetrack. Just like a pileup on a busy racetrack, space debris could collide into other satellites, disrupting critical communication, navigation, and weather forecasting services. 

The 18th Space Defense Squadron, a unit within the U.S. Space Force’s Space Delta 2 – Space Domain Awareness and Space Battle Management, plays a crucial role in keeping tabs on this ever-expanding orbital racetrack. Acting as the lighthouse of space, 18 SDS is responsible for monitoring and tracking all artificial objects in Earth’s orbit to ensure the safety of our satellites, astronauts, and space exploration endeavors. 

One of the biggest challenges the 18 SDS faces is fragmentation. Resident space object fragmentation refers to the separation of artificial object in space, creating smaller pieces of debris. This can happen for various reasons, including intentional destruction, collisions, or natural wear and tear. When a satellite fragments, it can create thousands of pieces of debris, each posing a collision risk to other objects in space. Here are four main types of RSO fragmentation (a fragmentation event can fall into multiple categories): 

  1. Anomalous Debris-Causing Event: This occurs when a satellite releases debris due to factors such as corrosion or fatigue These fragments typically spread at relatively low speeds and remain close to the satellite's orbit. The amount of debris generated is generally limited, and the satellite itself usually maintains its functionality. 

  1. Breakup: This is a more severe fragmentation event that generates a relatively large number of debris fragments that spread at a high velocity far from the satellite’s orbit. Breakups can be intentional or unintentional. Unintentional breakups can include explosions of tanks caused by residual fuel or volatile chemicals. Intentional breakups include direct-ascent anti-satellite missile tests. This is exactly what happened when a Russian DA-ASAT missile destroyed the Cosmos 1408 satellite in an anti-satellite weapon test in 2021, generating a massive cloud of debris of over 1,700 trackable pieces that threatened the International Space Station, the Tiangong space station, their respective inhabitants and other active spacecraft. Cosmos 1408 debris continues to pose a threat to humans in space and artificial space objects to this day. 

  1. Collision: This occurs when two or more objects in space collide, creating debris. A notable example is the Iridium-Cosmos collision, which was a non-intentional collision between a defunct Russian military satellite Cosmos 2251 and an active commercial Iridium 33 satellite in February 2009. This was the first significant collision of two artificial satellites in space, generating a massive cloud of debris. The collision created approximately 1,500 pieces of debris larger than 10 centimeters in diameter, posing a significant risk to satellites and on-going space operations. As a result, the ISS was forced to maneuver to avoid potential collisions with the debris. 

  1. Mission-Related: This involves debris released from a satellite during normal operations, such as the deployment of a payload. For instance, unintentional separation of non-payload components can occur when payloads deploy from a spacecraft bus. 

RSO fragmentation poses a significant threat to space operations. Debris travels at orbital speeds and can damage or destroy satellites, and the risk of collision increases as more objects orbit Earth. 

The 18 SDS uses a variety of tools and techniques to monitor and identify fragmentation events and debris. They start by analyzing data from the Space Surveillance Network, a network of ground-based and space-based sensors that continuously monitor the space environment. 

One way the 18 SDS predicts fragmentations is by tracking changes in orbital parameters, which can indicate if a satellite is releasing gas or undergoing structural stress. They also use clustering algorithms to group objects with similar properties, such as size, shape, and orbital path, to identify potential fragmentation debris. 

When a fragmentation occurs, the 18 SDS springs into action, tasking phased array sensors to collect debris observations as uncorrelated tracks—a short track segment (usually formed from a set of observations taken over a short period from a single radar sensor) that is not associated or correlated with any existing orbit. UCT processing—correlating observations to be identified as a single object—is a manually intensive process that can take long periods of time to accomplish; however, doing so allows 18 SDS to identify the fragmentation and track the pieces of debris. 

Determining the time and cause of a fragmentation is crucial for understanding the risks posed by debris. The 18 SDS uses specialized software to analyze debris trajectories, identify fragmentation locations, and look for signs of explosions or collisions to determine the cause of the fragmentation. 

Finding the parent object, or the original satellite that fragmented, is another important task for the 18 SDS. This involves analyzing radar data and other observations to identify the largest piece of debris. 

Once the debris has been identified, the 18 SDS incorporates it into routine conjunction assessment processes. This means the orbital paths of spacecraft are continuously monitored and used to identify potential collision risks. This information is then shared with other military and commercial space agencies and organizations through, U.S. Space Command’s public website that maintains the most complete satellite catalog of Earth-orbiting artificial objects. Coordination and collaboration with satellite owner-operators can be extremely helpful during fragmentation events, as they can provide valuable information about operability of their satellites or whether the separation event was intentional or not. 

The efforts of the 18 SDS are guided by the Department of Defense's Tenets of Responsible Behavior in Space, which emphasize operating in space with due regard for others, limiting debris generation, and communicating effectively ensuring the safety of our satellites, astronauts, and space exploration endeavors. By mapping out the space terrain, the 18 SDS helps space users safely navigate the orbital racetrack. 

To learn more about the objects currently on the 18 SDS’s radar, visit