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Conjunction Events

A conjunction event is a close approach between two objects at roughly the same time.

When the conjunction screening system generates a CDM whose time of closest approach (TCA) is within 20 minutes of an existing conjunction event, a new one is created.

As operators continue to submit trajectories associated with these objects over time, more CDMs may be associated with the conjunction event.

Conjunction Event Properties

A conjunction event is identified by a UUID4 in the screening system.

A conjunction event has the following additional properties:

  • References to the objects and operators associated with the conjunction.
  • The creation time of the event
  • A reference to the "active CDM", i.e., the most recent CDM generated for the event.
  • A series of parameters passed through from the active CDM:
    • Time of Closest Approach (TCA)
    • Probability of Collision (Pc)
    • The trajectory IDs associated
  • The "claim status" for each operator (see below).

The system may assign a NULL value to the "active CDM" for a conjunction event if the risk for the event is fully mitigated; that is, an operator submits a trajectory for one of the objects that reduces risk such that no CDM is generated.

Maneuver Responsibility Coordination

Conjunction events are the basis for maneuver coordination between operators. This has a few benefits:

  • Operators don't have to coordinate maneuver responsibility for multiple CDMs that physically represent the same close approach.
  • The system is unambiguous about when risk has been fully mitigated for a conjunction event; the system explicitly assigns a NULL value to distinguish between cases where the most recent trajectory hasn't been screened, and cases where it has been screened and is completely outside the screening box.

Claim statuses

Conjunction events contain a "claim status" for each operator that is party to a conjunction event, which is one of three options:

Claim StatusDescription
claimedThe operator has claimed responsibility for resolving risk for this conjunction, and soon plans to submit a modified trajectory.
unclaimedThis is the default value that all conjunctions start at, meaning the operator has not assumed (or rejected) responsibility yet.
rejectedThe operator has explicitly rejected responsibility for this conjunction. This signals to the other party they must be the one to act, if necessary (e.g., if a satellite is non-maneuverable, or the decision window has passed for a satellite to perform a maneuver)


Claiming maneuver responsibility is intended to serve as an implicit "lock" on submission of new trajectories, to eliminate ambiguity about who is going to maneuver. Therefore, it is good etiquette to:

  • Submit a trajectory that mitigates the risk of the conjunction event shortly after claiming it.
  • Once you have mitigated the risk of the conjunction event, returning the claim status to unclaimed

To make this easier, an optional field auto_relinquish_pc_threshold is provided when submitting trajectories. If the submitted trajectory reduces the probability of collision for any associated events below this threshold, the system will automatically remove that operator's maneuver claim for that event.

By default, only one operator can claim responsibility for an event, but it is possible for both operators to claim responsibility by setting the "force" flag in requests to the POST /api/v1/event/{id}/claim to "true". Operators may use the force flag in situations where the opposing operator has claimed responsibility, but failed to submit an updated trajectory.