# ADR 002: Infrared as the Bench Transport

- HTML version: https://robbiepalmer.me/projects/autonomic-satellite-swarm/adrs/002-infrared-bench-transport
- Project: Autonomic Satellite Swarm (https://robbiepalmer.me/projects/autonomic-satellite-swarm.md)
- Status: Accepted
- Date: 2016-07-01

# Context

The three agents need to discover mission requests, return scores, acknowledge messages, and relay
an assignment. A spacecraft radio is outside the prototype's budget and would add licensing,
hardware, and protocol work unrelated to the coordination experiment.

Wired serial, I2C, or SPI would make the bench reliable, but a shared cable would poorly represent
independent vehicles exchanging broadcasts. Cheap infrared transmitters and receivers are readily
available for the Uno, and the Arduino ecosystem already provides an IRremote library.

# Decision

Use infrared for communication among the three boards. Encode mission coordinates, message types,
agent IDs, and scores into compact values carried by IRremote frames.

Treat infrared as a visible, lossy stand-in for a shared radio channel. Do not present it as a
candidate spacecraft link.

# Consequences

The demonstration remains inexpensive and wireless. Line of sight, dropped frames, and the need for
acknowledgements also make communication failures observable on a desk.

Infrared range, framing, collision behavior, and timing say nothing about a flight radio. The wire
encoding is constrained by the chosen library and the Uno's native integer types, so both will need
review before another transport can use the protocol.

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