TLE File Format (*.tce /*.tle)
A TLE file is an ASCII text file that contains of a listing of two-line element sets as provided by the U.S. Strategic Command (USSTRATCOM) and ends in a .tle or .tce extension. TLE sets are used by the Simplified General Perturbation (SGP4) propagator within STK.
TLE Format Validation
By default, STK will validate each line of a TLE to detect for possibly bad input to prevent misreading values. To turn the TLE Validator off, edit the _Default.ap file, located in the Defaults directory, using a text editor (for example, Notepad or WordPad):
In the line of the file after BEGIN TLEValidation, set the value for Validator to Off.
By turning the validator off, STK is trusting that you format the TLE correctly, at least for extracting the computational data in the TLE. STK uses a fixed-read format, reading the specific columns as indicated in the TLE format, for extracting all of the TLE data. An improperly formatted TLE (for example, misalignment of the columns) may not be read correctly by STK.
The following tables describe the TLE file format and format validation performed.
Line 1
| Column |
Description |
Format Validation |
| 1 |
Card number |
Must be 1.
|
| 2 |
Blank |
Must be a blank space. |
| 3-7 |
Satellite or USSTRATCOM number |
3-6 must be either an alphanumeric character or a blank space.
7 must be an alphanumeric character.
|
| 8 |
Security classification |
No validation performed. |
| 9 |
Blank |
Must be a blank space |
| 10-17 |
International number |
No validation performed. |
| 18 |
Blank |
Must be a blank space. |
| 19-20 |
Epoch Year |
Must be a digit [0-9].
|
| 21-32 |
Epoch day to eight decimal places |
21-23 must be a digit [0-9]. The value of this 3-digit integer must not be greater than 366.
24 must be a period (.). 25-32 must be a digit [0-9].
|
| 33 |
Blank |
33 must be a blank space.
|
| 34-43 |
N/2 - Revolutions per day squared |
34 must be either - or + or 0 or a blank space.
35 must be a period (.).
36-43 must be a digit [0-9]. |
| 44 |
Blank |
Must be a blank space. |
| 45-52 |
N/6 - Revolutions per day cubed |
45 must be either - or + or a blank space.
46-50 must be a digit [0-9].
51 must be either - or + or a blank space 52 must be either a digit [0-9] or a blank space. |
| 53 |
Blank |
Must be a blank space. |
| 54-61 |
Bstar drag |
54 must be either - or + or a blank space.
55-59 must be a digit [0-9].
60 must be either - or + or a blank space. 61 must be either a digit [0-9] or a blank space. |
| 62 |
Blank |
Must be a blank space. |
| 63 |
Ephemeris |
Must be either a digit [0-9] or a blank space. |
| 64 |
Blank |
Must be a blank space. |
| 65-68 |
Element set number |
65-67 must be either a digit [0-9] or a blank space.
68 must be a digit [0-9] |
| 69 |
CheckSum Value |
No validation performed. |
Line 2
| Column |
Description |
Format Validation |
| 1 |
Card number |
Must be 2.
|
| 2 |
Blank |
Must be a blank space.
|
| 3-7 |
Satellite or USSTRATCOM number |
3-6 must be either an alphanumeric character or a blank space.
7 must be either an alphanumeric character.
|
| 8 |
Blank |
Must be a blank space. |
| 9-16 |
Inclination (degrees) |
Determines the inclination value. Valid values are 0.0 through 180.0.
9-11 must be either a digit [0-9] or a blank space. 12 must be a period (.). 13-16 must be a digit [0-9].
|
| 17 |
Blank |
Must be a blank space. |
| 18-25 |
Right ascension of node (degrees) |
Determines the RAAN value. Valid values are 0.0 through 360.0.
18-20 must be either a digit [0-9] or a blank space.
21 must be a period (.).
22-25 must be a digit [0-9].
|
| 26 |
Blank |
26 must be a blank space.
|
| 27-33 |
Eccentricity (decimal point understood) |
Must be a digit [0-9].
|
| 34 |
Blank |
Must be a blank space. |
| 35-42 |
Argument of perigee (degrees) |
Determines the argument of perigee value. Valid values are 0.0 through 360.0.
35-37 must be either a digit [0-9] or a blank space.
38 must be a period (.).
39-42 must be a digit [0-9].
|
| 43 |
Blank |
Must be a blank space. |
| 44-51 |
Mean anomaly (degrees) |
Determines the mean anomaly value. Valid values are 0.0 through 360.0.
44-46 must be either a digit [0-9] or a blank space.
47 must be a period (.).
48-51 must be a digit [0-9].
|
| 52 |
Blank |
Must be a blank space. |
| 53-63 |
Mean motion (revolutions per day)
|
Determines the mean motion value. The value must not be greater than 17.0.
53-54 must be either a digit [0-9] or a blank space.
55 must be a period (.).
56-63 must be a digit [0-9].
|
| 64-68 |
Revolution number at epoch |
64-67 must be either a digit [0-9] or a blank space.
68 must be a digit [0-9]. |
| 69 |
CheckSum Value |
No validation performed. |
Blank columns are checked to help with identifying misalignment of values in the TLE (that is, dropping columns).