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For the complete documentation index, see llms.txt.
The Orbit Parameter Message (OPM) is a standardized ASCII text format for exchanging spacecraft orbital state information at a single epoch. Unlike OEM which contains time-series ephemeris data, OPM represents a snapshot of spacecraft state and can include optional physical parameters and a single impulsive maneuver definition.

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Key Components

An OPM file contains several distinct sections:
  • Header: File-level metadata including format version, creation date, and originator
  • Metadata: Orbital context such as object identification, reference frame, and time system
  • State Vector: Spacecraft position and velocity at a specific epoch (Cartesian coordinates)
  • Keplerian Elements (Optional): Alternative orbital element representation (semi-major axis, eccentricity, inclination, etc.)
  • Spacecraft Parameters (Optional): Physical properties for orbit propagation (mass, drag coefficient, solar radiation pressure)
  • Maneuver Parameters (Optional): Single impulsive maneuver definition with delta-V components

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State Representation Options

OPM supports two ways to represent orbital state:

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Cartesian State Vector

Position (X, Y, Z) and velocity (X_DOT, Y_DOT, Z_DOT) in a specified reference frame:
  • X, Y, Z: Position components in kilometers
  • X_DOT, Y_DOT, Z_DOT: Velocity components in km/s

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Keplerian Elements (Optional Alternative)

Classical orbital elements describing the same state:
  • SEMI_MAJOR_AXIS: Size of the orbit (km)
  • ECCENTRICITY: Shape of the orbit (0 = circular, less than 1 = elliptical)
  • INCLINATION: Angle between orbital plane and reference plane (degrees)
  • RA_OF_ASC_NODE: Right ascension of ascending node (degrees)
  • ARG_OF_PERICENTER: Argument of periapsis (degrees)
  • TRUE_ANOMALY: Position along orbit (degrees)

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Spacecraft Physical Parameters

OPM can include physical properties required for accurate orbit propagation:
  • MASS: Spacecraft mass (kg)
  • SOLAR_RAD_AREA: Effective area for solar radiation pressure (m²)
  • SOLAR_RAD_COEFF: Solar radiation pressure coefficient
  • DRAG_AREA: Effective area for atmospheric drag (m²)
  • DRAG_COEFF: Atmospheric drag coefficient

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Common Use Cases

  • Orbit Determination Results: Sharing fitted state vectors after measurement processing
  • State Vector Import: Loading initial conditions into mission planning systems
  • Data Exchange: Transferring orbital state between organizations
  • Mission Analysis: Providing reference states for trajectory studies
Complete definition of the OPM standard on CCSDS 502.0-B-3 guidelines.
Here is a sample OPM file in KVN format: 
CCSDS_OPM_VERS       = 3.0
CREATION_DATE        = 2024-06-03T05:33:00.000
ORIGINATOR           = VALAR

COMMENT Orbit determination solution from tracking pass
COMMENT State vector after maneuver execution

OBJECT_NAME          = SPACECRAFT-ALPHA
OBJECT_ID            = 2023-001A
CENTER_NAME          = EARTH
REF_FRAME            = EME2000
TIME_SYSTEM          = UTC

EPOCH                = 2024-06-03T00:00:00.000
X                    = 6655.9942 [km]
Y                    = -40218.5751 [km]
Z                    = -82.9177 [km]
X_DOT                = 3.11548208 [km/s]
Y_DOT                = 0.47042605 [km/s]
Z_DOT                = -0.00101495 [km/s]

COMMENT Spacecraft physical parameters for propagation

MASS                 = 1913.000 [kg]
SOLAR_RAD_AREA       = 10.000 [m**2]
SOLAR_RAD_COEFF      = 1.300
DRAG_AREA            = 10.000 [m**2]
DRAG_COEFF           = 2.300

COMMENT Planned orbit-raising maneuver

MAN_EPOCH_IGNITION   = 2024-06-03T09:00:34.1
MAN_DURATION         = 132.60 [s]
MAN_DELTA_MASS       = -18.418 [kg]
MAN_REF_FRAME        = RTN
MAN_DV_1             = -0.02325700 [km/s]
MAN_DV_2             = 0.01683160 [km/s]
MAN_DV_3             = -0.00893444 [km/s]

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OPM with Keplerian Elements Example

CCSDS_OPM_VERS       = 3.0
CREATION_DATE        = 2024-06-03T05:33:00.000
ORIGINATOR           = VALAR

OBJECT_NAME          = SPACECRAFT-BETA
OBJECT_ID            = 2023-002B
CENTER_NAME          = EARTH
REF_FRAME            = EME2000
TIME_SYSTEM          = UTC

EPOCH                = 2024-06-03T12:00:00.000

COMMENT Keplerian elements representation

SEMI_MAJOR_AXIS      = 42164.140 [km]
ECCENTRICITY         = 0.0001234
INCLINATION          = 0.05 [deg]
RA_OF_ASC_NODE       = 75.123 [deg]
ARG_OF_PERICENTER    = 180.456 [deg]
TRUE_ANOMALY         = 90.789 [deg]

MASS                 = 2500.000 [kg]
SOLAR_RAD_AREA       = 15.000 [m**2]
SOLAR_RAD_COEFF      = 1.200
DRAG_AREA            = 12.000 [m**2]
DRAG_COEFF           = 2.200

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Differences Between OPM and Other Formats

FeatureOPMOEMOCM
Temporal ScopeSingle epochTime seriesSingle or multiple epochs
ManeuversOne impulsive maneuverNot supportedMultiple maneuvers
Keplerian ElementsOptionalNot supportedOptional
CovariancesOptionalOptional per epochOptional
Primary Use CaseState snapshots, OD outputEphemeris sharingComprehensive mission plans

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SpaceX OPM Format

SpaceX provides state vectors to customers via a proprietary OPM variant derived from the CCSDS standard. This format is generated from Falcon second stage flight telemetry and has several key differences from standard CCSDS OPM.
The SpaceX OPM represents the state of the second stage, not the deployed spacecraft. Any position, velocity, attitude, or attitude-rate differences between the second stage and your spacecraft at separation must be accounted for by the recipient.

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SpaceX OPM Fields

FieldDescriptionUnits
UTC time at liftoffLaunch time referenceDOY:HH:MM:SS.SS
UTC time of current stateEpoch of the state vectorDOY:HH:MM:SS.SS
Mission elapsed timeTime since liftoffseconds
ECEF Position (X,Y,Z)Position in WGS84 ECEF framemeters
ECEF Velocity (X,Y,Z)Earth-relative velocity in ECEFm/s
LVLH to BODY quaternionAttitude quaternion (scalar-first: S,X,Y,Z)dimensionless
Inertial body rates (X,Y,Z)Angular velocitydeg/s
Apogee AltitudeMaximum altitude (spherical Earth)km
Perigee AltitudeMinimum altitude (spherical Earth)km
InclinationOrbital inclinationdegrees
Argument of PerigeeOrientation of orbit ellipsedegrees
Longitude of Asc. NodeAscending node referenced to Greenwichdegrees
True AnomalyPosition along orbitdegrees

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Key Differences from CCSDS OPM

AspectCCSDS OPMSpaceX OPM
Reference FrameInertial (EME2000, GCRF)WGS84 ECEF, inertially frozen at state epoch
Position Unitskilometersmeters
Velocity Unitskm/sm/s
Velocity ReferenceInertialEarth-relative
Time FormatISO 8601Day-of-Year (DOY:HH:MM:SS.SS)
Ascending NodeRight Ascension (vernal equinox)Longitude (Greenwich Meridian)
Altitude ReferenceTypically WGS84 ellipsoidSpherical Earth (6378.137 km radius)
Attitude DataNot includedLVLH-to-body quaternion + body rates

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Sample SpaceX OPM

SpaceX OPM output (generated 2024-06-15-Sat-14-30-00):
All orbital elements are defined as osculating at the instant of the printed state.
Orbital elements are computed in an inertial frame realized by inertially freezing
the WGS84 ECEF frame at time of current state.

UTC time at liftoff:        166:14:00:00.00
UTC time of current state:  166:14:45:30.25
Mission elapsed time (s):   +2730.25

ECEF (X,Y,Z) Position (m):           +4523156.789, -3298765.432, +4012345.678
ECEF (X,Y,Z) Velocity* (m/s):        +5234.567, +4123.456, -3456.789

LVLH to BODY quaternion (S,X,Y,Z):   +0.7071068, +0.0000000, +0.7071068, +0.0000000
Inertial body rates (X,Y,Z) (deg/s): +0.0012345, -0.0023456, +0.0034567

Apogee Altitude** (km):              +00850.123
Perigee Altitude** (km):             +00320.456
Inclination (deg):                   +53.215
Argument of Perigee (deg):           +090.123
Longitude of the Asc. Node*** (deg): +125.678
True Anomaly (deg):                  +45.890

Notes:
* ECEF velocity is Earth-relative
** Apogee/Perigee altitude assumes a spherical Earth, 6378.137 km radius
*** LAN is defined as the angle between Greenwich Meridian and the ascending node

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Importing SpaceX OPM in VALAR

When importing SpaceX OPM files:
  1. Select SpaceX OPM as the format in the import dialog
  2. VALAR automatically converts the ECEF state to an inertial frame
  3. The Longitude of Ascending Node is converted to Right Ascension
  4. Position and velocity units are converted from meters to kilometers
SpaceX OPM format is documented in the Falcon User’s Guide. VALAR’s SpaceX OPM parser handles all necessary coordinate transformations automatically.