gcrf_to_lunar_fixed

ssapy.utils.gcrf_to_lunar_fixed(r, t, v=None)[source][source]

Transform position and velocity vectors from the GCRF (Geocentric Celestial Reference Frame) to a Moon-fixed (lunar-centric) frame.

This function adjusts the position and velocity vectors to account for the Moon’s motion, effectively transforming them into a frame fixed to the Moon.

Parameters:

r (numpy array): Position vector(s) in the GCRF [x, y, z]. t (numpy array): Time(s) at which the position vector(s) are defined. v (numpy array, optional): Velocity vector(s) in the GCRF [vx, vy, vz]. If not provided, only position is transformed.

Returns:

numpy array or tuple:

  • If v is not provided: Transformed position vector(s) in the Moon-fixed frame.

  • If v is provided: A tuple containing:

    • r_lunar (numpy array): Transformed position vector(s) in the Moon-fixed frame.

    • v_lunar (numpy array): Transformed velocity vector(s) in the Moon-fixed frame.

Notes:

  • The get_body function is used to retrieve the Moon’s position at a given time.

  • The Moon’s position is subtracted from the transformed lunar-centric position to obtain a Moon-fixed reference frame.

  • If velocity is provided, it is recalculated in the Moon-fixed frame using the v_from_r function.