def test_is_sun_sync_returns_true_for_sun_sync_orbit():
pred1 = J2Predictor.sun_synchronous(alt_km=500, ecc=0)
pred2 = J2Predictor.sun_synchronous(alt_km=500, inc_deg=97)
pred3 = J2Predictor.sun_synchronous(ecc=0, inc_deg=97)
assert is_sun_synchronous(pred1)
assert is_sun_synchronous(pred2)
assert is_sun_synchronous(pred3)
def test_sun_sync_from_eccentricity_and_inclination(self):
# Vallado 3rd edition, example 11-2
expected_sma = 7346.846
pred = J2Predictor.sun_synchronous(ecc=0.2, inc_deg=98.6)
self.assertAlmostEqual(pred.get_position().osculating_elements[0],
expected_sma,
places=1)
def test_sun_sync_from_altitude_and_inclination(self):
# Hardcoded from our implementation
expected_ecc = 0.14546153131334466
pred = J2Predictor.sun_synchronous(alt_km=475, inc_deg=97)
self.assertAlmostEqual(pred.get_position().osculating_elements[1],
expected_ecc,
places=14)
def test_sun_sync_from_altitude_and_eccentricity(self):
# Vallado 3rd edition, example 11-2
expected_inc = 98.6
pred = J2Predictor.sun_synchronous(alt_km=800, ecc=0)
self.assertAlmostEqual(pred.get_position().osculating_elements[2],
expected_inc,
places=2)
def test_sun_sync_delta_true_anomaly_non_circular(self):
date = dt.datetime.today().date()
ltan_h = 12
expected_ref_epoch = dt.datetime(date.year, date.month, date.day, 12)
for expected_ta_deg in [-30, 30]:
pred = J2Predictor.sun_synchronous(
alt_km=475, ecc=0.1455, date=date, ltan_h=ltan_h, ta_deg=expected_ta_deg
)
ta_deg = pred.get_position(expected_ref_epoch).osculating_elements[5]
self.assertAlmostEqual(ta_deg, expected_ta_deg % 360, places=12)
def test_sun_sync_delta_true_anomaly_non_circular(self):
date = dt.datetime.today().date()
ltan_h = 12
expected_ref_epoch = dt.datetime(date.year, date.month, date.day, 12)
for ta_deg in [-30, 30]:
pred = J2Predictor.sun_synchronous(
alt_km=475, ecc=0.1455, date=date, ltan_h=ltan_h, ta_deg=ta_deg
)
self.assertEqual(pred._ta, ta_deg)
self.assertEqual(pred._epoch, expected_ref_epoch)
def test_eclipse_corner_case():
# See https://github.com/satellogic/orbit-predictor/issues/96
start = dt.datetime(2020, 9, 1)
end = dt.datetime(2020, 9, 2)
pred = J2Predictor.sun_synchronous(
alt_km=470.0,
ecc=0.001,
ltan_h=19,
ta_deg=0,
date=start,
)
eclipses = list(pred.eclipses_since(when_utc=start, limit_date=end))
assert len(eclipses) == 16