A Configurable Multi-Layer Protocol Framework for Spacecraft Command and Data Handling: Lessons from Firefly and a Path Forward

Spacecraft Command and Data Handling (C&DH) systems are fundamental to all missions yet typically require custom implementation for each satellite, resulting in 12-18 month development cycles and minimal code reuse. This paper presents lessons learned from developing the Pixxel Firefly constellation C&DH system and proposes a unified, configurable framework to address identified shortcomings.

The Firefly development experience revealed critical inefficiencies: repeated implementation of standard protocols, difficulty maintaining consistency across constellation nodes, and substantial integration testing burden. These challenges are common across the small satellite industry, where C&DH functionality is remarkably similar across missions despite custom implementations. Existing frameworks like NASA cFS and JPL F Prime, while comprehensive, are designed as complete spacecraft flight software systems with substantial resource footprints (>1 MB RAM, >2 MB Flash) that make them impractical for resource-constrained microcontrollers commonly used in small satellites.

We present a lightweight, focused five-layer modular framework (CSP, SDLP, SDLS, SPP, PUS) that extracts and implements only the command and data handling portion of spacecraft software, designed specifically for small MCUs. Unlike monolithic frameworks, our approach reduces development time by 80-85% through configuration-driven customization rather than custom coding. The framework supports selective layer deployment (272 KB to 400 KB memory footprint), maintains full CCSDS/ECSS standards compliance, and enables >80% code reuse across mission variants.

The framework addresses real operational challenges encountered in Firefly: configuration management across constellation nodes, security layer integration complexity, and ground system interoperability. By standardizing the common 90% of C&DH functionality while enabling mission-specific customization through declarative configuration, the framework offers a practical path toward reducing barriers to entry in the small satellite industry, particularly for resource-constrained platforms where existing heavyweight frameworks are not viable.