Remote Sensor

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Description

The Remote Sensor is a base class for sensors that observe the external environment using a field of view. Unlike internal sensors that measure on-board state, remote sensors detect external targets such as celestial bodies, terrain, or other spacecraft. This class extends the base Sensor and provides common functionality for field of view modeling, boresight alignment, and integration with the Planet Coverage System for coverage analysis.

Derived sensor types include cameras, star trackers, sun sensors, Earth horizon sensors, RADAR, and laser range finders.

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Module Implementation

Field of View

The sensor’s field of view defines the angular extent of the observable region, specified in degrees along the sensor’s boresight (Up) axis. Targets outside this cone are not detected.

Boresight and Alignment Error

The sensor boresight is the primary viewing direction, nominally aligned with the sensor’s Up axis in the local frame. An alignment error can be applied to model boresight misalignment, implemented as a pitch rotation about the local Right axis:

$${\mathbf{R}}_{\text{eff}}={\mathbf{R}}_{\text{sensor}}\cdot {\mathbf{R}}_{\text{pitch}}({\theta }_{\text{align}})$$

where ${\theta }_{\text{align}}$ is the alignment error in degrees. The effective boresight direction in the inertial frame is the Up vector of this combined rotation.

Planet Coverage Tracking

Remote sensors can register with the Planet Coverage System to track cumulative observation coverage over a celestial body. When registered, the system maintains a grid of accumulated dwell time for each latitude-longitude cell observed by the sensor.

Coverage metrics include:

• Dwell Time: Accumulated observation time at each grid cell
• Resolution: Best (minimum) ground resolution achieved at each cell
• Total Coverage: Fraction of grid cells observed at least once

Areas of Interest

Sensors can define areas of interest (AOIs) with finer grid resolution for detailed coverage analysis over specific regions. Each AOI specifies latitude and longitude bounds with configurable grid density, enabling high-resolution tracking within the region while maintaining coarser global coverage.

Ground Object Detection

The sensor provides methods to determine whether a ground object’s location was observed and whether the observation resolution was sufficient to detect objects of a given size. An object is detectable when:

1. The object’s location was observed at least once
2. The sensor’s resolution at that location is less than or equal to the object size

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Assumptions/Limitations

• This is an abstract base class; it cannot be instantiated directly.
• Field of view is modeled as a circular cone; derived sensors may override this with specific aperture geometries.
• Alignment error is limited to pitch-axis misalignment; roll and yaw errors require additional error models.
• Coverage tracking requires explicit registration with the Planet Coverage System.