TLE File format documentation

By using (by permission) code derived from XEphem the MMT can now track (or attempt to track) earth orbiting satellites. It should be noted though, that satellites in low earth orbit may require tracking speeds beyond what our telescope can safely produce, and may be challenging or impossible to acquire and track by our control system for other reasons.

Another excellent discussion of the TLE format and orbital parameters may be found at: orbitessera. Note that although these are called two line elements, the inclusion of a line with the object name makes each entry take up 3 lines in the file.

Two-line Earth satellite element (TLE) sets

The MMT supports reading files which contain Earth satellite orbits defined using the the NORAD "two-line element" set format, or TLE. Because the TLE format is quite rigid and includes a checksum within each line, it is possible to search files containing other arbitrary text and find each properly formatted TLE contained therein. Follows is a description of the TLE. Note the line immediately preceding the TLE, line "0", is assumed to contain a common name for the satellite, this line is only used if the following two lines conform to TLE.

Data for each satellite consists of three lines in the following format:

Line 0 is a twenty-four character name.

Lines 1 and 2 are the standard Two-Line Orbital Element Set Format identical to that used by NORAD and NASA. The format description is:

Line 1
Column Description
01 Line Number of Element Data
03-07 Satellite Number
08 Classification (U=Unclassified)
10-11 International Designator, last two digits of launch year,  2000+ if < 57.
12-14 International Designator, launch number of the year
15-17 International Designator, piece of the launch
19-20 Epoch Year, last two digits of year,  2000+ if < 57
21-32 Epoch Day of the year and fractional portion of the day
34-43 First Time Derivative of the Mean Motion
45-52 Second Time Derivative of Mean Motion (decimal point assumed)
54-61 BSTAR drag term (decimal point assumed)
63 Ephemeris type
65-68 Element number
69 Checksum (Modulo 10)
(Letters, blanks, periods, plus signs = 0; minus signs = 1)

Line 2
Column Description
01 Line Number of Element Data
03-07 Satellite Number
09-16 Inclination [Degrees]
18-25 Right Ascension of the Ascending Node [Degrees]
27-33 Eccentricity (decimal point assumed)
35-42 Argument of Perigee [Degrees]
44-51 Mean Anomaly [Degrees]
53-63 Mean Motion [Revs per day]
64-68 Revolution number at epoch [Revs]
69 Checksum (Modulo 10)