> ## Documentation Index > Fetch the complete documentation index at: https://docs.valar.space/llms.txt > Use this file to discover all available pages before exploring further. # OEM (Orbit Ephemeris Message) > Working with CCSDS Orbit Ephemeris Message format in VALAR > For the complete documentation index, see [llms.txt](/llms.txt). The Orbit Ephemeris Message (OEM) is a standardized ASCII text format for exchanging spacecraft position and velocity data over time. Each OEM file contains a time-ordered series of state vectors (ephemeris points) that define a spacecraft's trajectory, enabling precise orbit propagation and prediction. ## Key Components An OEM file contains several distinct sections: * **Header**: File-level metadata including format version, creation date, and originator information * **Metadata**: Orbital context information such as object identification, reference frame, time system, and interpolation specifications * **Ephemeris Data**: Time-ordered state vectors containing position (X, Y, Z) and velocity (VX, VY, VZ) at specific epochs * **Covariance (Optional)**: Position and velocity uncertainty matrices for each ephemeris point ## Critical Fields ### Metadata Section * **OBJECT\_NAME / OBJECT\_ID**: Spacecraft identification * **REF\_FRAME**: Coordinate reference frame (e.g., EME2000, ITRF2000) * **TIME\_SYSTEM**: Time system used (e.g., UTC, TAI) * **START\_TIME / STOP\_TIME**: Temporal bounds of ephemeris data * **INTERPOLATION**: Method for interpolating between points (e.g., Hermite, Lagrange) * **INTERPOLATION\_DEGREE**: Polynomial degree for interpolation (typically 7-8) ### Ephemeris Data Format Each line contains: `Epoch X Y Z VX VY VZ` * **Epoch**: UTC timestamp * **X, Y, Z**: Position components in kilometers * **VX, VY, VZ**: Velocity components in km/s ## Common Use Cases * **Conjunction Assessment**: Sharing precise trajectories for collision avoidance analysis * **Maneuver Planning**: Baseline trajectories for delta-V calculations * **Mission Coordination**: Exchanging orbit information between control centers * **Orbit Propagation**: High-fidelity trajectory propagation using interpolation * **Ground Track Visualization**: Displaying spacecraft position over time Complete definition of the OEM standard on [CCSDS 502.0-B-3](https://ccsds.org/Pubs/502x0b3e1.pdf) guidelines. Here is a sample OEM file in KVN format: ``` CCSDS_OEM_VERS = 2.0 CREATION_DATE = 2024-06-15T08:30:00.000 ORIGINATOR = VALAR META_START OBJECT_NAME = SPACECRAFT-1 OBJECT_ID = 2023-001A CENTER_NAME = EARTH REF_FRAME = EME2000 TIME_SYSTEM = UTC START_TIME = 2024-06-15T00:00:00.000 STOP_TIME = 2024-06-16T00:00:00.000 USEABLE_START_TIME = 2024-06-15T00:00:00.000 USEABLE_STOP_TIME = 2024-06-16T00:00:00.000 INTERPOLATION = HERMITE INTERPOLATION_DEGREE = 7 META_STOP COMMENT Ephemeris generated from OD solution COMMENT State vectors in EME2000 reference frame 2024-06-15T00:00:00.000 6655.994 -40218.575 -82.918 3.115482 0.470426 -0.001015 2024-06-15T01:00:00.000 6892.441 -39845.123 -76.234 3.087234 0.501287 -0.000923 2024-06-15T02:00:00.000 7112.873 -39458.892 -69.445 3.058012 0.531456 -0.000831 2024-06-15T03:00:00.000 7316.234 -39060.234 -62.567 3.027856 0.560847 -0.000738 2024-06-15T04:00:00.000 7501.567 -38649.512 -55.612 2.996812 0.589382 -0.000645 2024-06-15T05:00:00.000 7668.012 -38227.123 -48.593 2.964923 0.616989 -0.000551 2024-06-15T06:00:00.000 7814.789 -37793.478 -41.523 2.932234 0.643598 -0.000457 2024-06-15T07:00:00.000 7941.234 -37349.012 -34.415 2.898789 0.669142 -0.000362 2024-06-15T08:00:00.000 8046.678 -36894.189 -27.281 2.864634 0.693559 -0.000267 COVARIANCE_START EPOCH = 2024-06-15T00:00:00.000 COV_REF_FRAME = EME2000 CX_X = 4.142e+01 CY_X = -8.579e+00 CY_Y = 5.189e+01 CZ_X = -4.788e+01 CZ_Y = -4.472e+01 CZ_Z = 5.960e+01 CX_DOT_X = 3.523e-03 CX_DOT_Y = 1.045e-03 CX_DOT_Z = -1.234e-03 CX_DOT_X_DOT = 8.945e-07 CY_DOT_X = -2.678e-03 CY_DOT_Y = -5.234e-04 CY_DOT_Z = 1.876e-03 CY_DOT_X_DOT = -3.456e-07 CY_DOT_Y_DOT = 7.234e-07 CZ_DOT_X = -1.234e-03 CZ_DOT_Y = 2.345e-03 CZ_DOT_Z = -8.765e-04 CZ_DOT_X_DOT = 2.134e-07 CZ_DOT_Y_DOT = -4.567e-07 CZ_DOT_Z_DOT = 6.789e-07 COVARIANCE_STOP ``` ## Interpolation Methods OEM files support multiple interpolation methods for computing state vectors between ephemeris points: * **Hermite**: Uses both position and velocity for smooth interpolation (most common) * **Lagrange**: Position-only polynomial interpolation * **Linear**: Simple linear interpolation between points The interpolation degree (typically 7-8) determines the polynomial order and affects accuracy versus computational cost.