Four-line Elements serve the same purpose as Two-Line Elements, to provide information about the orbit of a spacecraft in order to allow a prediction of its position at some time in the near future.
Data for each satellite consists of four lines in the following format. A blank line may separate multiple entries in a file.
AAAAA BBBBBBBBBBBBBBB CCCCC DDDDDDDDDDDD EEEEEEEEE FFFFFFFFFFFF GGGGGGGGGGGGG HHHHHHHHHHHHH IIIIIIIIIIIII JJJJJJJJJJ KKK LLL MMM NNNNN OOOOOOOOOOO PPPPPPPPPPPP QQQQQ RRRRRRRRRR SSSSSSSSSS
| Line | Symbol | Field | Field name and description |
|---|---|---|---|
| Line 1 | A | 1-5 | Satellite number |
| B | 7-21 | Epoch time | |
| C | 23-27 | Epoch REV number | |
| D | 29-40 | X-component of the position vector at epoch in kilometers | |
| E | 42-53 | Y-component of the position vector at epoch in kilometers | |
| Line 2 | F | 1-12 | Z-component of the position vector at epoch in kilometers |
| G | 14-26 | X-component of the velocity vector at epoch in kilometers/second | |
| H | 28-40 | Y-component of the velocity vector at epoch in kilometers/second | |
| I | 42-54 | Z-component of the velocity vector at epoch in kilometers/second | |
| Line 3 | J | 1-10 | Ballistic coefficient (CDA/m) units m2/kg |
| K | 12-14 | Daily solar flux at 10.7 cm (F10) units 10-E07 watts/m2 | |
| L | 16-18 | Average solar flux for 90 days at 10.7 cm units 10-E07 watts/m2 (F10 AV) | |
| M | 20-22 | Planetary magnetic index (AP) units 2x10-E05 gauss | |
| N | 25-29 | Drag modulation coefficient (MBETA) | |
| O | 32-42 | Radiation pressure coefficient (AGOM) | |
| P | 46-57 | Time of Ascending node in days since the beginning of the current year, Jan. 0, 0Z | |
| Q | 60-64 | REV number corresponding to P above | |
| Line 4 | R | 1-10 | Universal time correction in seconds |
| S | 13-22 | Universal time correction rate in milliseconds/day |
Example:
21263 94121200000.000 15390 -5956.862381 2857.146928 -2846.166214 -2.08615086 2.34822491 6.75149989 0.06822045 75 89 25 .9449 .0000500000 121.90827566 15392 -0.105845 -2.796000
Four-line elements are available from http://www1.ncdc.noaa.gov/pub/data/orbit/4line/
See also the Two-Line Elements Set Format and the Improved Inter-Range Vector format.
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