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The Orbit Mean-elements Message (OMM) is a standardized ASCII text format for exchanging spacecraft mean Keplerian orbital elements at a single epoch. Unlike OPM which uses osculating (instantaneous) elements, OMM provides mean elements that have been averaged over short-period perturbations, making them suitable for catalog distribution and TLE-equivalent data exchange.

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Key Components

An OMM 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, center name, and time system
  • Mean Keplerian Elements: Six classical orbital elements averaged over short-period perturbations
  • TLE-Related Parameters (Optional): SGP4/SDP4 propagation parameters for compatibility with TLE-based systems
  • Covariance (Optional): Uncertainty information for the mean orbital state

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Mean Keplerian Elements

OMM uses mean elements — orbital parameters that have been averaged to remove short-period oscillations caused by Earth’s oblateness and other perturbations:
  • SEMI_MAJOR_AXIS: Mean semi-major axis (km)
  • ECCENTRICITY: Mean eccentricity (dimensionless)
  • INCLINATION: Mean inclination (degrees)
  • RA_OF_ASC_NODE: Mean right ascension of the ascending node (degrees)
  • ARG_OF_PERICENTER: Mean argument of periapsis (degrees)
  • MEAN_ANOMALY: Mean anomaly — position along the orbit (degrees)

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Mean vs Osculating Elements

Orbital elements come in two flavors:
  • Osculating elements (used by OPM): Describe the instantaneous orbit at an exact moment. They include all short-period perturbation effects and change rapidly over an orbital period.
  • Mean elements (used by OMM): Averaged to remove short-period oscillations. They describe the “average” orbit and change slowly over time.
VALAR converts osculating state vectors to mean elements using DSST (Draper Semi-analytical Satellite Theory), which analytically removes short-period effects from the osculating state.
Mean elements are more stable for catalog comparison and conjunction screening because they don’t fluctuate with each orbital period. Use OMM when you need to share orbital state in a format comparable to TLE data.
OMM can optionally include parameters for SGP4/SDP4 propagation compatibility:
  • EPHEMERIS_TYPE: Propagation model identifier (0 = SGP4)
  • NORAD_CAT_ID: NORAD catalog number
  • ELEMENT_SET_NO: Element set number
  • REV_AT_EPOCH: Revolution number at epoch
  • BSTAR: SGP4 drag-like coefficient (1/Earth radii)
  • MEAN_MOTION_DOT: First derivative of mean motion (rev/day²)
  • MEAN_MOTION_DDOT: Second derivative of mean motion (rev/day³)

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Common Use Cases

  • Catalog Data Exchange: Sharing mean orbital elements in a structured CCSDS format (alternative to TLE)
  • Conjunction Screening: Providing stable orbital state for collision assessment
  • Interoperability: Exchanging orbital data with agencies and operators using mean-element-based workflows
  • Archival: Storing mean orbital state snapshots for historical reference
Complete definition of the OMM standard in CCSDS 502.0-B-3 (same blue book as OPM and OEM).
Here is a sample OMM file in KVN format: 
CCSDS_OMM_VERS       = 2.0
CREATION_DATE        = 2024-06-15T12:30:00.000
ORIGINATOR           = VALAR

OBJECT_NAME          = SPACECRAFT-ALPHA
OBJECT_ID            = 2023-001A
CENTER_NAME          = EARTH
REF_FRAME            = GCRF
TIME_SYSTEM          = UTC
MEAN_ELEMENT_THEORY  = DSST

EPOCH                = 2024-06-15T00:00:00.000
SEMI_MAJOR_AXIS      = 42164.170 [km]
ECCENTRICITY         = 0.0001456
INCLINATION          = 0.0520 [deg]
RA_OF_ASC_NODE       = 75.1234 [deg]
ARG_OF_PERICENTER    = 180.4567 [deg]
MEAN_ANOMALY         = 90.7890 [deg]
FeatureOMMOPMTLE
Element TypeMean KeplerianOsculating Cartesian/Kepl.Mean Keplerian
Temporal ScopeSingle epochSingle epochSingle epoch
Mean TheoryDSST, SGP4, or otherN/A (osculating)SGP4/SDP4 only
FormatCCSDS KVN/XMLCCSDS KVN/XMLFixed 69-char lines
Reference FrameAny CCSDS frameAny CCSDS frameTEME only
CovarianceOptionalOptionalNot supported
Primary Use CaseCatalog exchangeState snapshots, OD outputPublic catalog distribution

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Export in VALAR

You can export any state vector as OMM directly from the platform:
  1. Navigate to State Vectors → Data
  2. Select a state vector from the list
  3. In the details panel, click the actions menu (three-dot icon)
  4. Select Download OMM
VALAR automatically converts the osculating state vector to mean elements using DSST and generates a CCSDS OMM v2.0 file with default settings (UTC time system, GCRF reference frame).
For more details on working with state vectors, see the State Vectors documentation.