TLE Structure

This page gives a column-by-column description of the Two-line Element Set structure. These tables should help those writing computer software intended to read or write this format. This complements the illustration on the TLE Format page.

TLE Line-1 Structure

Col(s)

Field

Range

Units

Comments

1

Line Number

1

-

Identifies Line 1

2

blank space

-

-

Invariant

3 - 7

Catalog Number

1 - 99999

-

Sequential Sat ID

8

Classification

U, C, S

-

Always Unclassified for Publicly-released TLEs

9

blank space

-

-

Invariant

10 - 17

International Designator

-

-

  • cols 10 to 11 - 2-digit year
  • cols 12 to 14 - launch number
  • cols 15 to 17 - piece ID

18

blank space

-

-

Invariant

19 - 32

Epoch Time

-

-

  • cols 19 to 20 - 2-digit year
  • cols 21 to 23 - day of year
  • col 24 - decimal point
  • cols 25 to 32 - fraction of day

33

blank space

-

-

Invariant

34 - 43

ndot/2

-0.99999999 to 0.99999999

rev/day2

  • col 34 - sign (negative or blank)
  • col 35 - decimal point
  • cols 36 to 43 - mantissa

44

blank space

-

-

Invariant

45 - 52

nddot/6

-

rev/day3

  • col 45 - sign
  • cols 46 to 50 - mantissa (implied leading decimal point)
  • col 51 - tens exponent sign (always negative)
  • col 52 - tens exponent

53

blank space

-

-

Invariant

54 - 61

Bstar

-

1 / Earth Radii

  • col 54 - sign
  • cols 55 to 59 - mantissa (implied leading decimal point)
  • col 60 - tens exponent sign (always negative)
  • col 61 - tens exponent

62

blank space

-

-

Invariant

63

Ephemeris Type

0 - 7

-

Always 0 for Publicly- Released TLEs

64

blank space

-

-

Invariant

65 - 68

Element Number

1 - 9999

-

Incremented with each update

69

Check Sum

0 - 9

-

Modulo-10

This page should be helpful if you want to write software to read or write Keplerian TLEs

The tables describe the structure of lines 1 and 2 in detail

The far left describes the columns allocated for each value

The second column tells you what the value describes

The third column gives you any applicable range of values

The fourth column gives you the units of measure

Top

TLE Line 2 Structure

Col(s)

Fields

Range

Units

Comments

1

Line Number

2

-

Identifies Line 2

2

blank space

-

-

Invariant

3 - 7

Catalog Number

1 - 99999

-

Must be the Same as cols 3 - 7 for Line 1

8

blank space

-

-

Invariant

9 - 16

Inclination

0.0000 to 180.0000

degrees

col 12 is the decimal point

17

blank space

-

-

Invariant

18 - 25

Right Ascension of the Ascending Node

0.0000 to 359.9999

degrees

col 21 is the decimal point

26

blank space

-

-

Invariant

27 - 33

Eccentricity

0000010 - 9500000

-

decimal point is implied between cols 26 and 27

34

blank space

-

-

Invariant

35 - 42

Argument of Perigee

0.0000 - 359.9999

degrees

col 38 is the decimal point

43

blank space

-

-

Invariant

44 - 51

Mean Anomaly

0.0000 - 359.9999

degrees

col 47 is the decimal point

52

blank space

-

-

Invariant

53 - 63

Mean Motion

-

rev/day

col 55 is the decimal point

64 - 68

Revolution Number

1 - 99999

-

rev increments at each ascending node

69

Check Sum

0 - 9

-

Modulo-10

Top

The far left describes the columns allocated for each value

The second column tells you what the value describes

The third column gives you any applicable range of values

The fourth column gives you the units of measure