Source code for adam_core.dynamics.tisserand

"""
This code generates the dictionary of semi-major axes for the
third body needed for the Tisserand parameter

from adam_core.orbits.query import _get_horizons_elements

ids = ["199", "299", "399", "499", "599", "699", "799", "899"]
elements = _get_horizons_elements(ids, times, id_type="majorbody")

MAJOR_BODIES = {}
for i, r in elements[["targetname", "a"]].iterrows():
   body_name = r["targetname"].split(" ")[0].lower()
   MAJOR_BODIES[body_name] = r["a"]

"""

import numpy as np

MAJOR_BODIES = {
    "mercury": 0.3870970330236769,
    "venus": 0.723341974974844,
    "earth": 0.9997889954736553,
    "mars": 1.523803685638066,
    "jupiter": 5.203719697535582,
    "saturn": 9.579110220472034,
    "uranus": 19.18646168457971,
    "neptune": 30.22486701698071,
}




def calc_tisserand_parameter(a, e, i, third_body="jupiter"):
    """
    Calculate Tisserand's parameter used to identify potential comets.
    For example, objects with Tisserand parameter's with respect to Jupiter greater than 3 are
    typically asteroids, whereas Jupiter family comets may have Tisserand's parameter
    between 2 and 3. Damocloids have Jupiter Tisserand's parameter of less than 2.

    Parameters
    ----------
    a : float or `~numpy.ndarray` (N)
        Semi-major axis in au.
    e : float or `~numpy.ndarray` (N)
        Eccentricity.
    i : float or `~numpy.ndarray` (N)
        Inclination in degrees.
    third_body : str
        Name of planet with respect to which Tisserand's parameter
        should be calculated.

    Returns
    -------
    Tp : float or `~numpy.ndarray` (N)
        Tisserand's parameter.
    """
    i_rad = np.radians(i)

    major_bodies = MAJOR_BODIES.keys()
    if third_body not in major_bodies:
        err = f"third_body should be one of {','.join(major_bodies)}"
        raise ValueError(err)

    ap = MAJOR_BODIES[third_body]
    Tp = ap / a + 2 * np.cos(i_rad) * np.sqrt(a / ap * (1 - e**2))

    return Tp