def test_convert_coe_to_rv(self):
# Data from Vallado, example 2.6
p = 11067.790
ecc = 0.83285
inc = radians(87.87)
raan = radians(227.89)
argp = radians(53.38)
ta = radians(92.335)
expected_position = [6525.344, 6861.535, 6449.125]
expected_velocity = [4.902276, 5.533124, -1.975709]
position, velocity = coe2rv(MU_E, p, ecc, inc, raan, argp, ta)
assert_allclose(position, expected_position, rtol=1e-5)
assert_allclose(velocity, expected_velocity, rtol=1e-5)
def kepler(argp, delta_t_sec, ecc, inc, p, raan, sma, ta):
# Initial mean anomaly
M_0 = ta_to_M(ta, ecc)
# Mean motion
n = sqrt(wgs84.mu / sma**3)
# Propagation
M = M_0 + n * delta_t_sec
# New true anomaly
ta = M_to_ta(M, ecc)
# Position and velocity vectors
position_eci, velocity_eci = coe2rv(MU_E, p, ecc, inc, raan, argp, ta)
return position_eci, velocity_eci
def pkepler(argp, delta_t_sec, ecc, inc, p, raan, sma, ta):
"""Perturbed Kepler problem (only J2)
Notes
-----
Based on algorithm 64 of Vallado 3rd edition
"""
# Mean motion
n = sqrt(MU_E / sma**3)
# Initial mean anomaly
M_0 = ta_to_M(ta, ecc)
# Update for perturbations
delta_raan = (-(3 * n * R_E_KM**2 * J2) / (2 * p**2) * cos(inc) *
delta_t_sec)
raan = raan + delta_raan
delta_argp = ((3 * n * R_E_KM**2 * J2) / (4 * p**2) *
(4 - 5 * sin(inc)**2) * delta_t_sec)
argp = argp + delta_argp
M0_dot = ((3 * n * R_E_KM**2 * J2) / (4 * p**2) * (2 - 3 * sin(inc)**2) *
sqrt(1 - ecc**2))
M_dot = n + M0_dot
# Propagation
M = M_0 + M_dot * delta_t_sec
# New true anomaly
ta = M_to_ta(M, ecc)
# Position and velocity vectors
position_eci, velocity_eci = coe2rv(MU_E, p, ecc, inc, raan, argp, ta)
return position_eci, velocity_eci
