Conjunction Assessment

Conjunction assessment is a critical space safety process that identifies and evaluates close approaches between space objects, enabling operators to take collision avoidance action when necessary.

Process Steps

1. Screening: Identify potential close approaches from catalog data

1. Refinement: Improve accuracy with additional observations

1. Risk Assessment: Calculate collision probability

1. Decision: Determine if avoidance maneuver is needed

1. Coordination: Communicate with other operators if applicable

1. Execution: Perform maneuver if required

1. Verification: Confirm post-maneuver safety

Key Metrics

• Time of Closest Approach (TCA)

• Miss distance

• Collision probability (Pc)

• Mahalanobis distance

Thresholds Typical action thresholds:

• Pc > 10⁻⁴: Maneuver recommended

• Pc > 10⁻³: Maneuver strongly advised

• Miss distance < 1 km (LEO): Close monitoring

Regulatory Requirements Under the EU Space Act proposal (COM(2025) 335, not in force), Union spacecraft operators would have to:

• Subscribe to the collision avoidance services of the EU SST provider (Art. 64(1))

• Inform that provider without delay of planned changes, of the decision to start the disposal and end-of-life phase (three months in advance) and of unplanned changes affecting compliance (Art. 64(3))

• Report all actions taken after a high interest event alert (Art. 64(5))

• Have manoeuvrability for orbits with an apogee above 400 km (Art. 66)