Optical Transmitter Alignment Error Model

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Description

The Optical Transmitter Alignment Error Model introduces configurable pointing errors to an Optical Transmitter component. This model simulates misalignment of the laser emitter due to mechanical tolerances, thermal distortion, or vibration-induced jitter. By adjusting the alignment error, users can evaluate the impact of pointing accuracy on optical link performance and margin.

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Example Use Cases

• Pointing Error Analysis: Assess link degradation due to spacecraft attitude determination and control system errors.
• Mechanical Tolerance Studies: Evaluate the impact of manufacturing tolerances on optical terminal alignment.
• Thermal Distortion Effects: Model beam wander caused by thermal gradients across the optical assembly.
• Sensitivity Analysis: Determine alignment requirements for a given link margin budget.

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Module Implementation

The alignment error model is attached to an Optical Transmitter and applies a rotational offset to the emitter beam axis.

Alignment Error Application

The model applies a single-axis rotational error to the transmitter’s beam direction. The alignment error $ϵ$ [deg] rotates the beam about the pitch axis:

$${\hat{\mathbf{b}}}_{\text{actual}}={\mathbf{R}}_{\text{error}}(ϵ)\cdot {\hat{\mathbf{b}}}_{\text{nominal}}$$

where ${\mathbf{R}}_{\text{error}}$ is a rotation matrix about the emitter’s right axis.

Effect on Link Geometry

The alignment error increases the effective off-axis angle to the receiver. For a receiver nominally aligned with the beam axis, the resulting pointing error causes the receiver to appear at an angle $\theta$ from the actual beam center:

$${\theta }_{\text{eff}}={\theta }_{\text{nominal}}+ϵ$$

This increased off-axis angle affects link validity and bit rate scaling as computed by the Optical Transmitter.

Dynamic Adjustment

The alignment error can be modified during simulation, allowing users to:

• Simulate time-varying disturbances (e.g., reaction wheel jitter)
• Model gradual thermal drift during orbit transitions
• Inject step changes for fault analysis

The updated alignment error is applied to the parent transmitter each simulation step.

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Assumptions/Limitations

• The alignment error is applied about a single axis (pitch); multi-axis errors require additional modelling.
• The error is deterministic; stochastic jitter models must be implemented externally by varying the parameter.
• The model does not account for the physical source of misalignment (thermal, mechanical, vibration).
• Detaching the model does not reset the parent transmitter’s alignment error