1. The threshold between noise and message
Carl Sagan’s Contact returns as the recalled work because the characters in that novel spend enormous effort distinguishing a real signal from noise, then proving the distinction to others. A communications test has the same threshold: measured performance must exceed predicted margin by enough to be trusted, and the test must be repeatable enough to convince the team that the link will work on orbit.
This entry defines success and failure for the communications payload integration and link test.
2. Success criteria
The test is a success if the desktop can transmit and receive through its representative communications payloads under realistic conditions while respecting safety and policy constraints.
Specifically:
- Mechanical integration: antennas mount cleanly, boresights align within tolerance, and deployment mechanisms work.
- Electrical integration: radios power on within current limits, do not disturb the bus, and survive inrush and thermal conditions.
- RF link margin: measured received power matches the link budget prediction within an agreed tolerance, with margin at the worst-case low-elevation angle.
- Data rate: the link supports the required command, telemetry, and payload data rates at representative elevations.
- Link adaptation: the platform changes rate or coding in response to measured or predicted margin without losing lock.
- Data prioritization: high-priority data is delivered first; low-priority data is handled according to policy.
- Autonomous scheduling: the platform selects passes, resolves conflicts, and recovers from missed passes within policy.
- Security: authenticated commands are accepted; unauthorized commands are rejected.
- Coexistence: multiple radios can operate without harmful interference.
3. Failure categories
Failure is categorized by severity and response:
- Critical failure: the communications payload damages the bus, creates a safety hazard, or cannot establish any usable link. Response: redesign the subsystem or interface and retest.
- Major failure: the link closes but does not meet the required margin, data rate, or availability. Response: resize the link, change antennas or modems, or relax requirements, and retest.
- Minor failure: the link works but the scheduler response, prioritization, or logging is unclear or slow. Response: improve software and retest the affected scenario.
- Test artifact failure: the test setup, ground station simulator, or measurement is wrong. Response: fix the test and rerun before drawing conclusions.
4. What to measure
Objective measurements make success and failure defensible:
- transmit power and spectral purity;
- antenna gain and pattern, especially in the direction of the ground station;
- received signal strength versus elevation and range;
- bit error rate or frame error rate at each modulation and coding mode;
- link acquisition and reacquisition time;
- maximum sustained data rate;
- transmitter power consumption and thermal rise;
- scheduler decision time and pass selection accuracy;
- data latency and loss rate under priority and congestion tests.
5. What this changes
- Success means the desktop can communicate reliably and manage its communications autonomously.
- Failure is categorized by severity and response, not treated as a single stop signal.
- The next entry will close the communications test arc.