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The Conjunction Data Message (CDM) is a standardized format for communicating close approach (conjunction) assessment data between spacecraft operators and tracking organizations. Each CDM represents a single conjunction event between two space objects and includes critical information for collision risk assessment.

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Key Components

A CDM contains several distinct sections:
  • Header: General message metadata including format version, creation date, and originator information
  • Relative Metadata/Data: Conjunction-specific information such as Time of Closest Approach (TCA), miss distance, relative speed, and collision probability
  • Object Metadata: Identification and reference frame information for both objects involved in the conjunction
  • Object Data: State vectors (position and velocity) and covariance matrices for each object, providing position uncertainty information

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Critical Fields

  • TCA (Time of Closest Approach): The UTC timestamp when the two objects are closest
  • MISS_DISTANCE: Overall separation distance between objects at TCA (meters)
  • COLLISION_PROBABILITY: Statistical probability of collision (0.0 to 1.0)
  • RELATIVE_SPEED: Magnitude of relative velocity between objects (m/s)
  • Covariance Matrices: Uncertainty ellipsoids for each object’s position
Complete definition of the CDM standard on CCSDS 508.0-B-1 guidelines.
Here is a sample CDM file in KVN format: 
CCSDS_CDM_VERS             = 1.0
CREATION_DATE              = 2024-07-04T10:00:00.000
ORIGINATOR                 = VALAR
MESSAGE_ID                 = CDM-2024-001

TCA                        = 2024-07-04T12:00:00.000
MISS_DISTANCE              = 437 [m]
RELATIVE_SPEED             = 14850.5 [m/s]
RELATIVE_POSITION_R        = 350.0 [m]
RELATIVE_POSITION_T        = -120.5 [m]
RELATIVE_POSITION_N        = 245.8 [m]
COLLISION_PROBABILITY      = 0.000003656957
COLLISION_PROBABILITY_METHOD = FOSTER-1992

OBJECT                     = OBJECT1
OBJECT_DESIGNATOR          = 2023-001A
CATALOG_NAME               = SATCAT
OBJECT_NAME                = SPACECRAFT-1
INTERNATIONAL_DESIGNATOR   = 2023-001A
EPHEMERIS_NAME             = EPHEMERIS-001
REF_FRAME                  = EME2000
GRAVITY_MODEL              = EGM-96: 36D 36O
TIME_LASTOB_START          = 2024-07-03T18:00:00.000
TIME_LASTOB_END            = 2024-07-04T06:00:00.000

X                          = 6655.994 [km]
Y                          = -40218.575 [km]
Z                          = -82.918 [km]
X_DOT                      = 3.115482 [km/s]
Y_DOT                      = 0.470426 [km/s]
Z_DOT                      = -0.001015 [km/s]

CR_R                       = 4.142e+01 [m**2]
CT_R                       = -8.579e+00 [m**2]
CT_T                       = 5.189e+01 [m**2]
CN_R                       = -4.788e+01 [m**2]
CN_T                       = -4.472e+01 [m**2]
CN_N                       = 5.960e+01 [m**2]

OBJECT                     = OBJECT2
OBJECT_DESIGNATOR          = 1997-051C
CATALOG_NAME               = SATCAT
OBJECT_NAME                = DEBRIS-FRAGMENT
INTERNATIONAL_DESIGNATOR   = 1997-051C
EPHEMERIS_NAME             = EPHEMERIS-002
REF_FRAME                  = EME2000

X                          = 6656.344 [km]
Y                          = -40218.695 [km]
Z                          = -82.672 [km]
X_DOT                      = -0.885518 [km/s]
Y_DOT                      = -0.530574 [km/s]
Z_DOT                      = 0.000985 [km/s]

CR_R                       = 1.337e+03 [m**2]
CT_R                       = 2.520e+03 [m**2]
CT_T                       = 5.886e+03 [m**2]
CN_R                       = -3.476e+02 [m**2]
CN_T                       = -7.840e+02 [m**2]
CN_N                       = 7.533e+01 [m**2]