astroforge.force_models.F_mp_srp

astroforge.force_models.F_mp_srp(time, xxdot)

A built-in, medium-fidelity force model for propagating an orbital state. This model includes:

• 8 x 8 spherical harmonic Earth gravity model

• Third body gravitational perturbation from the Sun

• Third body gravitational perturbation from the Moon

• Solar radiation pressure (SRP) model

This model uses a 9-element state vector. The first six are the typical position and velocity vectors. The final three elements are time-constant coefficients of the SRP model: \(\alpha_i\).

The SRP model is:

\[a_{SRP} = \alpha_1 n_1 + \alpha_2 n_2 + \alpha_3 n_3\]

where

• \(n_1\) is in the direction away from the Sun

• \(n_2\) is along the direction of the satellite’s velocity vector

• \(n_3\) is along the direction of the satellite’s position vector.

Parameters:

• time (float) – Time at which the force model is to be evaluated, expressed as a Modified Julian Date (MJD) in the UT1 time system.

• xxdot (NDArray[np.float64]) –

  State vector; should have shape (9, ). The total state vector is:

  \[\begin{split}X = \begin{bmatrix} x \\ v \\ \alpha \end{bmatrix}\end{split}\]

Returns:

ydot – Derivative of the state vector

Return type:

NDArray[np.float64]