ADCS.CONOPS.goals.vector_goals.nadir_goal module

class ADCS.CONOPS.goals.vector_goals.nadir_goal.Nadir_Goal(boresight_name=None)

Bases: Vector_Goal

Nadir-pointing vector goal.

This goal commands alignment with the local nadir direction, i.e. the unit vector from the spacecraft toward the Earth’s center, expressed in the inertial (ECI) frame:

\[\hat{\mathbf{r}} = \frac{\mathbf{r}}{\|\mathbf{r}\|}, \qquad \mathbf{r}_{goal} = -\hat{\mathbf{r}}.\]

A feed-forward reference angular velocity is provided to track the rotating nadir direction in inertial space:

\[\boldsymbol{\omega}_{ref} = \frac{\mathbf{r}\times\mathbf{v}}{\|\mathbf{r}\|^2}.\]

Here \(\mathbf{r}\) and \(\mathbf{v}\) are the spacecraft ECI position and velocity.

Parameters:

boresight_name (str | None)

to_ref(os0)

Generate a reference inertial direction and angular velocity.

Subclasses must implement this method to compute a desired inertial reference vector

\[\mathbf{v}_{\mathrm{ref}} \in \mathbb{R}^3\]

based on the current orbital state. The returned vector is expected to be nonzero and will typically be normalized by the downstream error computation.

Parameters:

os0 (Orbital_State) – Current orbital state.

Returns:

Reference inertial direction and reference angular velocity.

Return type:

Tuple[numpy.ndarray, numpy.ndarray]