Adamant: A Soon-to-be Open Source, Mission-Critical Flight Software Framework Written in Ada

The challenge faced by flight software engineers at the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder became evident when tasked with developing the onboard software for NASA's new Climate Absolute Radiance and Refractivity Observatory (CLARREO) Pathfinder Reflected Solar mission. The goal of measuring Earth-reflected sunlight with an accuracy of 0.3 percent (k=1), surpassing existing sensors by five to tenfold, from an instrument mounted beneath the International Space Station (ISS), produced a complex set of requirements.

The avionics needed to balance multiple functions, including a high-rate control law, numerous hard real-time deadlines, interfaces with half a dozen external subsystems, and management of commands, telemetry and fault protection, all while capturing high-resolution science images at 15 frames per second. Ensuring uninterrupted operation within the unforgiving environment of low-Earth orbit necessitated the software run on a single Arm Cortex-M1 microprocessor instantiated at 50 megahertz (MHz) inside a radiation tolerant field-programmable gate array (FPGA) (Microchip RTG4), with only 4MB of RAM. The engineers quickly realized that existing flight software solutions at LASP were not equipped to handle this combination of hard real-time performance and heavy multitasking within such a constrained processing environment.