Conjunction Assessment Explained: How Operators Handle Close-Approach Alerts

When two objects in orbit are predicted to pass dangerously close, that event is called a conjunction — and the process of evaluating it is conjunction assessment (CA). It's the analytical core of collision avoidance: the work of deciding whether a predicted close approach is a genuine threat worth spending fuel on, or noise you can safely watch and clear.

This article walks through what conjunction assessment actually involves, how to read the alert that drives it, and the factors that turn a warning into a maneuver.

New to the topic? Start with our guide to satellite collision avoidance, then come back here for the decision-making detail.

What conjunction assessment is

Conjunction assessment is the ongoing process of:

1. Predicting where your satellite will be,
2. Screening that path against every other tracked object,
3. Quantifying the risk of any predicted close approach, and
4. Deciding whether — and how — to respond.

It is fundamentally a problem of uncertainty. We never know an object's future position exactly; we know a region it will probably occupy. Conjunction assessment is about reasoning carefully about overlapping regions of uncertainty, not just two dots on a map.

Reading a Conjunction Data Message (CDM)

The alert that drives the whole process is the Conjunction Data Message (CDM). A CDM is a standardized report, and the fields that matter most are:

• Time of Closest Approach (TCA) — when the two objects will be nearest. This sets your decision deadline.
• Miss distance — the predicted smallest separation, usually split into radial, in-track, and cross-track components.
• Probability of collision (Pc) — the modeled likelihood of an actual hit, accounting for object sizes and position uncertainty.
• Covariance — the uncertainty in each object's predicted position. Large covariance means a fuzzy prediction.

You will often receive multiple CDMs for the same conjunction as new tracking data arrives. The story they tell over time — is Pc climbing or falling as uncertainty shrinks? — matters more than any single snapshot.

The three factors behind every maneuver decision

1. Probability of collision vs. your action threshold

Most operators set a threshold — commonly around 1 in 10,000 (1e-4) — above which they consider a maneuver. But Pc alone is misleading: a low Pc with high uncertainty can be more dangerous than a moderate Pc that is well-characterized, because the risk may simply be hidden inside a fuzzy prediction.

2. How uncertainty is evolving

A good conjunction assessment tracks how the prediction sharpens as TCA approaches. Sometimes waiting for one more CDM resolves a scary-looking event without spending any fuel. Sometimes waiting is exactly the wrong call. Knowing which is the skill.

3. The cost and side effects of maneuvering

Every avoidance maneuver burns propellant — and propellant is mission lifetime. It can also disrupt the mission (imaging windows, comms coverage) and, critically, create new conjunctions downstream that have to be screened all over again.

The hard part: coordination between operators

If only one object can maneuver, the decision is yours alone. But when both objects are active, maneuvering satellites, you have a coordination problem. If both operators act independently on the same alert, they can each dodge — straight into each other. Resolving this today means analysts contacting each other directly, often by email, under time pressure. It works at low volumes and fails badly as conjunction counts climb into the thousands per year.

Why this is getting harder — fast

Three trends are compounding:

• More objects — over 12,000 active satellites today, heading toward 100,000+ in the early 2030s.
• More conjunctions — risk scales with the square of object count, not linearly.
• More maneuverable spacecraft — meaning more events that require two-sided coordination, not a one-sided dodge.

The result is that conjunction assessment is shifting from an occasional analyst task to a near-continuous, high-volume operation that human-paced, email-based workflows can't keep up with.

Toward automated conjunction assessment

The response is automation: systems that ingest CDMs continuously, model uncertainty consistently, flag the events that genuinely warrant action, and coordinate maneuvers between operators automatically and fairly. That removes human delay from the critical path and prevents the uncoordinated-dodge failure mode. This is precisely what Space Guardian is building — autonomous risk prediction and fair maneuver negotiation for a crowded orbit.

Key takeaways

• Conjunction assessment is risk evaluation under uncertainty, not just measuring a miss distance.
• The CDM's probability of collision, time of closest approach, and covariance drive the decision — read them together, and watch the trend across updates.
• Maneuvers cost fuel and can spawn new conjunctions, so thresholds and timing matter.
• Two-sided coordination is the emerging bottleneck, and automation is the way through it.

Curious how automated, fair maneuver coordination would work for your fleet? [Talk to us](/contact).