TLE

TLE

The TLE, or Two Line Elements set, is a data format that contains information about the orbit at a specific epoch of an Earth-orbiting object. The information is split into two lines with 70 characters each. In the following, it is presented an example of a TLE describing the orbit of the Brazilian satellite SCD-1 at 25 December 2018:

SCD 1                   
1 22490U 93009B   18359.76217587  .00000186  00000-0  84512-6 0  9998
2 22490  24.9694 116.1709 0043211  90.3968  62.0083 14.44539396366163

For more information, see https://en.wikipedia.org/wiki/Two-line_element_set.

The TLE contains all the necessary information to propagate the orbit using, for example, the SGP4 orbit propagator. Hence, this package contains a set of functions that helps to load the TLE information to be used in the Orbit propagators.

If the TLEs are stored in one file, then they can be loaded using the function:

function read_tle(tle_filename::String, verify_checksum::Bool = true)

where the tle_filename is the file path. Each TLE line has a checksum to verify the correctness of the data. By default, if the checksum is wrong, then this function will throw an error. The checksum verification can be avoided by setting verify_checksum to false.

This function returns an array of TLEs. Each TLE is an instance of the structure TLE.

julia> tles = read_tle("tles")
2-element Array{TLE,1}:
 TLE: SCD 1 (Epoch = 2018-12-25T18:17:32)
 TLE: SCD 2 (Epoch = 2018-12-26T05:50:03)

julia> tles[1]
                             TLE
    ==========================================================
                            Name: SCD 1
                Satellite number: 22490
        International designator: 93009B
                    Epoch (Year): 18
                     Epoch (Day): 359.76217587
              Epoch (Julian Day): 2458478.26218
              Element set number: 999
                     Inclination:  24.96940000 deg
                            RAAN: 116.17090000 deg
             Argument of perigee:  90.39680000 deg
                    Mean anomaly:  62.00830000 deg
                 Mean motion (n):  14.44539396 revs/day
               Revolution number: 36616

                              B*: 0.000001 1/[er]

                        1   d
                       ---.--- n: 0.000002 rev/day²
                        2  dt

                        1   d²
                       ---.--- n: 0.000000 rev/day³
                        6  dt²
    ==========================================================

julia> tles[2]
                             TLE
    ==========================================================
                            Name: SCD 2
                Satellite number: 25504
        International designator: 98060A
                    Epoch (Year): 18
                     Epoch (Day): 360.24309362
              Epoch (Julian Day): 2458478.74309
              Element set number: 999
                     Inclination:  24.99670000 deg
                            RAAN: 319.86640000 deg
             Argument of perigee: 121.38100000 deg
                    Mean anomaly:   9.79390000 deg
                 Mean motion (n):  14.44057429 revs/day
               Revolution number: 6554

                              B*: 0.000011 1/[er]

                        1   d
                       ---.--- n: 0.000002 rev/day²
                        2  dt

                        1   d²
                       ---.--- n: 0.000000 rev/day³
                        6  dt²
    ==========================================================

If the TLE is stored in a string, then it can be read using the following functions:

function read_tle_from_string(tles::String, verify_checksum::Bool = true)
function read_tle_from_string(tle_l1::String, tle_l2::String, verify_checksum::Bool = false)

In the first case, a list of TLEs can be passed in tles. In the second case, the first line and second line of a TLE can be passed in tle_l1 and tle_l2, respectively. In both cases an array of TLEs is returned. The argument verify_checksum has the same function as described previously.

julia> tles = """
       SCD 1
       1 22490U 93009B   18359.76217587  .00000186  00000-0  84512-6 0  9998
       2 22490  24.9694 116.1709 0043211  90.3968  62.0083 14.44539396366163
       SCD 2
       1 25504U 98060A   18360.24309362  .00000218  00000-0  10518-4 0  9996
       2 25504  24.9967 319.8664 0017431 121.3810   9.7939 14.44057429 65541
       """;

julia> read_tle_from_string(tles)
2-element Array{TLE,1}:
 TLE: SCD 1 (Epoch = 2018-12-25T18:17:32)
 TLE: SCD 2 (Epoch = 2018-12-26T05:50:03)

julia> tle_l1 = "1 22490U 93009B   18359.76217587  .00000186  00000-0  84512-6 0  9998"
"1 22490U 93009B   18359.76217587  .00000186  00000-0  84512-6 0  9998"

julia> tle_l2 = "2 22490  24.9694 116.1709 0043211  90.3968  62.0083 14.44539396366163"
"2 22490  24.9694 116.1709 0043211  90.3968  62.0083 14.44539396366163"

julia> read_tle_from_string(tle_l1, tle_l2)
1-element Array{TLE,1}:
 TLE: UNDEFINED (Epoch = 2018-12-25T18:17:32)

It is also available two special types of strings, tle" and tlenc", that automatically loads a set of TLEs. In the first case the checksum is verified whereas in the second case it is not.

julia> tles = tle"""
       SCD 1
       1 22490U 93009B   18359.76217587  .00000186  00000-0  84512-6 0  9998
       2 22490  24.9694 116.1709 0043211  90.3968  62.0083 14.44539396366163
       SCD 2
       1 25504U 98060A   18360.24309362  .00000218  00000-0  10518-4 0  9996
       2 25504  24.9967 319.8664 0017431 121.3810   9.7939 14.44057429 65541
       """
2-element Array{TLE,1}:
 TLE: SCD 1 (Epoch = 2018-12-25T18:17:32)
 TLE: SCD 2 (Epoch = 2018-12-26T05:50:03)

julia> tles = tle"""
       SCD 1
       1 22490U 93009B   18359.76217587  .00000186  00000-0  84512-6 0  9998
       2 22490  24.9694 116.1709 0043211  90.3968  62.0083 14.44539396366164
       """
ERROR: LoadError: The TLE file is not valid (error in line 3): Expected checksum: 3, line checksum: 4.
...

julia> tles = tlenc"""
       SCD 1
       1 22490U 93009B   18359.76217587  .00000186  00000-0  84512-6 0  9998
       2 22490  24.9694 116.1709 0043211  90.3968  62.0083 14.44539396366164
       """
1-element Array{TLE,1}:
 TLE: SCD 1 (Epoch = 2018-12-25T18:17:32)