> ## 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.

# Ephemeris Generation

> Generate OEM files from state vectors for mission planning and data sharing

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

Generate OEM (Orbit Ephemeris Message) files from state vectors. OEM files contain predicted satellite positions over a specified time range, useful for mission planning, conjunction analysis, or sharing with external systems.

**Access:** Click **Generate Ephemerides** on the State Vectors page top-right corner.

## Modal Overview

The Generate Ephemerides modal guides you through four steps:

<img src="https://mintlify.s3.us-west-1.amazonaws.com/valar-8bbb18b5/images/ephemerides-generation.png" alt="Ephemerides Generation" title="Ephemerides Generation" className="mx-auto" style={{ width:"77%" }} />

## Step 1: State Vector Selection

### Select Spacecraft

Choose a spacecraft from the dropdown. The list shows spacecraft names with colored satellite icons.

### Select State Vector

After selecting a spacecraft, choose a state vector from the dropdown. Each option shows the state vector ID and epoch date/time.

**Empty State:** If no state vectors are available for the selected spacecraft in the last 30 days, you can:

* Click **Import State Vector** to open the import dialog
* Click **Run Orbit Determination** to configure OD

### Include Covariance Data

Toggle whether to include covariance matrix in the OEM file:

| Option  | Effect                                                                   |
| ------- | ------------------------------------------------------------------------ |
| **Yes** | Includes covariance matrix; enables covariance frame selection in Step 3 |
| **No**  | Excludes covariance data (default)                                       |

## Step 2: Time Range Configuration

### Time Step

Use the slider to set the interval between data points (1–60 minutes).

* Smaller step = more data points, larger file
* Larger step = fewer data points, smaller file

### Start Date & Time

Select the start date from the 7-day calendar (use arrows to navigate weeks) and enter the start time in 24-hour UTC format (e.g., "08:30").

**Default:** 00:00 UTC

### End Date & Time

Select the end date and enter the end time.

**Default:** 23:59 UTC

<Info>
  Dates are limited to ±30 days from the state vector epoch. Total duration cannot exceed 30 days.
</Info>

## Step 3: Reference Frames

### Time System

| Value   | Description                          |
| ------- | ------------------------------------ |
| **UTC** | Coordinated Universal Time (default) |
| **TAI** | International Atomic Time            |
| **TT**  | Terrestrial Time                     |
| **TDB** | Barycentric Dynamical Time           |
| **TCG** | Geocentric Coordinate Time           |
| **TCB** | Barycentric Coordinate Time          |
| **GPS** | GPS Time                             |

### Ephemerides Reference Frame

| Value       | Description                                    |
| ----------- | ---------------------------------------------- |
| **GCRF**    | Geocentric Celestial Reference Frame (default) |
| **EME2000** | Earth Mean Equator and Equinox of J2000        |
| **ITRF**    | International Terrestrial Reference Frame      |
| **TOD**     | True of Date                                   |
| **MOD**     | Mean of Date                                   |
| **TEME**    | True Equator Mean Equinox                      |

### Covariance Reference Frame

Only available when covariance is enabled in Step 1.

| Value   | Description                        |
| ------- | ---------------------------------- |
| **RTN** | Radial-Tangential-Normal (default) |
| **TNW** | Tangential-Normal-Out-of-plane     |

## Step 4: Review & Generate

Review your configuration before generating:

**State Vector Card**

* Spacecraft name
* State Vector ID
* Epoch date and time

**Time Range Card**

* Start and end date/time (UTC)
* Time step in minutes
* Calculated number of data points

**Reference Frames Card**

* Time system
* Ephemerides frame
* Covariance frame (if enabled)

Click the **Edit** button (pencil icon) on any card to jump back to that step.

### Generate OEM

Click **Generate OEM** to create and download the file.

**Loading states:**

1. "Sending request to server..."
2. "Downloading file..."

**On success:**

* Toast notification: "OEM generated successfully"
* File downloads automatically
* Modal closes

## Navigation

* **Step tabs**: Click any step name to jump directly to it
* **Next**: Validates current step and proceeds
* **Back**: Returns to previous step (hidden on Step 1)
* **Cancel**: Closes modal without generating

## Error Handling

| Error              | Message                                                      |
| ------------------ | ------------------------------------------------------------ |
| 422 (Validation)   | Field-specific messages from server                          |
| 400 (Bad Request)  | "Please check your configuration"                            |
| 404 (Not Found)    | "The state vector may have been deleted"                     |
| 500 (Server Error) | "An error occurred during OEM generation. Please try again." |

## Output

**Format:** OEM (Orbit Ephemeris Message), CCSDS standard text format

**Filename:** `oem_{stateVectorId}_{timestamp}.txt`

## Constraints

| Constraint            | Value      |
| --------------------- | ---------- |
| Date range from epoch | ±30 days   |
| Maximum duration      | 30 days    |
| Minimum time step     | 1 minute   |
| Maximum time step     | 60 minutes |

## Related Pages

* [State Vectors](/features/state-vectors): Manage orbit solutions and state vectors
* [OEM Format](/file-formats/oem): OEM file format specification