Satellite operators prevent close approaches from becoming collisions through a data-and-decision chain: orbit information is exchanged, assessment services screen predicted trajectories and send conjunction information in a Conjunction Data Message (CDM), and the operator evaluates the changing risk before deciding whether to maneuver. A CDM reports an assessment; it does not command or execute a maneuver.
How orbit data becomes a conjunction warning
- Orbit information is shared. Operators and other authorized parties provide orbit data to an assessment service or exchange it with another organization. The data may describe a predicted trajectory or a more detailed orbit history.
- A service screens the trajectories. The assessment provider compares available orbit information and predicts whether two objects will pass close to one another. Some services can screen an operator’s predictive ephemeris and return results in CDM format.
- The service issues a CDM. If it identifies a conjunction, it sends a message containing information about the predicted event and closest approach. The CDM gives the operator information for assessing collision risk and, if needed, designing an avoidance maneuver.
- The mission team assesses and coordinates. Flight-dynamics and flight-control teams, mission managers, and other responsible personnel review the event, seek updated assessments as needed, and decide on an operational response.
This separates three things that are easy to conflate: the orbit data being exchanged, the provider’s conjunction assessment, and the operator’s decision about what to do. CCSDS publishes the CDM as a standardized format for exchanging conjunction information among assessment originators, satellite owner/operators, and other authorized parties. Its listing identifies Issue 1 as June 2013, with technical corrigenda through October 2021.
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Which messages carry orbit and conjunction information?
Orbit Data Message (ODM) is a family of formats for sharing orbit information. NOAA’s Office of Space Commerce standards recommendations identify four members; the CDM is a separate message for conjunction-assessment information.
| Message | What it carries | How it fits the exchange |
|---|---|---|
| Orbit Parameter Message (OPM) | Orbit parameters | One of the ODM formats identified in the Office of Space Commerce’s recommendations on standards. |
| Orbit Mean-Elements Message (OMM) | Mean orbital elements | An ODM format for conveying orbit information. |
| Orbit Ephemeris Message (OEM) | Orbit ephemeris data | An ODM format for conveying orbit information. |
| Orbit Comprehensive Message (OCM) | Comprehensive orbit-related information | An ODM format for conveying orbit information. |
| Conjunction Data Message (CDM) | Conjunction-assessment information associated with a predicted close approach | Communicates assessment results so an operator can assess risk and consider a response; it is not a maneuver command. |
The Office of Space Commerce says ODM exchanges support conjunction studies as well as tracking, navigation, orbit comparison, and other operational needs. Format choice and the exact information exchanged depend on the service and operational context. The 2025 TraCSS CDM specification described KVN, XML, and JSON encodings, with the same information represented across them. The Office of Space Commerce announced updated TraCSS specifications on January 22, 2026, including CDM, OMM, OCM, and catalog-format specifications; implementation details should be checked against the applicable current specification rather than assumed from the 2025 version.
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Who exchanges data with whom?
There is no single source of orbit data or single assessment provider used by every operator. The providers and data paths described by U.S. and European services illustrate different arrangements:
- U.S. Space-Track services: Space-Track documentation describes 18th Space Defense Squadron (18 SDS) services that screen operator-provided predictive ephemeris and return results in CDM format. Its operator resources also include close-approach notifications, example message formats, and maneuver-notification information.
- ESA’s service: The European Space Agency says it combines CDMs received under a data-sharing agreement with U.S. Strategic Command with ESA’s own orbit data. Its conjunction assessment service supports ESA missions and missions flown by other agencies; a web interface lets flight-control teams, flight-dynamics teams, and mission managers review event details and assessment history.
- TraCSS: The U.S. Department of Commerce’s Traffic Coordination System for Space began accepting satellite owner/operator registrations directly through its webpage in early 2026. NOAA’s Office of Space Commerce reported in August 2026 that 82 pilot user organizations representing more than 11,370 satellites, along with 10 national government accounts, had onboarded. Those are dated pilot-program figures, not a permanent system total or evidence that all operators use TraCSS.
Commercial conjunction-assessment screening is another service category. The Office of Space Commerce has described a commercial screening-services pilot and a commercial SSA provider participating in a COLA Gap Pathfinder initiative. Provider access, eligibility, data policies, and ongoing service availability should be confirmed with the provider; the existence of a pilot does not establish universal access.
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What does an operator assess in a CDM?
A predicted miss distance alone does not determine whether a close approach is dangerous. ESA identifies object sizes, predicted miss distance, flyby geometry, and the orbit uncertainties of both objects as factors in collision risk. Operators also need to consider when the encounter will occur and how the assessment changes as new observations and orbit information become available.
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- Event timing and geometry: establish when the predicted closest approach occurs and the nature of the flyby.
- Miss distance and object size: consider the predicted separation in relation to the objects involved, rather than treating distance as a risk score by itself.
- Uncertainty: account for uncertainty in both predicted orbits; a prediction is not an exact future position.
- Assessment history: compare successive assessments. ESA says its service updates predictions several times a day and retains event history, illustrating why risk may change as data is refreshed.
- Potential response: where relevant, provide updated ephemeris or proposed maneuver information to the assessment service so the planned response can be evaluated.
Data-sharing workflows, access rules, update cadence, and decision thresholds vary by provider and mission. There is no single global probability threshold or automatic rule in the cited service descriptions that requires every operator to maneuver.
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Who decides whether to maneuver?
The assessment service supplies information; the mission operator makes the operational decision under its mission procedures. Space-Track’s documentation says that collision avoidance is the satellite owner/operator’s responsibility, while 18 SDS supports those efforts by screening predictive ephemeris and returning results in CDM format. That is Space-Track’s description of its service and should not be read as a universal legal rule for every jurisdiction.
In practice, teams may coordinate internally across flight dynamics, flight control, and mission management, and exchange updated orbit or maneuver information with the relevant assessment service. A planned maneuver can alter the predicted encounter, so the operator may need follow-up screening to understand the resulting trajectory and any new close approaches. The exact coordination sequence is mission- and provider-specific.
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Why one service’s alert rate or threshold does not apply to every satellite
ESA’s “Automating collision avoidance” page offers a historical, fleet-specific illustration: it described hundreds of alerts per week for a typical satellite in low Earth orbit and about two alerts per week per satellite requiring detailed follow-up for ESA’s current fleet in those low-altitude orbits. The same page described ESA’s process as preparing a maneuver when collision probability was typically greater than 1 in 10,000. These figures describe ESA’s context at the time of that page, not a current universal alert rate or a threshold for other operators.
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1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsThe services described here cover U.S. government, European, and commercial contexts, but they do not establish one worldwide provider, message version, data-sharing agreement, eligibility policy, risk threshold, or maneuver protocol. Operators must follow the applicable service’s current specifications and policies together with their mission rules.
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