Satellite Collision Risk Assessment: The Complete Guide for Operators

There are 14,368 active objects in orbit right now. Thousands more pieces of tracked debris. Every object is moving at 7+ km/s, and the catalog is growing faster than at any point in spaceflight history. If you operate a satellite — from a 3U CubeSat to a GEO communications bird — satellite collision risk is no longer a theoretical problem. It's a daily operational reality.

This guide explains what satellite collision risk assessment actually involves, how conjunction assessment (the formal process of identifying close approaches) works in practice, and what tools and services are available to help operators protect their assets — including open-source options like OrbitGuard.

What Is Satellite Collision Risk?

Satellite collision risk is the probability that two objects in orbit will come close enough to collide. "Close enough" is defined by a combination of miss distance, relative velocity, and uncertainty in both objects' positions.

The consequences of a collision at orbital velocities are catastrophic. At 11.55 km/s relative velocity — the speed at which some of the close approaches OrbitGuard detected on February 9, 2026 occurred — even a 1 cm fragment carries the kinetic energy of a hand grenade. A collision between two intact satellites generates thousands of trackable fragments and millions of smaller ones, each becoming a new collision threat.

This cascading effect is known as Kessler Syndrome, first described by NASA scientist Donald Kessler in 1978. It's the scenario where collisional debris generates more debris, potentially rendering entire orbital regimes unusable.

Why Conjunction Assessment Matters Now More Than Ever

Conjunction assessment is the process of screening orbital objects against each other to identify potential close approaches (called conjunctions). When a conjunction is found, operators assess the probability of collision (Pc) and decide whether to maneuver.

Several factors make this more urgent than ever:

• Mega-constellations: SpaceX alone operates over 6,000 Starlink satellites. Amazon's Kuiper, OneWeb, and others are adding thousands more. The number of potential conjunction pairs grows with the square of the number of objects.
• Limited maneuvering: Many satellites — including iconic assets like the Hubble Space Telescope — cannot maneuver at all. On February 9, 2026, OrbitGuard identified 3 close approaches between Hubble and Starlink satellites, the closest at just 6.2 km. Hubble has no propulsion system. It can only watch and hope.
• Cross-operator blindness: Unless operators actively share data, they have no visibility into what other satellites are doing. The 18th Space Defense Squadron's catalog on Space-Track.org helps, but TLEs (Two-Line Element sets) have inherent accuracy limitations.
• Debris from past events: The 2009 Iridium-Cosmos collision and various anti-satellite tests created debris clouds that still threaten operational satellites.

How Space Debris Tracking Works

Space debris tracking is the foundation of collision risk assessment. Without accurate tracking, you can't predict where objects will be — and you can't assess collision risk.

Ground-Based Radar and Optical Tracking

The U.S. Space Surveillance Network (SSN) operates a worldwide network of radar and optical sensors that track objects as small as 10 cm in low Earth orbit (LEO). The resulting catalog, maintained by the 18th Space Defense Squadron, contains orbital elements for over 27,000 objects.

The ESA Space Debris Office maintains independent tracking through its Space Surveillance and Tracking (SST) program, providing additional data for European operators.

Two-Line Element Sets (TLEs)

TLEs are the standard format for distributing orbital data. Each TLE describes an object's orbit using six Keplerian elements plus drag terms. They're propagated forward in time using the SGP4 (Simplified General Perturbations 4) algorithm.

TLEs have known accuracy limitations — typically 1-3 km position uncertainty at epoch, degrading rapidly over time. For detailed analysis of TLE accuracy and its impact on collision prediction, see our technical deep-dive.

Conjunction Data Messages (CDMs)

When the 18th Space Defense Squadron identifies a close approach, they issue a Conjunction Data Message (CDM) to affected operators. CDMs contain much more precise data than TLEs, including covariance matrices that describe position uncertainty.

However, CDMs have limitations. They're only generated for conjunctions the SSN identifies, they may arrive with limited lead time, and not all operators have access to the Space-Track.org system.

The Collision Risk Assessment Process

A complete satellite collision risk assessment follows these steps:

Step 1: Catalog Screening

Every active object is screened against every other tracked object to identify close approaches within some threshold distance. This is computationally intensive — with 14,368 active objects, there are over 103 million possible pairs to evaluate.

Step 2: Close Approach Filtering

Raw conjunction screening produces many false positives. Satellites in the same orbital plane that are intentionally co-located — like constellation satellites maintaining station — will always appear "close." OrbitGuard detected 174 co-located formations on February 9, 2026, and automatically filtered them to reduce noise.

Step 3: Probability of Collision (Pc) Calculation

For each genuine conjunction, the probability of collision is calculated. This typically involves:

• Projecting position uncertainties (covariance ellipsoids) of both objects onto the conjunction plane
• Integrating the probability of overlap given the combined hard-body radius
• The standard approach uses the Foster method or Alfano method for 2D probability integration

Thresholds vary by operator, but typically:

• Pc > 10⁻⁴ (1 in 10,000): Maneuver strongly recommended
• Pc > 10⁻⁵ (1 in 100,000): Elevated monitoring, maneuver considered
• Pc > 10⁻⁷: Flagged for awareness

Step 4: Maneuver Decision

If the Pc exceeds an operator's threshold, they must decide whether to maneuver. This involves weighing the collision risk against mission cost (fuel consumption, service interruption, and the risk of the maneuver itself potentially creating a new conjunction).

For satellites that can't maneuver — like Hubble, or university CubeSats without propulsion — all you can do is monitor and hope. This makes early warning even more critical. Read more about collision avoidance for small satellites →

Available Tools for Satellite Collision Risk Assessment

Government Services

• Space-Track.org: Free CDM and TLE data from the 18th Space Defense Squadron. Requires registration.
• ESA CREAM: ESA's Conjunction Risk Evaluation and Assessment Module, available to ESA-supported missions.
• NASA ODPO: The Orbital Debris Program Office provides environment models and assessment tools.

Commercial Services

Multiple commercial providers offer conjunction assessment as a service, with pricing typically ranging from a few hundred to thousands of dollars per satellite per month.

Open-Source Tools

OrbitGuard is an open-source collision screening tool released under the Apache 2.0 license. It performs full-catalog screening using SGP4 propagation and KD-tree spatial indexing, delivering results in seconds on consumer hardware.

For operators who want managed monitoring without running their own infrastructure, OrbitGuard also offers hosted plans starting at $199/month.

Building a Collision Risk Assessment Program

If you're an operator setting up collision risk assessment for the first time, here's what you need:

1. Register on Space-Track.org — get access to TLEs and CDMs for your objects
2. Establish screening thresholds — define what miss distances and Pc values trigger action
3. Set up automated screening — manual checking doesn't scale. Tools like OrbitGuard can screen the full catalog every few hours.
4. Define maneuver protocols — who decides, what's the lead time, what's the fuel budget?
5. Log everything — the UN COPUOS guidelines on long-term sustainability of space activities recommend maintaining records of all conjunction events and responses.

The Scale of the Problem: Real Numbers

To give you a sense of the scale: on a single day (February 9, 2026), OrbitGuard's screening of the active catalog found:

• 441 collision risks within standard screening thresholds
• 3 close approaches involving Hubble — a non-maneuverable national asset
• 174 co-located formations that needed filtering from raw results
• Relative velocities up to 11.55 km/s — far too fast for any last-second avoidance

This isn't a bad day. This is a typical day. Every day, hundreds of conjunction events occur. Most resolve safely due to the vastness of space. But the margins are shrinking.

What Comes Next

The space debris environment will continue to worsen before it improves. Active debris removal missions are years away from operational scale. New satellites are launching faster than old ones deorbit. The collision risk assessment tools and practices we build today will determine whether key orbital regimes remain usable for future generations.

If you operate satellites and don't yet have a collision screening program, now is the time to start. The tools exist — many are free. The cost of inaction is measured in lost missions, created debris, and a degraded orbital environment for everyone.

OrbitGuard is open source and free to run yourself. For managed monitoring, plans start at $199/month. View the source on GitHub →