Mission Instrumentation

MB4 — Comms Relay Satellite (Level 4: Coordination & Optimisation)

Mission Goal

Build a relay node that receives payload data from one device and forwards it reliably to a base station, with a plan for message loss, collisions, and verification.

Why This Matters

Real missions often use relays (or constellations) to move data from sensors to ground. Level 4 is about making your design work with other teams and improving reliability under constraints.

What Data You Collect

• Inbound payload messages (from a “satellite” device)
• Relay metadata: relay ID, hop count, receive signal quality proxy (if available)
• Delivery confirmation counts (ACKs received vs sent)

Hardware / Software Needed

• 3 × micro:bit (sender payload, relay, base station receiver)
• MakeCode / MicroPython
• Optional: laptop to log base-station received messages

Inputs From Other Teams

• Comms: Provide a network plan (channels/groups, message rate).
• Data: Define packet schema + unique message IDs.
• Command & Control: Define reliability target (e.g., 95% delivered in 2 minutes).

What You Must Produce (Deliverables)

• A working 3-node demo: Payload → Relay → Base Station.
• A “packet format” including unique message IDs.
• A reliability test report (delivery rate + what you changed to improve it).

Step-by-Step Build

1. Define your packet schema:
   • MSGID (incrementing number)
   • SRC, REL, DST
   • DATA (e.g., temp/light)
2. Sender: transmit a packet every 1–3 seconds.
3. Relay: on receive, forward the packet to base station group/channel.
4. Base station: display/log packets and send an ACK back (by MSGID).
5. Relay and sender: retry sending packets not ACKed after a timeout.
6. Run reliability tests:
   • Close range baseline
   • Further range / obstructed test
   • “Busy air” test (two teams on nearby channels)
7. Optimise: adjust send interval, retry logic, or packet size.

Data Format / Output

Recommended text packet:

• MSG=42|SRC=S1|REL=R1|DST=GND|T=21|L=128
• ACK=42|FROM=GND

Analysis Ideas

• Delivery rate = ACKed / sent.
• Median time-to-ACK for packets.
• Compare delivery with and without retries.
• Identify failure causes: collisions, range, packet size, timing.

Success Criteria

• Base station receives and logs at least 50 packets.
• System demonstrates ACK + retry (not “fire and forget”).
• Team improves delivery rate through at least one design change and can explain why it helped.

Evidence Checklist

• Photo of 3-node setup (labels: Sender/Relay/Ground)
• Packet schema document
• Log/screenshot from base station (packets + ACKs)
• Reliability metrics + improvement note

Safety & Privacy

• No personal identifiers in packets.
• Avoid tripping hazards during range tests.
• Respect other teams’ radio channels; coordinate to reduce interference.

Common Failure Modes

• No unique message IDs → impossible to verify delivery.
• Retry storms (too many retries too quickly).
• Relay forwards to wrong channel.
• Packets too large → increased loss.

Stretch Goals

• Add hop count to prevent loops.
• Implement “store-and-forward” queue in relay.
• Build a simple dashboard: delivered %, avg latency.