> For the complete documentation index, see [llms.txt](https://aerospace.jamiepegg.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://aerospace.jamiepegg.com/osint-and-reconnaissance/satellite-telemetry/two-line-element-sets-tle.md).

# Two-Line Element Sets (TLE)

A two-line element set (TLE/2LE) or three-line element set (3LE) are lists of [Keplerian (Orbital) Elements](/aerospace-fundamentals/keplerian-orbital-elements.md) for satellites orbiting the earth at a given point in time, the epoch.

The TLE, alongside a suitable prediction formula, can be utilised to calculate the position and velocity of a satellite at any point in the past or future.

## Format

Take the following two-line element set for the International Space Station (ISS):

```
ISS (ZARYA)
1 25544U 98067A   08264.51782528 -.00002182  00000-0 -11606-4 0  2927
2 25544  51.6416 247.4627 0006703 130.5360 325.0288 15.72125391563537
```

Considering the above example, the TLE can be broken down line-by-line. First, an optional title line is present, in our instance `ISS (ZARYA)`. Following this, the first line can be broken down as follows:

<table><thead><tr><th width="124">Column</th><th width="477">Description</th><th>Example Value</th></tr></thead><tbody><tr><td>01</td><td>Line number</td><td>1</td></tr><tr><td>03-07</td><td>Satellite number</td><td>25544</td></tr><tr><td>08</td><td>Classification (U=Unclassified, C=Classified, S=Secret)</td><td>U</td></tr><tr><td>10-11</td><td>International designator (Last two digits of launch year)</td><td>98</td></tr><tr><td>12-14</td><td>International designator (Launch number of the year)</td><td>067</td></tr><tr><td>15-17</td><td>International designator (Piece of the launch)</td><td>A</td></tr><tr><td>19-20</td><td>Epoch year (last two digits of year)</td><td>08</td></tr><tr><td>21-32</td><td>Epoch (Day of the year and fractional portion of the day)</td><td>264.51782528</td></tr><tr><td>34-43</td><td>First time derivative of the mean motion</td><td>-.00002182</td></tr><tr><td>45-52</td><td>Second time derivative of the mean motion</td><td>00000-0</td></tr><tr><td>54-61</td><td>BSTAR drag term</td><td>-11606-4</td></tr><tr><td>63</td><td>Ephemeris type</td><td>0</td></tr><tr><td>65-68</td><td>Element number</td><td>292</td></tr><tr><td>69</td><td>Checksum</td><td>7</td></tr></tbody></table>

Finally, the second line can be broken down to the following:

<table><thead><tr><th width="124">Column</th><th width="477">Description</th><th>Example Value</th></tr></thead><tbody><tr><td>01</td><td>Line number</td><td>2</td></tr><tr><td>03-07</td><td>Satellite number</td><td>25544</td></tr><tr><td>09-16</td><td>Inclination (Degrees)</td><td>51.6416</td></tr><tr><td>18-25</td><td>Right ascension of the ascending node (Degrees)</td><td>247.4627</td></tr><tr><td>27-33</td><td>Eccentricity</td><td>0006703</td></tr><tr><td>35-42</td><td>Argument of perigee (Degrees)</td><td>130.5360</td></tr><tr><td>44-51</td><td>Mean anomaly (Degrees)</td><td>325.0288</td></tr><tr><td>53-63</td><td>Mean motion (Revolutions per day)</td><td>15.72125391</td></tr><tr><td>64-68</td><td>Revolution number at epoch</td><td>56353</td></tr><tr><td>69</td><td>Checksum</td><td>7</td></tr></tbody></table>

## TLE Datasets

There are several websites which provide two-line element set data for free, updated daily.

* <https://www.space-track.org/>
* <https://celestrak.org/>

## Further Reading

{% embed url="<https://en.wikipedia.org/wiki/Two-line_element_set>" %}

{% embed url="<https://celestrak.org/NORAD/documentation/tle-fmt.php>" %}


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://aerospace.jamiepegg.com/osint-and-reconnaissance/satellite-telemetry/two-line-element-sets-tle.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.