Two-Line Element Sets (TLE)
A two-line element set (TLE/2LE) or three-line element set (3LE) are lists of Keplerian (Orbital) Elementsfor 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):
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:
| Column | Description | Example Value |
|---|---|---|
01 | Line number | 1 |
03-07 | Satellite number | 25544 |
08 | Classification (U=Unclassified, C=Classified, S=Secret) | U |
10-11 | International designator (Last two digits of launch year) | 98 |
12-14 | International designator (Launch number of the year) | 067 |
15-17 | International designator (Piece of the launch) | A |
19-20 | Epoch year (last two digits of year) | 08 |
21-32 | Epoch (Day of the year and fractional portion of the day) | 264.51782528 |
34-43 | First time derivative of the mean motion | -.00002182 |
45-52 | Second time derivative of the mean motion | 00000-0 |
54-61 | BSTAR drag term | -11606-4 |
63 | Ephemeris type | 0 |
65-68 | Element number | 292 |
69 | Checksum | 7 |
Finally, the second line can be broken down to the following:
| Column | Description | Example Value |
|---|---|---|
01 | Line number | 2 |
03-07 | Satellite number | 25544 |
09-16 | Inclination (Degrees) | 51.6416 |
18-25 | Right ascension of the ascending node (Degrees) | 247.4627 |
27-33 | Eccentricity | 0006703 |
35-42 | Argument of perigee (Degrees) | 130.5360 |
44-51 | Mean anomaly (Degrees) | 325.0288 |
53-63 | Mean motion (Revolutions per day) | 15.72125391 |
64-68 | Revolution number at epoch | 56353 |
69 | Checksum | 7 |
TLE Datasets
There are several websites which provide two-line element set data for free, updated daily.
Further Reading
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