Two-Line Element Sets (TLE)
A two-line element set (TLE/2LE) or three-line element set (3LE) are lists of Keplerian (Orbital) Elements 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):
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:
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:
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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