TLE ( abbreviation from English. T wo l ine e lement set , two-line set of elements) is a two-line data format , which is a set of orbit elements for the Earth satellite.
The TLE format was determined by the NORAD constellation and, accordingly, is used in NORAD, NASA and other systems that use the NORAD constellation data to determine the position of space objects of interest.
The SGP4 / SDP4 / SDP8 [1] model can use the TLE [2] format to calculate the exact satellite position at a specific time.
Orbital elements are determined for many thousands of space objects from the NORAD database [3] and are freely distributed for further use on the Internet. TLE always consists of two lines of formatted text. In addition, they may be preceded by a line with the name of the object.
Data Format
The following is an example of a TLE for one of the modules of the International Space Station , usually considered station elements.
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
These data are decoded as follows [4] :
- Title (optional string)
| room | Position | Content | Example |
|---|---|---|---|
| one | 01-24 | name of the property | ISS (ZARYA) |
- Line 1 (required)
| room | Position | Content | Example |
|---|---|---|---|
| one | 01-01 | Line number | one |
| 2 | 03-07 | Satellite number in the NORAD database | 25544 |
| 3 | 08-08 | Classification (U = U nclassified - not secret) | U |
| four | 10-11 | International designation (last two digits of the year of launch) | 98 |
| five | 12-14 | International designation (this year's launch number) | 067 |
| 6 | 15-17 | International designation (part of the launch) | A |
| 7 | 19-20 | Year of the era (last two digits) | 08 |
| eight | 21-32 | Epoch time (the whole part is the day number of the year, the fractional part is the part of the day) | 264.51782528 |
| 9 | 34-43 | The first derivative of the average movement (acceleration) divided by two [revolution / day ^ 2] | -.00002182 |
| ten | 45-52 | The second derivative of the average movement, divided by six (it is understood that the number starts with a decimal separator) [revolution / day ^ 3] | 00000-0 |
| eleven | 54-61 | Braking Factor B * (meaning the number starts with a decimal separator) | -11606-4 |
| 12 | 63-63 | Initially - types of ephemeris, now - always the number 0 | 0 |
| 13 | 65-68 | Item Number (Version) | 292 |
| 14 | 69-69 | Modulo 10 checksum | 7 |
- Line 2 (required)
| room | Position | Content | Example |
|---|---|---|---|
| one | 01-01 | Line number | 2 |
| 2 | 03-07 | Satellite number in the NORAD database | 25544 |
| 3 | 09-16 | Inclination in degrees | 51.6416 |
| four | 18-25 | Longitude node in degrees | 247.4627 |
| five | 27-33 | Eccentricity (meaning the number starts with a decimal separator) | 0006703 |
| 6 | 35-42 | Pericenter argument in degrees | 130.5360 |
| 7 | 44-51 | Average anomaly in degrees | 325.0288 |
| eight | 53-63 | Circulation frequency (revolutions per day) (average movement) [revolution / day] | 15.72125391 |
| 9 | 64-68 | Revolution number at the time of the era | 56353 |
| ten | 69-69 | Modulo 10 checksum | 7 |
The checksum of the strings is calculated by adding the significant digits in the string. For each minus sign (-) in the line, 1 is added to the sum. All other characters are ignored. In the resulting amount, the last digit is taken.
It should also be remembered that the perigee argument, inclination, and other classical Kepler elements given by NORAD in two-line elements are calculated using averaging within the framework of a specific model SGP4 or SDP4 [5] [6] and are not Keplerian elements of the osculating orbit .
Values from TLE cannot be directly compared with orbital elements obtained in another model, or used in another model to predict trajectories. [7]
Notes
- ↑ Spacetrack report No. 3 ( http://www.celestrak.com/NORAD/documentation/spacetrk.pdf ) ( http://celestrak.com/ )
- ↑ Celestrak ( http://celestrak.com/ )
- ↑ TLE NORAD data ( http://celestrak.com/NORAD/elements/ )
- ↑ NORAD Two-Line Element Set Format ( http://celestrak.com/NORAD/documentation/tle-fmt.asp )
- ↑ Frequently Asked Questions: Two-Line Element Set Format Archived on September 17, 2012. , Dr. TS Kelso, Satellite Times Volume 4 Number 3 January 1998. ( original )
- ↑ More Frequently Asked Questions Archived on September 18, 2012. , Dr. TS Kelso, Satellite Times, March 1998 ( original ), "or he has two-line element sets that he wants to use in his favorite satellite tracking program. The simple answer is: never do this! ... Elements in two-line "sets of elements are middle elements calculated to fit many observations using a specific model (SGP4 / SDP4 orbital model)."
- ↑ Tech Note # 2 NORAD Propagators and Two Line Element Sets Archived November 21, 2011 on Wayback Machine , December 12, 2001 "Do not use TLEs with other orbit propagators. They are only compatible withthe SGP4, SDP4 and other algorithms used by NORAD . "