Flight software & fault recovery

Also known as FSW, FreeRTOS, Watchdog

State machines, real-time operating systems, brown-out bootloops, external watchdog hierarchies and non-volatile parameter storage on small satellites.

Document
SQ-SS-011
Updated
21 Oct 2026
Reading time
2 min
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Operating modes and the deployment timer#

Flight software (FSW) on a PocketQube or CubeSat is organized as a deterministic finite-state machine with four primary states[1]:

  1. Launch / Deployment wait: Entered on first power-up after leaving the deployer. RF transmitters and deployment heaters remain strictly disabled until a non-volatile elapsed-time counter reaches . If a brown-out resets the microcontroller during the wait, the counter resumes from non-volatile FRAM rather than restarting from zero[2].
  2. Detumbling & antenna release: Executes autonomous damping (if active is fitted) and fires primary and backup antenna burn resistors.
  3. Nominal / Sunlit & Eclipse: Samples housekeeping telemetry, transmits periodic beacons ( cadence) and schedules payload tasks when battery voltage exceeds the nominal threshold (e.g., ).
  4. Safe / Survival mode: Entered automatically when drops below a critical threshold (e.g., ). All payloads are shed and beacon duty cycle is reduced until solar charging restores energy margin.
Processor families in small-satellite on-board computers
FamilyCoreTypical role
MSP430FR16-bit, FRAMUltra-low-power 1P/1U OBC
STM32L4 / F4Arm Cortex-M4FGeneral-purpose OBC, ADCS
SAMV71Q21RTArm Cortex-M7Radiation-tolerant OBC
Zynq-7000Cortex-A9 + FPGAImage and payload processing

Representative parts, not an endorsement; radiation tolerance must be checked for each lot and mission.

References

  1. [1]NASA Small Spacecraft Systems Virtual Institute. (2026). Small Spacecraft Avionics. State-of-the-Art of Small Spacecraft Technology (2026 edition), Chapter 8. NASA Ames Research Center.nasa.gov(accessed 20 October 2026)
  2. [2]nadir lab. (2026). PocketQube picosatellites: A review of standards, mission trends and miniaturization constraints, with lessons learned from Grizu-263A, Türkiye’s first PocketQube [Preprint]. nadir lab.Read on nadir lab.
  3. [3]Bouwmeester, J. (2018). PQ9 and CS14 electrical and mechanical subsystem interface standard for PocketQubes and CubeSats, Version 1.0. DataverseNL.doi:10.34894/6MVBCZ

Cite this SatWiki entry

@misc{nadirlab2026flight,
  author       = {{nadir lab.}},
  title        = {{Flight software \& fault recovery}},
  year         = {2026},
  month        = oct,
  howpublished = {nadir lab. SatWiki SQ-SS-011 (Rev. 1)},
  url          = {https://nadirlab.space/en/wiki/flight-software/}
}