> ## Documentation Index
> Fetch the complete documentation index at: https://docs.rotastellar.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Propagate Trajectory

> Generate full satellite trajectory as a time series over up to 48 hours

<Note>
  **Base URL:** `https://sim.rotastellar.com`
  — No API key required.
</Note>

## Request

<ParamField body="elements" type="object" required>
  Orbital elements. See [Orbital Elements](/sim/overview#orbital-elements).
</ParamField>

<ParamField body="start" type="string">
  ISO 8601 start time. Defaults to current time.
</ParamField>

<ParamField body="end" type="string">
  ISO 8601 end time. Default: start + 6 hours. Max window: 48 hours.
</ParamField>

<ParamField body="step_s" type="number">
  Seconds between trajectory points. Default: 60. Max 5,000 total points.
</ParamField>

<RequestExample>
  ```bash theme={null}
  curl -X POST https://sim.rotastellar.com/v1/propagate \
    -H "Content-Type: application/json" \
    -d '{
      "elements": {
        "altitude_km": 550,
        "inclination_deg": 53
      },
      "start": "2026-03-08T12:00:00Z",
      "end": "2026-03-08T14:00:00Z",
      "step_s": 60
    }'
  ```
</RequestExample>

<ResponseExample>
  ```json 200 OK theme={null}
  {
    "trajectory": [
      {
        "t": "2026-03-08T12:00:00Z",
        "lat": 42.15,
        "lon": -73.82,
        "altitude_km": 550.3,
        "velocity_km_s": 7.59,
        "in_eclipse": false,
        "orbit_fraction": 0.000
      },
      {
        "t": "2026-03-08T12:01:00Z",
        "lat": 42.58,
        "lon": -72.14,
        "altitude_km": 550.3,
        "velocity_km_s": 7.59,
        "in_eclipse": false,
        "orbit_fraction": 0.010
      }
    ],
    "count": 121,
    "start": "2026-03-08T12:00:00Z",
    "end": "2026-03-08T14:00:00Z",
    "step_s": 60
  }
  ```

  ```json 400 Range Too Large theme={null}
  {
    "error": "range_too_large",
    "message": "Propagation window exceeds 48 hours"
  }
  ```
</ResponseExample>

## Constraints

| Constraint     | Limit      |
| -------------- | ---------- |
| Max window     | 48 hours   |
| Max points     | 5,000      |
| Default step   | 60 seconds |
| Default window | 6 hours    |