def gen_trajectory(self, tle, interval):
"""
Generates the trajectory (time and coordinate information) for the given
interval with the internal stepsize.
Parameters
----------
tle : TLE
Two-Line-Element initial orbit information (TEME mean orbital elements)
interval : TimeInterval
Time interval for which the ephemeris will be generated
Returns
-------
Trajectory
The output trajectory (in `GCRS`)
"""
# generate number of steps (forced to rounded up int)
no_of_steps = np.ceil((interval.duration / self.stepsize).decompose())
# make sure there are enough elements for interpolation
if no_of_steps < Trajectory.reqd_min_elements():
no_of_steps = Trajectory.reqd_min_elements()
# time list
time_list = interval.start + self.stepsize * np.arange(0, no_of_steps)
time_list.format = "isot"
# ****** Generate the pos, vel vectors for each time instant ******
# Run the propagation and init pos and vel vectors in TEME
e, r_list, v_list = tle.satrec.sgp4_array(time_list.jd1, time_list.jd2)
# Load the time, pos, vel info into astropy objects (shallow copied)
rv_list_teme = CartesianRepresentation(
r_list, unit=u.km, xyz_axis=1).with_differentials(
CartesianDifferential(v_list, unit=u.km / u.s, xyz_axis=1))
rv_list_gcrs = TEME(
rv_list_teme,
obstime=time_list,
representation_type="cartesian",
differential_type="cartesian",
).transform_to(GCRS(obstime=time_list))
# trajectory in astropy
traj_astropy = SkyCoord(
rv_list_gcrs,
obstime=time_list,
frame="gcrs",
representation_type="cartesian",
differential_type="cartesian",
)
# Init trajectory in Trajectory object
trajectory = Trajectory(traj_astropy)
return trajectory
def gen_trajectory(self, tle, interval):
"""
Generates the trajectory (time and coordinate information) for the given
interval with the internal stepsize.
Parameters
----------
tle : TLE
Two-Line-Element initial orbit information (TEME mean orbital elements)
interval : TimeInterval
Time interval for which the ephemeris will be generated
Returns
-------
Trajectory
The output trajectory (in `GCRS`)
"""
# ****** Generate the pos, vel vectors for each time instant ******
# generate the output timelist
time_list = self._generate_time_list(interval)
# Run the propagation and init pos and vel vectors in TEME
e, r_list, v_list = tle.satrec.sgp4_array(time_list.jd1, time_list.jd2)
# Load the time, pos, vel info into astropy objects (shallow copied)
rv_list_teme = CartesianRepresentation(
r_list, unit=u.km, xyz_axis=1
).with_differentials(CartesianDifferential(v_list, unit=u.km / u.s, xyz_axis=1))
rv_list_gcrs = TEME(
rv_list_teme,
obstime=time_list,
representation_type="cartesian",
differential_type="cartesian",
).transform_to(GCRS(obstime=time_list))
# trajectory in astropy
traj_astropy = SkyCoord(
rv_list_gcrs,
obstime=time_list,
frame="gcrs",
representation_type="cartesian",
differential_type="cartesian",
)
# Init trajectory in Trajectory object
trajectory = Trajectory(traj_astropy)
return trajectory
def test_itrs_to_teme():
"""Check the coordinate transform accuracy."""
# test_frame = "TEME"
allowable_pos_diff = 300 * u.mm
allowable_vel_diff = 0.21 * u.mm / u.s
rv_teme = rv_itrs_true.transform_to(TEME(obstime=time))
r_diff = pos_err(rv_teme, rv_teme_true)
v_diff = vel_err(rv_teme, rv_teme_true)
# print(f"r {test_frame} diff : {r_diff}")
# print(f"v {test_frame} diff : {v_diff}")
assert approx(r_diff.value, abs=allowable_pos_diff.value) == 0.0
assert approx(v_diff.value, abs=allowable_vel_diff.value) == 0.0
def test_itrs_roundtrip():
"""Check whether transforming to a coord and then
transforming back yields the same output."""
# test_frame = "ITRS"
allowable_pos_diff = 1.5e-6 * u.mm
allowable_vel_diff = 2.2e-9 * u.mm / u.s
rv_teme = rv_itrs_true.transform_to(TEME(obstime=time))
rv_itrs_from_teme = rv_teme.transform_to(ITRS(obstime=time))
r_diff = pos_err(rv_itrs_from_teme, rv_itrs_true)
v_diff = vel_err(rv_itrs_from_teme, rv_itrs_true)
# print(f"r {test_frame} diff : {r_diff}")
# print(f"v {test_frame} diff : {v_diff}")
assert approx(r_diff.value, abs=allowable_pos_diff.value) == 0.0
assert approx(v_diff.value, abs=allowable_vel_diff.value) == 0.0
def propagate(tle, time):
"""
Computes the coordinates at the target `time` using the source `TLE` mean
orbital elements.
Parameters
----------
tle : TLE
Mean orbital elements (Two-Line-Element)
time : Time
Target time for propagation
Returns
-------
coords : SkyCoord
Coordinates at target time (in `GCRS`)
Raises
------
SGP4GeneralError
Errors in SGP4 propagation
SGP4SatDecayedError
Satellite coordinates at required coordinates are below decay altitude.
"""
# compute coords at time
e, r, v = tle.satrec.sgp4(time.utc.jd1, time.utc.jd2)
# check error code
SGP4Propagator.__handle_err_code(e)
v_teme = CartesianDifferential(np.asarray(v), unit=u.km / u.s)
r_teme = CartesianRepresentation(np.asarray(r), unit=u.km)
rv_gcrs = TEME(r_teme.with_differentials(v_teme),
obstime=time).transform_to(GCRS(obstime=time))
return SkyCoord(
rv_gcrs,
representation_type="cartesian",
differential_type="cartesian",
)
def test_teme_to_tirs_no_vel():
"""Check whether coord transform without velocity is possible."""
rv_teme_no_vel = TEME(r_teme_true,
obstime=time,
representation_type="cartesian")
rv_teme_no_vel.transform_to(TIRS(obstime=time))
[-1033.47503120, 7901.30558560, 6380.34453270], unit=u.km)
rv_tirs_true = TIRS(
r_tirs_true.with_differentials(v_tirs_true),
obstime=time,
representation_type="cartesian",
differential_type="cartesian",
)
# Vallado IAU 2000 - Table 3-6 TEME
v_teme_true = CartesianDifferential(
[-4.7461314870, 0.7858180410, 5.5319312880], unit=u.km / u.s)
r_teme_true = CartesianRepresentation(
[5094.18016210, 6127.64465950, 6380.34453270], unit=u.km)
rv_teme_true = TEME(
r_teme_true.with_differentials(v_teme_true),
obstime=time,
representation_type="cartesian",
differential_type="cartesian",
)
def pos_err(rv_test, rv_true):
"""
Computes positional error between two vectors defined in a frame.
Parameters
----------
rv_test : State with position vector under test
rv_true : State with true position vector
Returns
-------