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Conjunction Risk Assessment

Conjunction Risk Assessment

Frequently Asked Questions

CARA Process Overview

Basic Definitions

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CARA Process Overview

The CARA operations process is a three-step process involving the CARA Orbital Safety Analysts (OSAs) resident at the 18th SDS (Space Defense Squadron) operations facility at Vandenberg Space Force Base (VSFB), the NASA CARA team, and the mission Owner/Operator (O/O).

The first step, Conjunction Assessment (CA), is the prediction of close approaches by “screening” the trajectory of the protected asset against the High Accuracy Catalog (HAC). This step is performed by the CARA OSAs using two asset trajectories – one provided by the owner/operator (O/O) that contains any planned maneuvers during the prediction span, and the other based on non-cooperative tracking data from the DoD Space Surveillance Network (SSN) that does not have any information about upcoming maneuvers. Results of both screening runs are transferred to CARA via SFTP 3x/day for LEO spacecraft and 2x/day for all others.

Step two is risk assessment. CARA has an automated tool, the Conjunction Assessment System (CAS), which processes the data and sends updated trending information to the mission customer. The CARA team then manually analyzes any conjunctions that they consider to be high risk to determine appropriate actions to be taken (i.e. Conjunction Assessment Risk Analysis).

Step three is Collision Avoidance, in which CARA works with the mission to assist with planning and execution of any risk mitigation strategies. A summary of the process is shown in Figure 3.

conjunction services flow chart

Basic Definitions:

  • A conjunction is defined here to mean a local minimum in the difference between the position components of two trajectories – the closest point of approach
  • Conjunction Assessment (CA) is the process of predicting the conjunction event by screening the ephemeris of the protected asset against the space object catalog
  • Conjunction Assessment Risk Analysis (CARA) is the process of analyzing the conjunction event to determine the associated threat to the asset
  • Collision Avoidance is the process by which the risk associated with a conjunction event is mitigated — by a maneuver or other action.