Quick Start

Let's suppose we want to discover the ISS position on May 19, 2013, at 12:00:00. First, we need to obtain a description of its orbit and use the corresponding propagator. Using the Celestrak service, for example, we can obtain the ISS TLE on May 18, 2023:

ISS (ZARYA)             
1 25544U 98067A   23138.86946505 -.00404279  00000+0 -74572-2 0  9994
2 25544  51.6431 113.8899 0006661 357.1286  88.0982 15.49924990397244

Since we have a TLE, we must use the SGP4/SDP4 propagator. Let's initialize the algorithm first:

julia> iss_tle = tle"""
           ISS (ZARYA)
           1 25544U 98067A   23138.86946505 -.00404279  00000+0 -74572-2 0  9994
           2 25544  51.6431 113.8899 0006661 357.1286  88.0982 15.49924990397244"""TLE:
                      Name : ISS (ZARYA)
          Satellite number : 25544
  International designator : 98067A
        Epoch (Year / Day) : 23 / 138.86946505 (2023-05-18T20:52:01.780)
        Element set number : 999
              Eccentricity :   0.00066610
               Inclination :  51.64310000 deg
                      RAAN : 113.88990000 deg
       Argument of perigee : 357.12860000 deg
              Mean anomaly :  88.09820000 deg
           Mean motion (n) :  15.49924990 revs / day
         Revolution number : 39724
                        B* :   -0.0074572 1 / er
                     ṅ / 2 :  -0.00404279 rev / day²
                     n̈ / 6 :            0 rev / day³
julia> orbp = Propagators.init(Val(:SGP4), iss_tle)OrbitPropagatorSgp4{Float64, Float64}:
   Propagator name : SGP4 Orbit Propagator
  Propagator epoch : 2023-05-18T20:52:01.780
  Last propagation : 2023-05-18T20:52:01.780

Now we can propagate the ISS orbit to the desired epoch and obtain its state vector and mean elements:

julia> Propagators.propagate_to_epoch!(orbp, date_to_jd(2023, 5, 19, 12, 0, 0))([-2.7473591812349055e6, 6.194023092402147e6, 470636.34213714604], [-4186.242303388817, -2319.0180933770293, 5989.510493513584])
julia> Propagators.mean_elements(orbp)KeplerianElements{Float64, Float64}:
           Epoch :    2.46008e6 (2023-05-19T12:00:00)
 Semi-major axis : 6796.64        km
    Eccentricity :    0.000670975
     Inclination :   51.6431      °
            RAAN :  110.767       °
 Arg. of Perigee :  359.796       °
    True Anomaly :    5.37263     °