> ## 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.

# Orbit Mean-elements Message (OMM)

> Working with CCSDS Orbit Mean-elements Message format in VALAR

> For the complete documentation index, see [llms.txt](/llms.txt).

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.

## 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

## 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)

## 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.

<Tip>
  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.
</Tip>

## TLE-Related Parameters

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)

## 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

<Info>
  Complete definition of the OMM standard in [CCSDS 502.0-B-3](https://ccsds.org/Pubs/502x0b3e1.pdf) (same blue book as OPM and OEM).
</Info>

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]
```

## Differences Between OMM and Related Formats

| Feature          | OMM                  | OPM                        | TLE                         |
| ---------------- | -------------------- | -------------------------- | --------------------------- |
| Element Type     | Mean Keplerian       | Osculating Cartesian/Kepl. | Mean Keplerian              |
| Temporal Scope   | Single epoch         | Single epoch               | Single epoch                |
| Mean Theory      | DSST, SGP4, or other | N/A (osculating)           | SGP4/SDP4 only              |
| Format           | CCSDS KVN/XML        | CCSDS KVN/XML              | Fixed 69-char lines         |
| Reference Frame  | Any CCSDS frame      | Any CCSDS frame            | TEME only                   |
| Covariance       | Optional             | Optional                   | Not supported               |
| Primary Use Case | Catalog exchange     | State snapshots, OD output | Public catalog distribution |

## 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).

<Info>
  For more details on working with state vectors, see the [State Vectors documentation](/features/state-vectors).
</Info>