Software Architecture

ABSTRACT

Luna’s software is divided into two distinct domains: a high-fidelity Physical Simulation Environment (Python) for design validation, and a lightweight, real-time Onboard Safety System (C++) for operational control. This page details both architectures.

1. Ground-Based Physical Simulation (Python)

Before any physical prototype is built, Luna is “flown” in a digital twin environment. This approach saves time and money by validating physics and optimizing parameters virtually.

Architecture

• Language: Python 3.x
• Libraries: NumPy (math), SciPy (solvers), Matplotlib (visualization).
• Structure: Object-Oriented Design. A Luna class integrates sub-models.

Core Models

1. External Fluid Dynamics:

   • Calculates Drag ($F_D$) and Lift ($F_L$) vectors.
   • Solves for equilibrium angle $\theta$ under wind load $v$.
   • Output: Tether tension requirements, max wind rating.

2. Internal Fluid Dynamics & Thermodynamics:

   • Models helium flow driven by fans.
   • Solves heat transfer equations: $Q_{LED}\to Helium\to Envelope\to Air$.
   • Output: Equilibrium temperatures for LEDs and Gas.

3. Optical Model:

   • Simulates light projection from height $h$.
   • Calculates ground illuminance $E(x,y)$.
   • Output: Optimal height and LED power for target lux.

4. Permeation Model:

   • Uses Arrhenius equation for gas diffusion.
   • Output: Refill interval predictions.

TIP

The code for these models is available in the GitHub Repository and documented in the Physical Models section.

2. Onboard Safety System (Embedded C++)

The flight software runs on the internal microcontroller (Arduino). It is designed for determinism, speed, and fail-safety.

Architecture

• Platform: Arduino (C++).
• Loop Cycle: < 100ms (Real-time monitoring).
• State Machine: The system operates in defined states (Idle, Flight, Warning, Emergency).

Core Modules

A. Sensor Fusion Engine

• Reads raw data from redundant sensors (Temp A/B, Pressure A/B).
• Applies calibration and filtering.
• Discrepancy Check: If $|A-B|>Threshold$, flag error and use worst-case value.

B. Safety Logic Controller

• Compares fused sensor data against Critical Parameters (derived from Python simulations).
• Rules Engine:
  • IF Temp > T_WARN THEN Fan_Speed = 100%
  • IF Tilt > MAX_TILT THEN Trigger_Alert()
  • IF Pressure < MIN_P THEN Trigger_Emergency_Land()

C. Communication Manager

• Telemetry: Streams status (Temp, Batt, Tilt) to ground @ 1Hz.
• Command: Listens for ground commands (“Land”, “Dim Lights”).
• Heartbeat: Sends “I’m Alive” signal. If ground loses heartbeat, it alerts operator.

D. Actuator Control

• LED Driver: PWM control for dimming.
• Fan Driver: PWM control for speed.
• Valve Control: Solenoid activation for helium release (Emergency).

3. Mobile App (User Interface)

A companion app for ground operators.

• Connection: Bluetooth LE (BLE) or WiFi.
• Features:
  • Real-time dashboard (Temp, Wind, Battery).
  • Control panel (Brightness, Height - if winch equipped).
  • “Black Box”: Logs flight data for post-flight analysis.
  • Setup Wizard: Step-by-step guide for safe deployment.

Development Workflow

1. Simulate: Run Python model to find safe limits (e.g., “Max Temp = 85°C”).
2. Code: Hardcode these limits into the Arduino firmware.
3. Test: Verify logic with hardware-in-the-loop (HIL) testing.
4. Fly: Deploy code to Luna.

This rigorous separation of “Design Logic” (Python) and “Control Logic” (C++) ensures that the onboard system remains lightweight and bug-free.