Ground Access Control Software

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Description

This flight software component monitors and controls ground station access for a spacecraft. It automatically tracks all ground stations that the spacecraft can communicate with and outputs a device status message indicating whether the spacecraft currently has access to any ground station.

On initialization, the software automatically discovers all Ground Stations on the same planet as the spacecraft’s orbited body and subscribes to their access messages. During simulation, it continuously evaluates these access messages to determine if the spacecraft is within communication range of any ground station.

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Example Use Cases

• Communication Window Detection: Automatically detect when a spacecraft enters or exits communication range with ground stations for scheduling data downlinks.
• Ground Contact Triggering: Use the output device status to trigger other systems or software when ground contact is established.
• Multi-Station Coverage Analysis: Monitor access to multiple ground stations simultaneously to analyze ground network coverage.
• Autonomous Operations: Enable autonomous spacecraft behaviors that depend on ground station visibility, such as switching between autonomous and ground-controlled modes.

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Module Implementation

Initialization

During the simulation begin phase, the software:

1. Finds the parent Spacecraft in the object hierarchy
2. Discovers all Ground Stations in the simulation
3. Filters ground stations to only those on the same planet as the spacecraft’s orbited body
4. Subscribes to the access message from each relevant ground station by calling TrackObject on the spacecraft

Access Evaluation

Each simulation update, the software evaluates all subscribed access messages:

$$\text{HasAccess}=\underset{i=1}{\overset{n}{\bigvee }}{\text{IsAccessible}}_i$$

where $n$ is the number of tracked ground stations and ${\text{IsAccessible}}_i$ indicates whether the $i$-th ground station has line-of-sight access to the spacecraft.

The result is a logical OR operation—if any ground station reports access, the output device status is set to active.

Output

The software produces a device status message with the IsActive flag set based on the access evaluation:

• IsActive = true: The spacecraft has access to at least one ground station
• IsActive = false: The spacecraft has no access to any ground station

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Assumptions/Limitations

• The software only considers ground stations on the same planet as the spacecraft’s orbited body. Ground stations on other celestial bodies are ignored.
• Access messages must be provided by the ground stations via their TrackObject method.
• If additional access messages need to be tracked beyond the automatic discovery, they can be added manually using the AddAccessMessage method.