ADCS.satellite_hardware.disturbances.prop_disturbance module

class ADCS.satellite_hardware.disturbances.prop_disturbance.Prop_Disturbance(torque_nominal, noise=None, estimate_dist=False)

Bases: Disturbance

Propulsion-Induced Disturbance Torque Model

This class models propulsion-related disturbance torques acting on a spacecraft. Such torques typically arise from imperfect thrust alignment, residual thrust during coast phases, asymmetric propellant flow, or unmodeled reaction forces during maneuver execution.

The propulsion disturbance is modeled as a constant nominal torque with an optional additive stochastic noise component. Unlike environmental disturbances (e.g., gravity-gradient or aerodynamic drag), this torque does not depend on the spacecraft attitude or orbital state.

Mathematical Model

The propulsion disturbance torque is expressed as:

\[\mathbf{T}_{\mathrm{prop}}(t) = \mathbf{T}_0 + \mathbf{n}(t),\]

where:

Symbol	Description
\(\mathbf{T}_0\) | Nominal constant propulsion torque [N·m]
\(\mathbf{n}(t)\) | Zero-mean stochastic noise torque [N·m]

The noise term \(\mathbf{n}(t)\) is generated by a user-supplied noise model of type Noise.

Attitude Independence

Since \(\mathbf{T}_{\mathrm{prop}}\) does not depend on the attitude quaternion \(\mathbf{q}\), all attitude derivatives vanish:

\[\frac{\partial \mathbf{T}_{\mathrm{prop}}}{\partial \mathbf{q}} = \mathbf{0}_{3\times4}, \qquad \frac{\partial^2 \mathbf{T}_{\mathrm{prop}}}{\partial \mathbf{q}^2} = \mathbf{0}_{3\times4\times4}.\]

This makes the propulsion disturbance especially simple to include in linearized or second-order attitude dynamics formulations.

Parameters:

• torque_nominal (numpy.ndarray) – Nominal constant propulsion disturbance torque vector.

• noise (Noise) – Noise model providing stochastic torque perturbations.

• estimate_dist (bool)

torque(x, os)

Return the current propulsion disturbance torque.

This method simply returns the internally stored disturbance torque that was most recently updated by update().

The torque is independent of:

• the attitude quaternion in x

• the orbital state os

These parameters are accepted only to maintain interface consistency with other disturbance models derived from Disturbance.

Parameters:

• x (numpy.ndarray) – Full spacecraft state (unused).

• os (Orbital_State) – Orbital state provider (unused).

Returns:

Current propulsion disturbance torque [N·m], shape (3,).

Return type:

numpy.ndarray

torque_qjac()

Compute the Jacobian of the propulsion disturbance torque with respect to the attitude quaternion.

Because the propulsion disturbance torque is constant and does not depend on the attitude quaternion \(\mathbf{q}\), the Jacobian is identically zero:

\[\frac{\partial \mathbf{T}_{\mathrm{prop}}}{\partial \mathbf{q}} = \mathbf{0}_{3\times4}.\]

Returns:

Quaternion Jacobian matrix of zeros, shape (3, 4).

Return type:

numpy.ndarray

torque_qqHess()

Compute the Hessian of the propulsion disturbance torque with respect to the attitude quaternion.

Since \(\mathbf{T}_{\mathrm{prop}}\) is constant, all second-order derivatives vanish:

\[\frac{\partial^2 \mathbf{T}_{\mathrm{prop}}}{\partial \mathbf{q}^2} = \mathbf{0}_{3\times4\times4}.\]

Returns:

Quaternion Hessian tensor of zeros, shape (3, 4, 4).

Return type:

numpy.ndarray

update()

Update the current propulsion disturbance torque.

This method draws a new noise realization from the noise model and updates the current disturbance torque according to:

\[\mathbf{T}_{\mathrm{prop}}(t) = \mathbf{T}_0 + \mathbf{n}(t),\]

where \(\mathbf{n}(t)\) is provided by get_noise().

This method should typically be called once per simulation or control update step.

Returns:

None

Return type:

None