Transmitter Storage Model

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Description

The Transmitter Storage Model enables automated transmission of stored data from a partitioned storage system. This model attaches to a Transmitter component and monitors communication access windows, automatically pulling buffered messages from storage and transmitting them when a link is available. This functionality is essential for store-and-forward communication architectures where spacecraft collect data continuously but can only downlink during periodic ground station passes.

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Example Use Cases

• Telemetry Downlink: Automatically transmit buffered telemetry data during ground station contact windows.
• Science Data Transfer: Download stored payload data when communication access is established.
• Store-and-Forward Relay: Retransmit previously received messages when the next communication opportunity arises.

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Module Implementation

The Transmitter Storage Model is a Universe Model that attaches to a Transmitter component and manages the flow of stored messages to the transmission queue.

Access Gating

The model monitors the communication link status to determine when transmission is permitted:

$$\text{transmit}=\{\begin{array}{ll}\text{true}& \text{if ForceTransmit}=\text{true}\\ \text{true}& \text{if AccessMsg}\ne \text{null}\wedge \text{IsAccessible}=\text{true}\\ \text{false}& \text{otherwise}\end{array}$$

The ForceTransmit flag bypasses access checking, which is useful for testing or scenarios where access is managed externally.

Message Retrieval

When transmission is permitted, the model continuously retrieves messages from the storage buffer until no more data remains:

1. Pop the next message from the Data Storage Message Writer buffer
2. Extract message metadata (name and identifier)
3. Generate a transmission key from the metadata
4. Queue the message for transmission via the parent transmitter

Key Generation

Each transmitted message is assigned a unique key derived from its metadata:

$$k=\text{"m\_"}+\text{name}+\text{"\_"}+\text{id}$$

This key enables the receiving system to identify and categorize incoming messages.

Buffer Draining

The model attempts to drain the entire transmission buffer during each access window. The transmission loop continues until:

• The storage buffer is empty, or
• The access window ends (checked on subsequent updates)

This approach maximizes data return during limited contact opportunities.

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Assumptions/Limitations

• The model requires a valid Data Storage Message Writer reference to function.
• Messages are transmitted in the order they were stored (FIFO).
• The model does not check transmitter capacity or data rate limits; it queues all available messages.
• Transmission timing within an access window is not modeled; all queued messages are assumed to be transmitted.
• The ForceTransmit flag bypasses all access validation, which may not be physically realistic.
• Message metadata is removed before transmission to