Two-line elements
Encyclopedia
A two-line element set (TLE) is a data format used to convey set of orbital elements
that describe the orbit of an earth satellite. A computer program called a model can use the TLE to compute the precise 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. A TLE consists of a title line followed by two lines of formatted text.
)
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
The meaning of this data is as follows:
Title line
LINE 1
LINE 2:
|->
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
The checksums for each line are calculated by adding the numerical digits on that line. One is added to the checksum for each negative sign (−) on that line. All other non-digit 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.
Orbital elements
Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are generally considered in classical two-body systems, where a Kepler orbit is used...
that describe the orbit of an earth satellite. A computer program called a model can use the TLE to compute the precise position of a satellite at a particular time. The TLE is a format specified by NORAD and used by NORAD and NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
. The TLE can be used directly by the SGP4
SGP4
Simplified perturbations models are a set of five mathematical models used to calculate orbital state vectors of satellites and space debris relative to the Earth-centered inertial coordinate system...
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. A TLE consists of a title line followed by two lines of formatted text.
Format
The following is an example of a TLE (for the International Space StationInternational Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
)
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
The meaning of this data is as follows:
Title line
| Field | Columns | Content | Example |
|---|---|---|---|
| 1 | 01–24 | Satellite name | ISS (ZARYA) |
LINE 1
| 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 | −0.00002182 |
| 10 | 45–52 | Second Time Derivative of Mean Motion divided by six (decimal point assumed) | 00000-0 |
| 11 | 54–61 | BSTAR drag term (decimal point assumed) | |
| 12 | 63–63 | The number 0 (Originally this should have been "Ephemeris type") | 0 |
| 13 | 65–68 | Element number | 292 |
| 14 | 69–69 | Checksum (Modulo 10) | 7 |
LINE 2:
The checksums for each line are calculated by adding the numerical digits on that line. One is added to the checksum for each negative sign (−) on that line. All other non-digit characters are ignored.
For a spacecraft in a typical Low Earth orbit
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
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.