Two-line element set

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.

Format

The following is an example of a TLE (for the International Space Station)

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)	-11606-4
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

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.