CDM (Conjunction Data Message)

The Conjunction Data Message (CDM) is a standardized format for communicating close-approach assessment data between spacecraft operators and tracking organizations. Use this page to prepare a complete .cdm file for the Import dialog on the conjunctions page and to check the required metadata, state vectors, and covariance terms before uploading.

For the complete documentation index, see llms.txt.

Key Components

Component	Description
Header	Message metadata including format version, creation date, and originator information.
Relative metadata	Conjunction information such as Time of Closest Approach (TCA), miss distance, relative speed, and collision probability.
Object metadata	Identification, covariance method, maneuverability, and reference-frame information for both objects.
Object data	A state vector and covariance matrix for each object.

Critical Fields

Field	Description	Unit
TCA	The UTC timestamp when the two objects are closest.	UTC
MISS_DISTANCE	Overall separation distance between objects at TCA.	m
COLLISION_PROBABILITY	Statistical probability of collision.	Dimensionless, from `0.0` to `1.0`
RELATIVE_SPEED	Magnitude of relative velocity.	m/s
Covariance terms	The lower-triangular uncertainty matrix for each object.	See Covariance Matrix

Object Data Requirements

Each object block in an importable CDM must contain the following:

Requirement	What to Include
Object identity	`OBJECT_DESIGNATOR`, `OBJECT_NAME`, and `INTERNATIONAL_DESIGNATOR` when available.
State vector	`X`, `Y`, `Z`, `X_DOT`, `Y_DOT`, and `Z_DOT`, with units in `km` and `km/s`.
Reference frame	`REF_FRAME`, such as `EME2000`.
Covariance method	`COVARIANCE_METHOD`, such as `CALCULATED`, when covariance data is provided. Include it for both objects.
Covariance matrix	All 21 lower-triangular covariance terms for the object. Do not omit the position-velocity or velocity-velocity terms.

Covariance Matrix

The covariance matrix has 21 independent lower-triangular terms for each object. Include every term in the following groups:

Matrix Block	Required Terms	Unit
Position-position	`CR_R`, `CT_R`, `CT_T`, `CN_R`, `CN_T`, `CN_N`	`m**2`
Position-velocity	`CRDOT_R`, `CRDOT_T`, `CRDOT_N`, `CTDOT_R`, `CTDOT_T`, `CTDOT_N`, `CNDOT_R`, `CNDOT_T`, `CNDOT_N`	`m**2/s`
Velocity-velocity	`CRDOT_RDOT`, `CTDOT_RDOT`, `CTDOT_TDOT`, `CNDOT_RDOT`, `CNDOT_TDOT`, `CNDOT_NDOT`	`m2/s2`

Common Use Cases

Conjunction assessment: Share close-approach predictions for collision-risk analysis.
Collision avoidance: Provide the state and uncertainty data used to evaluate a conjunction.
STM exchange: Transfer a conjunction prediction between a tracking provider and a spacecraft operator.

See the complete CCSDS 508.0-B-1 CDM standard for the authoritative format definition.

Worked Example

The following KVN example is complete and can be used as a starting point. It includes COVARIANCE_METHOD and all 21 covariance terms for both objects.

CCSDS_CDM_VERS = 1.0
CREATION_DATE = 2024-06-15T12:30:00.000
ORIGINATOR = SPACE-TRACK
MESSAGE_FOR = ISS (ZARYA)
MESSAGE_ID = SPACE-TRACK_CDM_001

COMMENT This is a complete example. All timestamps are UTC.

TCA = 2024-06-20T14:30:45.500
MISS_DISTANCE = 847.5 [m]
RELATIVE_SPEED = 14500.0 [m/s]
RELATIVE_POSITION_R = 125.3 [m]
RELATIVE_POSITION_T = -623.7 [m]
RELATIVE_POSITION_N = 498.2 [m]
RELATIVE_VELOCITY_R = -1.25 [m/s]
RELATIVE_VELOCITY_T = 14499.5 [m/s]
RELATIVE_VELOCITY_N = 0.85 [m/s]
START_SCREEN_PERIOD = 2024-06-20T14:00:00.000
STOP_SCREEN_PERIOD = 2024-06-20T15:00:00.000
SCREEN_VOLUME_FRAME = RTN
SCREEN_VOLUME_SHAPE = ELLIPSOID
SCREEN_VOLUME_X = 50000.0 [m]
SCREEN_VOLUME_Y = 50000.0 [m]
SCREEN_VOLUME_Z = 50000.0 [m]
SCREEN_ENTRY_TIME = 2024-06-20T14:29:30.000
SCREEN_EXIT_TIME = 2024-06-20T14:31:30.000
COLLISION_PROBABILITY = 5.678E-05
COLLISION_PROBABILITY_METHOD = FOSTER-1992

OBJECT = OBJECT1
OBJECT_DESIGNATOR = 25544
CATALOG_NAME = SATCAT
OBJECT_NAME = ISS (ZARYA)
INTERNATIONAL_DESIGNATOR = 1998-067A
OBJECT_TYPE = PAYLOAD
OPERATOR_CONTACT_POSITION = Flight Director
OPERATOR_ORGANIZATION = NASA
OPERATOR_PHONE = +1-281-483-0000
OPERATOR_EMAIL = flightdirector@nasa.gov
EPHEMERIS_NAME = JSC EPHEMERIS
COVARIANCE_METHOD = CALCULATED
MANEUVERABLE = YES
ORBIT_CENTER = EARTH
REF_FRAME = EME2000
GRAVITY_MODEL = EGM-96: 36D 36O
ATMOSPHERIC_MODEL = JACCHIA 70 DCA
N_BODY_PERTURBATIONS = MOON,SUN
SOLAR_RAD_PRESSURE = YES
EARTH_TIDES = YES
INTRACK_THRUST = NO

COMMENT Object 1 State Vector
X = 6778.137 [km]
Y = 0.0 [km]
Z = 0.0 [km]
X_DOT = 0.0 [km/s]
Y_DOT = 7.668 [km/s]
Z_DOT = 0.0 [km/s]

COMMENT Object 1 Covariance Matrix RTN
CR_R = 4.142E+01 [m**2]
CT_R = 5.461E+01 [m**2]
CT_T = 2.345E+02 [m**2]
CN_R = -3.456E+00 [m**2]
CN_T = 1.234E+01 [m**2]
CN_N = 9.876E+01 [m**2]
CRDOT_R = -3.878E-02 [m**2/s]
CRDOT_T = 5.213E-02 [m**2/s]
CRDOT_N = -1.234E-03 [m**2/s]
CRDOT_RDOT = 6.789E-05 [m**2/s**2]
CTDOT_R = 5.678E-02 [m**2/s]
CTDOT_T = -4.321E-02 [m**2/s]
CTDOT_N = 2.345E-03 [m**2/s]
CTDOT_RDOT = -1.234E-05 [m**2/s**2]
CTDOT_TDOT = 8.765E-05 [m**2/s**2]
CNDOT_R = 1.111E-03 [m**2/s]
CNDOT_T = -2.222E-03 [m**2/s]
CNDOT_N = 3.333E-03 [m**2/s]
CNDOT_RDOT = 4.444E-06 [m**2/s**2]
CNDOT_TDOT = -5.555E-06 [m**2/s**2]
CNDOT_NDOT = 6.666E-06 [m**2/s**2]

OBJECT = OBJECT2
OBJECT_DESIGNATOR = 43567
CATALOG_NAME = SATCAT
OBJECT_NAME = COSMOS 2251 DEB
INTERNATIONAL_DESIGNATOR = 2009-043FG
OBJECT_TYPE = DEBRIS
EPHEMERIS_NAME = NORAD TLE
COVARIANCE_METHOD = CALCULATED
MANEUVERABLE = N/A
ORBIT_CENTER = EARTH
REF_FRAME = EME2000

COMMENT Object 2 State Vector
X = 6778.260 [km]
Y = 0.125 [km]
Z = -0.498 [km]
X_DOT = 0.001 [km/s]
Y_DOT = 7.669 [km/s]
Z_DOT = -0.001 [km/s]

COMMENT Object 2 Covariance Matrix RTN
CR_R = 8.234E+02 [m**2]
CT_R = 1.567E+02 [m**2]
CT_T = 5.678E+03 [m**2]
CN_R = -2.345E+01 [m**2]
CN_T = 3.456E+02 [m**2]
CN_N = 4.567E+02 [m**2]
CRDOT_R = -7.890E-01 [m**2/s]
CRDOT_T = 1.234E+00 [m**2/s]
CRDOT_N = -5.678E-02 [m**2/s]
CRDOT_RDOT = 9.012E-04 [m**2/s**2]
CTDOT_R = 1.111E+00 [m**2/s]
CTDOT_T = -2.222E+00 [m**2/s]
CTDOT_N = 3.333E-01 [m**2/s]
CTDOT_RDOT = -4.444E-04 [m**2/s**2]
CTDOT_TDOT = 5.555E-03 [m**2/s**2]
CNDOT_R = 6.666E-02 [m**2/s]
CNDOT_T = -7.777E-02 [m**2/s]
CNDOT_N = 8.888E-02 [m**2/s]
CNDOT_RDOT = 9.999E-05 [m**2/s**2]
CNDOT_TDOT = -1.111E-04 [m**2/s**2]
CNDOT_NDOT = 2.222E-04 [m**2/s**2]

Save the example with the .cdm extension before uploading it. Replace the primary object’s identifiers with a spacecraft registered in your VALAR fleet; otherwise the file can be structurally valid but cannot be linked to a spacecraft during import.

Importing a CDM in VALAR

Open Conjunctions at /conjunctions/current.
Click Import to open the Import Alerts dialog.
Drag and drop one or more .cdm files into the upload area, or click Drag and drop files here or click to browse.
Confirm that the primary object in each file matches a registered spacecraft by NORAD ID or COSPAR ID.
Click Import.

If the file is structurally incomplete, VALAR rejects it without importing a partial conjunction. Regenerate the CDM with complete metadata, state vectors, and covariance terms instead of filling missing uncertainty values with zeros.

Differences Between CDM and Other Formats

Attribute	CDM	OPM	OEM
Temporal Scope	One conjunction event at a TCA.	One spacecraft state at one epoch.	A time-ordered trajectory.
Primary Content	Two-object close-approach data, state vectors, and covariance.	One spacecraft state vector with optional elements and maneuvers.	Multiple spacecraft state vectors with optional covariance.
Primary Use	Conjunction assessment and collision-risk analysis.	State-vector exchange and import.	Ephemeris exchange and propagation.

Conjunction classification: Review conjunction criticality and risk categories.
Conjunction computation: Compute conjunction events from spacecraft states.
File format overview: Compare the orbital and mission file formats supported by VALAR.

Core Concepts

File Formats

Key Components

Critical Fields

Object Data Requirements

Covariance Matrix

Common Use Cases

Worked Example

Importing a CDM in VALAR

Differences Between CDM and Other Formats

​Key Components

​Critical Fields

​Object Data Requirements

​Covariance Matrix

​Common Use Cases

​Worked Example

​Importing a CDM in VALAR

​Differences Between CDM and Other Formats

​Related Pages

Key Components

Critical Fields

Object Data Requirements

Covariance Matrix

Common Use Cases

Worked Example

Importing a CDM in VALAR

Differences Between CDM and Other Formats

Related Pages