From Wikipedia, the free encyclopedia  View original article
A twoline element set (TLE) is a data format used to convey sets of orbital elements that describe the orbits of Earthorbiting satellites. A computer program called a model can use the TLE to compute the position of a satellite at a particular time. The TLE is a format specified by NORAD and used by NORAD and NASA. The TLE can be used directly by the SGP4 model (or one of the SGP8, SDP4, SDP8 models). Orbital elements are determined for many thousands of space objects by NORAD and are freely distributed on the Internet in the form of TLEs.^{[1]} A TLE consists of a title line followed by two lines of formatted text.
The following is an example of a TLE (for the International Space Station)
ISS (ZARYA) 1 25544U 98067A 08264.51782528 .00002182 000000 116064 0 2927 2 25544 51.6416 247.4627 0006703 130.5360 325.0288 15.72125391563537
The meaning of this data is as follows:
Field  Columns  Content  Example 

1  01–24  Satellite name  ISS (ZARYA) 
Field  Columns  Content  Example 

1  01–01  Line number  1 
2  03–07  Satellite number  25544 
3  08–08  Classification (U=Unclassified)  U 
4  10–11  International Designator (Last two digits of launch year)  98 
5  12–14  International Designator (Launch number of the year)  067 
6  15–17  International Designator (Piece of the launch)  A 
7  19–20  Epoch Year (Last two digits of year)  08 
8  21–32  Epoch (Day of the year and fractional portion of the day)  264.51782528 
9  34–43  First Time Derivative of the Mean Motion divided by two ^{[2]}  −.00002182 
10  45–52  Second Time Derivative of Mean Motion divided by six (decimal point assumed)  000000 
11  54–61  BSTAR drag term (decimal point assumed) ^{[2]}  116064 
12  63–63  The number 0 (Originally this should have been "Ephemeris type")  0 
13  65–68  Element set number. incremented when a new TLE is generated for this object. ^{[2]}  292 
14  69–69  Checksum (Modulo 10)  7 
Field  Columns  Content  Example 

1  01–01  Line number  2 
2  03–07  Satellite number  25544 
3  09–16  Inclination [Degrees]  51.6416 
4  18–25  Right Ascension of the Ascending Node [Degrees]  247.4627 
5  27–33  Eccentricity (decimal point assumed)  0006703 
6  35–42  Argument of Perigee [Degrees]  130.5360 
7  44–51  Mean Anomaly [Degrees]  325.0288 
8  53–63  Mean Motion [Revs per day]  15.72125391 
9  64–68  Revolution number at epoch [Revs]  56353 
10  69–69  Checksum (Modulo 10)  7 
Where decimal points are assumed, they are leading decimal points. The last two symbols in Fields 10 and 11 of the first line give powers of 10 to apply to the preceding decimal. Thus, for example, Field 11 (116064) translates to 0.11606E4.
The checksums for each line are calculated by adding the all numerical digits on that line, including the line number. One is added to the checksum for each negative sign (−) on that line. All other nondigit characters are ignored.
For a spacecraft in a typical Low Earth orbit the accuracy that can be obtained with the SGP4 orbit model is on the order of 1 km within a few days of the epoch of the element set.^{[3]}
