Simone Testino

Safety and Sensors

3 min read

ABSTRACT

Safety is paramount for an autonomous flying object. Luna features a robust, redundant safety architecture designed to detect anomalies and execute failsafe protocols instantly. This page details the sensor array, onboard logic, and emergency procedures.

Safety Philosophy

Luna is designed to be fail-safe.

  • Redundancy: Critical sensors are duplicated.
  • Autonomy: Safety logic runs onboard, not dependent on ground connection.
  • Passive Safety: In worst-case power loss, the system remains benign (balloon floats or slowly descends).

Sensor Architecture

The “Electronic Core” houses a comprehensive sensor suite monitored by dual Computation Centers (Arduino-based).

1. Environmental Sensors

  • Internal Temperature: Monitors Helium gas temp.
  • Internal Pressure: Barometric sensor to detect leaks or over-pressure.
  • Humidity: Monitors internal moisture levels.

2. Component Health

  • LED Thermometers: Direct PCB temperature monitoring.
  • Voltage/Current Sensors: Monitor power delivery and consumption.

3. Flight Dynamics

  • Inclinometers (Tilt): Measures lean angle (wind effect).
  • Accelerometers (IMU): Detects turbulence, impact, or sudden tether failure (free flight).
  • GPS (Optional): For geofencing in free-flight scenarios.

4. Gas Monitoring

  • Helium Concentration: Indirect measurement (via Oxygen sensors) to detect envelope rupture or air ingress.

The “Two-Tiered” Logic

As described in Software Architecture, the safety logic is simple and deterministic.

Tier 1: Warning (Yellow State)

Condition: Parameter exceeds normal range but is not critical.

  • Action:
    • Send telemetry alert to ground app.
    • Adjust active systems (e.g., 100% Fan Speed, Dim LEDs 20%).
  • Example: LED Temp reaches 85°C.

Tier 2: Critical (Red State)

Condition: Parameter reaches dangerous limit.

  • Action:
    • Cut Power to non-essential systems (LEDs).
    • Flash Emergency Signal (if LEDs operational).
    • Audible Alarm (Piezo buzzer).
  • Example: LED Temp > 105°C, or Pressure drops rapidly (leak).

Tier 3: Emergency Descent (Black State)

Condition: Catastrophic failure or “Ground Loss” (tether break).

  • Action:
    • Controlled Helium Release: Opens a small electronic valve to reduce lift.
    • Goal: Slow, safe descent (< 2 m/s) to the ground.
    • Strobe Lights: Visual warning to bystanders.

Sensor Discrepancy Protocol

With dual sensors, what happens if they disagree?

  • Small Deviation: Average the two values. Log a “Sensor Drift” warning.
  • Large Deviation:
    • Assume the Worst Case value is true (Fail-Safe).
    • Example: If Temp A = 40°C and Temp B = 90°C, system acts as if Temp is 90°C.
    • Trigger “Sensor Failure” alert.

Communication Redundancy

Safety alerts are transmitted via two independent channels:

  1. Wired (Primary): Data over Power (PLC) or dedicated twisted pair in the tether.
  2. Wireless (Secondary): LoRa or Wi-Fi link to ground station/phone.

If the wired link is cut (tether failure), the wireless link takes over to trigger emergency protocols or receive manual “Land Now” commands.

Physical Safety Features

  • Non-Flammable: Helium is inert. Materials are self-extinguishing where possible.
  • Low Voltage Control: User interface is low voltage; high voltage is contained.
  • Soft Impact: The balloon is lightweight and flexible; impact risk to people/property is minimal compared to falling metal towers.

This comprehensive approach ensures Luna meets or exceeds safety standards for construction and event equipment.

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