pymgp.satorb.vec2orb#

pymgp.satorb.vec2orb(svec, GM=398600441800000.0)[source]#

Convert inertial state vector into Keplerian elements.

This function converts an array with 6-element inertial state vector(s), with cartesian position and velocity [X, Y, Z, Xdot, Ydot, Zdot], into an array with the 6 Keplerian elements.

Parameters:
svecarray_like with shape (…,6)

Array with 6-element inertial state vector svec with Cartesian position and velocity [X, Y, Z, Xdot, Ydot, Zdot] in an ECI frame. Units are meter and meter/sec

GMfloat, optional

Value of GM. Default for GM [meter**3/sec**2] is the IERS 1996 standard value for the Earth (GM=3986004418e5)

Returns:
orbndarray with shape (…,6) similar to svec

Array with the 6 Keplerian elements [ Semi-major axis (meters), Eccentricity (unity), Inclination (radians), Right ascension of the ascending node (radians), Argument of the pericenter (radians), True anomaly (radians) ]. Units are meters or radians.

See also

orb2vec, kepler, keplernu, keplerm

Notes

The computations do not do special hanling of circular or equatorial orbits. This is possible because atan2(0,0)=0 is defined in numpy, however, some pairs of angles will actually be singular.

Examples

>>> vec2orb([-5767701.7786, -3097382.0132, 2737195.4374,  3001.4240, -6762.1059, -1280.2560])
array([7.12138217e+06, 4.31759805e-03, 4.35789999e-01, 1.60777001e+00,
       1.39024880e+00, 5.98791190e-01])

>>> #              X              Y             Z            Vx          Vy          Vz
>>> svec = [[-5767701.7786, -3097382.0132, 2737195.4374,  3001.4240, -6762.1059, -1280.2560],
...         [ -625224.3608, -7162713.9833,   16233.9739, -1131.8951,   116.3879,  7358.7436],
...         [-2301220.9378,  6666917.3737,  968353.5303, -6610.7556, -1833.8971, -2992.6557]]
>>> vec2orb(svec)
array([[7.12138217e+06, 4.31759805e-03, 4.35789999e-01, 1.60777001e+00,
        1.39024880e+00, 5.98791190e-01],
       [7.19093100e+06, 1.80794915e-04, 1.72419000e+00, 4.62567000e+00,
        7.39124272e-01, 5.54634573e+00],
       [7.12297382e+06, 1.74770022e-03, 4.36259992e-01, 5.34368001e+00,
        1.56062623e+00, 1.25322376e+00]])
>>> vec2orb(svec).shape
(3, 6)

>>> vec2orb([svec, svec]).shape
(2, 3, 6)
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