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Flight Software

Flight software coordinates all onboard systems, from data handling and command execution to fault management and telemetry. This section explores software architectures, real-time operating systems, bootloaders, state machines, and common libraries used in CubeSat missions. Both bare-metal and RTOS-based approaches are included.

Software Architecture and Execution Model

To be added here:

  • Layered vs. monolithic architectures
  • Separation between hardware abstraction, services, and application logic
  • Event-driven vs. time-driven designs
  • Tradeoffs between simplicity and extensibility

Boot, Reset, and Update Strategy

To be added here:

  • Bootloaders and startup sequencing
  • Safe mode and minimal boot paths
  • In-flight software updates (when and when not)
  • Handling brownouts, resets, and partial failures

Command and Telemetry Handling

To be added here:

  • Command validation and execution models
  • Telemetry packet structures and rates
  • Housekeeping vs. payload data
  • Interaction with ground segment protocols

See also: Communications.

Inter-Subsystem Communication Protocols

To be added here:

  • Role of middleware in CubeSats
  • CSP vs. SpaceCAN concepts and tradeoffs
  • Addressing, routing, and fault isolation
  • Interaction with physical buses

Data Serialisation and Message Formats

To be added here:

  • Binary vs. structured formats
  • CCSDS packets and conventions
  • Lightweight formats (CBOR, protobuf, custom)
  • Forward compatibility and versioning

Modes, State Machines, and Autonomy

To be added here:

  • Mission modes and transitions
  • State machines vs. rule-based logic
  • Autonomy levels in CubeSats
  • Guard conditions and mode safety

Fault Detection, Isolation, and Recovery (FDIR)

To be added here:

  • Watchdogs and health monitoring
  • Threshold-based and rule-based fault detection
  • Recovery actions and escalation
  • Designing for partial failures

Timing, Scheduling, and Timekeeping

To be added here:

  • Task scheduling and priorities
  • Time sources (RTC, GNSS, ground sync)
  • Timestamping telemetry
  • Handling clock drift and resets

Software Testing and Validation

To be added here:

  • Unit and integration testing approaches
  • Flatsat and hardware-in-the-loop testing
  • Simulators and test harnesses
  • Regression testing before launch

See also: Assembly, Integration and Testing (AIT).

Flight Software and Hardware Interaction

To be added here:

  • Drivers and hardware abstraction layers
  • Power and inhibit awareness
  • ADCS and payload coupling
  • Thermal and EPS feedback loops

Documentation and Maintainability

To be added here:

  • Code documentation practices
  • Configuration vs. code
  • Knowledge transfer and bus factor
  • Preparing software for operations and handover

Resources

Open-source Flight Software Projects

  • NASA Core Flight System (cFS) – Modular, flight-proven framework used in many missions.
  • LibreCube Software – Open CubeSat components built around space communication standards.
  • OpenSatKit – Full dev environment based on cFS, with simulation and testing tools.
  • PyCubed – A fully open-source CubeSat avionics and software stack in Python/MicroPython.
  • OREsat – Modular open-source flight software stack developed by students at Portland State University.

RTOS and Embedded Platforms

  • FreeRTOS – Lightweight, widely used real-time OS for microcontrollers.
  • Zephyr Project – Scalable, secure RTOS with a growing presence in aerospace.
  • RIOT OS – Real-time OS for low-power, resource-constrained devices.

Commercial Platforms

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