def test_from_coord_fails_if_no_time_differential():
pos = [30000, 0, 0] * u.km
cartrep = CartesianRepresentation(*pos)
# Method fails if coordinate instance doesn't contain a differential with respect to time
with pytest.raises(ValueError) as excinfo:
Orbit.from_coords(Earth, SkyCoord(cartrep))
assert (
"ValueError: Coordinate instance doesn't have a differential with respect to time"
in excinfo.exconly())
def test_from_coord_fails_for_multiple_positions(obstime):
cartdiff = CartesianDifferential([[0, 1, 0], [-0.1, 0.9, 0]] * u.km / u.s,
xyz_axis=1)
cartrep = CartesianRepresentation([[1, 0, 0], [0.9, 0.1, 0]] * u.km,
differentials=cartdiff,
xyz_axis=1)
coords = GCRS(cartrep,
representation_type=CartesianRepresentation,
obstime=obstime)
with pytest.raises(ValueError) as excinfo:
Orbit.from_coords(Earth, coords)
assert (
"ValueError: Coordinate instance must represents exactly 1 position, found: 2"
in excinfo.exconly())
def test_orbit_creation_using_frame_obj(attractor, frame, obstime):
vel = [0, 2, 0] * u.km / u.s
cartdiff = CartesianDifferential(*vel)
pos = [30000, 0, 0] * u.km
cartrep = CartesianRepresentation(*pos, differentials=cartdiff)
coord = frame(cartrep, obstime=obstime)
o = Orbit.from_coords(attractor, coord)
inertial_frame_at_body_centre = get_frame(attractor,
Planes.EARTH_EQUATOR,
obstime=coord.obstime)
coord_transformed_to_irf = coord.transform_to(
inertial_frame_at_body_centre)
pos_transformed_to_irf = coord_transformed_to_irf.cartesian.xyz
vel_transformed_to_irf = coord_transformed_to_irf.cartesian.differentials[
"s"].d_xyz
assert_quantity_allclose(o.r, pos_transformed_to_irf, atol=1e-5 * u.km)
assert_quantity_allclose(o.v,
vel_transformed_to_irf,
atol=1e-5 * u.km / u.s)
def test_from_coord_if_coord_is_not_of_shape_zero():
pos = [0, 1, 0]
vel = [1, 0, 0]
cartdiff = CartesianDifferential([vel] * u.km / u.s, xyz_axis=1)
cartrep = CartesianRepresentation([pos] * u.km,
differentials=cartdiff,
xyz_axis=1)
coords = GCRS(cartrep,
representation_type=CartesianRepresentation,
obstime=J2000)
ss = Orbit.from_coords(Earth, coords)
assert_quantity_allclose(ss.r, pos * u.km, rtol=1e-5)
assert_quantity_allclose(ss.v, vel * u.km / u.s, rtol=1e-5)
def test_orbit_creation_using_skycoord(attractor):
vel = [0, 2, 0] * u.km / u.s
cartdiff = CartesianDifferential(*vel)
pos = [30000, 0, 0] * u.km
cartrep = CartesianRepresentation(*pos, differentials=cartdiff)
coord = SkyCoord(cartrep, frame="icrs")
o = Orbit.from_coords(attractor, coord)
inertial_frame_at_body_centre = get_frame(attractor,
Planes.EARTH_EQUATOR,
obstime=coord.obstime)
coord_transformed_to_irf = coord.transform_to(
inertial_frame_at_body_centre)
pos_transformed_to_irf = coord_transformed_to_irf.cartesian.xyz
vel_transformed_to_irf = coord_transformed_to_irf.cartesian.differentials[
"s"].d_xyz
assert (o.r == pos_transformed_to_irf).all()
assert (o.v == vel_transformed_to_irf).all()
def el2rv(inc, raan, ecc, argp, mean_anomaly, mean_motion, epoch):
"""
Converts mean orbital elements to state vector
"""
time_tle = epoch.jd - 2433281.5
sat = Satrec()
sat.sgp4init(
WGS84,
"i",
0,
time_tle,
0.0,
0.0,
0.0,
ecc,
argp,
inc,
mean_anomaly,
mean_motion,
raan,
)
errorCode, rTEME, vTEME = sat.sgp4(epoch.jd1, epoch.jd2)
if errorCode != 0:
raise RuntimeError(SGP4_ERRORS[errorCode])
pTEME = coord.CartesianRepresentation(rTEME * u.km)
vTEME = coord.CartesianDifferential(vTEME * u.km / u.s)
svTEME = TEME(pTEME.with_differentials(vTEME), obstime=epoch)
svITRS = svTEME.transform_to(coord.ITRS(obstime=epoch))
orb = Orbit.from_coords(Earth, svITRS)
return orb.r, orb.v
0.0,
0.0,
ecc,
argp,
inc,
m_ano,
m_mot,
raan,
)
errorCode, rTEME, vTEME = sat.sgp4(epoch.jd1, epoch.jd2)
if errorCode != 0:
raise RuntimeError(SGP4_ERRORS[errorCode])
# Convert state vector from TEME (True Equator Mean Equinox) to ITRS
pTEME = coord.CartesianRepresentation(rTEME * u.km)
vTEME = coord.CartesianDifferential(vTEME * u.km / u.s)
svTEME = TEME(pTEME.with_differentials(vTEME), obstime=iss.epoch)
svITRS = svTEME.transform_to(coord.ITRS(obstime=iss.epoch))
sv = Orbit.from_coords(Earth, svITRS)
# Display results
print("State vector [rv2el]")
print(f" r = {sv.r}")
print(f" v = {sv.v}")
print()
print("State vector differences [poliastro - rv2el]")
print(f" dr = {iss.r - sv.r}")
print(f" dv = {iss.v - sv.v}")
print()
