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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