Flight Software for the Double Asteroid Redirection Test

The NASA Double Asteroid Redirection Test (DART) mission, executed by the Johns Hopkins Applied Physics Laboratory (JHU/APL), is the first mission to successfully demonstrate the effectiveness of a kinetic impactor as a means of asteroid deflection. On September 26, 2022 at 23:14:24 UTC, the DART spacecraft collided with its intended asteroid Dimorphos, the smaller member of the (65803) Didymos binary asteroid system. The impact altered the orbital period of Dimorphos by 33 minutes, exceeding the minimum required alteration of 73 seconds.The DART Flight Software (FSW) was designed and developed to meet the needs of this unique mission. Most prominently, the DART FSW capabilities included (1) Guidance, Navigation, and Control (GNC) software for spacecraft attitude control, trajectory correction, solar array and communication antenna positioning, and autonomous optical targeting and guidance for asteroid impact, (2) the Digital Control Interface Unit (DCIU) software controller for NASA’s Evolutionary Xenon Thruster – Commercial (NEXT-C) gridded ion thruster system, and (3) software for configuring and monitoring on-board hardware systems, including the Didymos Reconnaissance and Asteroid Camera for OpNav (DRACO) optical instrument and associated hardware-based image processing and real-time image downlink data pipelines.The DART spacecraft impacted Dimorphos at a distance of approximately 11 million kilometers from Earth, requiring spacecraft operation with limited bandwidth and extended data transmission latency. The combination of several software capabilities addressed this need, including on-board data recorder management, reliable recorded data delivery, and a command system enabling real-time, time-tagged, and sequenced command execution. The communication bandwidth and latency constraints, in addition to deep space antenna resource availability, dictated the need for FSW to handle many on-board faults, including safing the spacecraft as necessary for manual diagnostics and recovery. This is done by an autonomous software-based fault protection system, referred to as Autonomy, with a flexible interpretive engine implemented in the DART FSW.Overall, DART development required a low-cost implementation in order to meet technical objectives within fiscal constraints. DART FSW addressed this objective by (1) leveraging numerous existing software components with flight heritage and (2) investing early in software development practices and tooling (DevOps) to complete FSW as-planned, minimizing late-breaking costs due to software defects or redesign efforts.This paper describes the overall DART Flight Software architecture, provides an overview of the avionics processing platform, details the specific FSW capabilities critical for mission success, explains the software development environment, discusses the approaches and results for both pre-launch testing and verification, and finally, provides results from post-launch operations and final successful asteroid impact.